Aligning Table Saw Sled Fence - Five Cut Method

[Jon Rista]

I recently built a new table saw sled. My first was pretty pitiful, and I wanted to make a more versatile sled that could accommodate my miter gauge as well as a number of clamps if necessary. Also wanted a micro-adjustable stop, and a way to easily make adjustments down to a 32nd. I finished the sled a little while back, and then moved on to making other jigs and sleds. Today, I've been working on aligning the fence. I'm using the 5-cut method, which I learned about from this video (which seems to be the original, its apparently 13 years old! I've heard about it on other sled videos but thought this one was far more in depth as to how the method worked.)

A = T-B/4/L*R

A - Adjusment to make to fence (positive, move corner opposite of pivot out, negative move in)
T - Top of fifth cut, thousandths
B - Bottom of fifth cut, thousandths
L - Length of fifth cut, inches (could also be thousandths)
R - Radius of fence from pivot, inches (could also be thousandths, units have to agree with L)

I am pretty sure I am running the calculations correctly. I make the four cuts, just barely trimming along the full length of the four initial edges, then on the fifth cut I cut off about a 1" wide strip. Mark the top, measure top and bottom, run the calculation exactly as described in the video (for reference I wrote it down above), and initially I was off by -0.021 or about 21 thousandths. So I made the necessary adjustment, shifted the corner opposite my pivot into the sled by that amount (using my feeler gauges, exactly as described in the video), and I was pretty confident that the adjustment was correct. The feeler gauge slipped into the gap between the pointed "stop" block and the fence nicely, without friction but without any gap or looseness. However, after making the adjustment, clamping the fence in place, drilling a hole, and driving the screw in....

My next set of 5 cuts resulted in a much worse error of +0.089! I was very careful and meticulous in my process, so I was surprised at such a discrepancy. I decided to check with a square, and according to the square, things did not look that far off, and in fact the error still appeared to be "negative"... Well, I was quite confused by that, and decide to dry another larger construction square. That one showed the opposite, a slight positive error (so now, I suspect that some of my squares, may not in fact actually be truly square...I bought a set of three, small/medium/large, and I am now suspicious that all three might have accuracy issues....and, IIRC they were made in...yup, china.) I checked my larger square against a couple of construction quick squares, which I know are pretty accurate, as well as my largest engineering square (which is still rather small compared to the construction square), and they all seem to agree as far as I can tell.

Ok, so, I'm now off positive 89 thousandths. I redo the math, and double, triple check everything, make sure I'm not too loose or too tight on the feeler. Make the adjustment.

My next five cuts, are now -0.105!!!! Checking with my construction square, seems to agree.

So I did it one more time. Now its +0.0305. It seems the swing, gets worse every time, but I cannot actually account for exactly why...although, I have one suspicion (more in a moment.)

I'm a bit baffled here. I've rewatched the parts of the video with the math about a dozen times now. There are a couple points where he covers the concept and the math, and its around 29 minutes where he actually runs the process on his newly created sled, and I am pretty sure I'm running the math correctly. Also pretty sure my numbers are correct. The length of my fence from the pivot point is 22.85", while the while fence length is a little shy of 24". There is about 3/4" or so offset from the pivot end of the fence where my screw that I'm pivoting around actually is. So the number there seems correct (not that it matters that much, a tenth of an inch up or down and it doesn't affect the final result enough to matter, as its in the 1-thou or less range.) I've checked my feeler gauges against my calipers in thousandths, and they agree. The last time I made the fifth cut, I measured about five times each. I zeroed the calipers after each measurement after making sure I'd fully, fully closed them. So I am pretty sure my measurements are within a thousandth. The numbers from my last run are:

R = 22.85
L = 17.3125

T = 0.540 (measure at top of cut 5 strip)
B = 0.446 (measure at bottom of cut 5 strip)

D = 0.094 (subtract; T-B)
C = 0.0235 (divide; D/4)

E = 0.00136 (divide by L; this is my actual error)

A = 0.0305 (multiply by R; this is the error transformed from the cut 5 test strip to the fence)

So I'm now in need of another positive adjustment, by 30 thousandths. I'm afraid to drill another hole in my fence, here, until I know for sure what's going on. Unless someone can show me an error in the math here, the only other thing I can think of, is the drilling process, or the process of screwing in the screw into the new hole, is somehow causing a shift? I tried to drill a countersink into the first couple of holes, but, with this wood and my bit, I'm not getting a perfectly round countersink, its more polygonal. I am wondering if that might be causing problems, but, I also tried to just screw it in without a countersink, letting the impact driver sink it for me. I had errors in either case.... Is that the problem? Is screwing in the screw, or maybe drilling the hole, or something, causing a shift in the fence? Outside of that, I honestly am not sure what else could be causing the problem... Based on the discrepancy in the T vs. B values of the last 5th cut, its clearly not good enough, and will result in not totally square cuts. I think I read or heard in a video, that 5 thousandths or less is good enough, but I'm 6x that.

Anyway...if anyone has any insights, I'm all ears. This is the last thing I need to do, to get my new sled into operation. Maybe I'd just nail it after making a 30 thousandths adjustment here...but, after three failures, I don't want to drill any more holes until I know for sure my math is right, and if it IS the darn screws....hopefully someone will have a tip to avoid shift. FWIW, I AM clamping the fence in place after making the adjustment and before drilling the hole...but, there can always be tension added by screwing in a screw, and maybe that is causing a shift that occurs after I release the pressure from the clamp?

Thanks for any help.

 

[Mike Selser]

A couple of questions. Are you making the cuts in the proper sequence, i.e is the side against the fence the side that was cut on the previous cut? Is the 22.85” the distance from the pivot to where you are making the adjustment with the feeler gauge? If that is the case then drilling the new hole and setting the screw is probably causing the fence to shift. The way it is usually done is to have a fixed pivot point and an adjustable point that is a bolt in an oversized hole that can lock the fence securely in place. After a couple of iterations you are usually close enough to drill a hole that locks the fence in place permanently. If the bolt in the oversized hole is locking the fence securely then I don’t see how drilling a new hole and putting a screw in it can be shifting the fence. If you are just drilling a new hole without the fence securely locked in place then that is definitely a problem.

 

[Kevin Jenness]

I've used the 5 cut method and found it too fiddly. I went back to using a 3 cut method, simpler and equally accurate.

1. Straigten the long edge of a workpiece as wide as your sled will cut and at least twice as long.
2. Make a crosscut in the middle of the piece.
3.Flip one of the halves over end for end, so that it is upside down with the same reference edge against the fence and crosscut it again.
4. Flip it back over and butt the the crosscut ends together in their original orientation, with their reference edges against the fence. Any gap is twice the divergence from square. Assuming the fence is truly straight and your runners are a good fit in the slots you should be able to dial it in to +/- .005" over 24".

Mike's post is right on. Adjust the fence until you get an acceptable result, lock it in that orientation and pin it permanently.

 

[Brian Gustin]

What Mike touched on: Math is applicable only on the PIVOT POINTS and MEASURING POINTS of the fence - you'll want to measure your fence length from the pivot point for your calculations, not the total length - Myself, I would make an even number measurement to make the math easier (and mark it all out on the fence) , and second, I had the same issue with figuring which way to shift fence and how much, and like Mike said, it is very important to be doing your feeler gauge measurements at the same place as you marked your fence length (I.E. your measured fence length, not your actual fence length)

And lastly as he said, you want to be sure your fence , once adjusted, does not move - As he suggested, a slotted hole for your fastener screw (which should be a flat head screw, drill a countersink recess with forstner bit - a typical wood screw is going to make fence shift when you tighten it down.) and even nicer, you can build a temporary micro adjuster with a block of wood (CA glued in place) and a fine threaded screw (such as M5 -0.8) to make it easier to just snug the fastener screw and then micro-adjust fence to where it needs to be...

 

[robo hippy]

I have yet to make another cross cut sled. I have no clue as to why no one has thought of this yet.... I would make a back stop for the sled that extended off of the end of the table saw, after first making sure the back stop is plumb and straight, with all sides being square. Put a big square on your blade to mark an approximate "square" orientation. Make a cut with about a 12 inch wide piece of plywood, and then put a true square on the end to see how close the cut is. Adjust the back stop as needed and check it a couple of times. Next, dribble some CA glue along both sides to anchor it in place. Allow glue to set, then flip it over and add screws. No math required....

robo hippy

 

[Jon Rista]

A couple of questions. Are you making the cuts in the proper sequence, i.e is the side against the fence the side that was cut on the previous cut? Is the 22.85” the distance from the pivot to where you are making the adjustment with the feeler gauge? If that is the case then drilling the new hole and setting the screw is probably causing the fence to shift. The way it is usually done is to have a fixed pivot point and an adjustable point that is a bolt in an oversized hole that can lock the fence securely in place. After a couple of iterations you are usually close enough to drill a hole that locks the fence in place permanently. If the bolt in the oversized hole is locking the fence securely then I don’t see how drilling a new hole and putting a screw in it can be shifting the fence. If you are just drilling a new hole without the fence securely locked in place then that is definitely a problem.

Yes, I am indeed making the cuts in the proper order. Side one first, then a CLOCKWISE rotation, to put that cut edge along the fence, to make cut two, etc. etc.

Also, yes, the distance of 22.85" is from the pivot point to the point of contact where the feeler gauge is. I actually drew a line a little in from the end of the fence, and have been repeatedly using that same point for all feeler gauge measurements.

So I am guessing its the drilling and screwing. I am not sure how to accommodate a bolt. I put an Incra t-track rail with a ruler in it on the top... I AM, however, clamping the fence in place, before I drill the hole or screw it in place. That's generally the recommendation of most from videos I've watched, but....maybe I'm using a poor quality screw, or my drill bit is too small? I am NOT, however, drilling without the fence being securely held in place by a clamp...so its not freely swinging, nor am I just trying to hold it in place with only my hand or something like that. I wonder, if maybe I need to use a few clamps, maybe closer to where I'm drilling and screwing...

What Mike touched on: Math is applicable only on the PIVOT POINTS and MEASURING POINTS of the fence - you'll want to measure your fence length from the pivot point for your calculations, not the total length - Myself, I would make an even number measurement to make the math easier (and mark it all out on the fence) , and second, I had the same issue with figuring which way to shift fence and how much, and like Mike said, it is very important to be doing your feeler gauge measurements at the same place as you marked your fence length (I.E. your measured fence length, not your actual fence length)

And lastly as he said, you want to be sure your fence , once adjusted, does not move - As he suggested, a slotted hole for your fastener screw (which should be a flat head screw, drill a countersink recess with forstner bit - a typical wood screw is going to make fence shift when you tighten it down.) and even nicer, you can build a temporary micro adjuster with a block of wood (CA glued in place) and a fine threaded screw (such as M5 -0.8) to make it easier to just snug the fastener screw and then micro-adjust fence to where it needs to be...

Aye. Sorry, I should have been clearer. I did mark a line, where I measure the feeler guage, and the measurement is from the pivot point (which I also marked with a line) to that mark. Its not actually to the very end of the fence. The mark is a little in from the end of the fence. I wanted to make sure I could place the "pointer" piece of wood, against a guaranteed flat face. The wood I used for this sled....it was sold as "baltic birch", however, I am not sure if it really is? It seems to actually be veneered plywood, with a VERY THIN veneer of nice wood, over, that I think, are cheaper plies underneath. The darn thing, 2x4 foot, cost me $48, and I'm pretty dismayed with it, as the veneered surface splinters, even when you tape across your cuts and all. It splinters a bit on the incut side, and badly on the outcut side. So, wherever I had a cut, that darn veneer is messed up, despite me taping over where every cut was going to be. So I put a mark in far enough that I'm free of the splitered veneer, and I DID measure from pivot to that point. I accidentally started with about a 23.5" measurement, to the very end of the fence, before I corrected it. The differnece in teh final results, was 1 thousandth or less, so I don't think the small discrepancy would matter much, but, I am indeed measuring to the point where I measure the feeler.

So, regarding the second part here...I think you are saying use something like this:

In the bottom of the swing-end of the fence. Then with a forstner drill a hole a bit larger than the screw that would thread into this, so I have some room to adjust, lock the screw down and rinse/repeat until its dialed in? I think I can do that, since unlike a bolt with a nut, I wouldn't have to worry about the T-track I put on top of the fence. I may have some screws and T-nuts floating around that will work.

 

[Terry Brown]

I have yet to make another cross cut sled. I have no clue as to why no one has thought of this yet.... I would make a back stop for the sled that extended off of the end of the table saw, after first making sure the back stop is plumb and straight, with all sides being square. Put a big square on your blade to mark an approximate "square" orientation. Make a cut with about a 12 inch wide piece of plywood, and then put a true square on the end to see how close the cut is. Adjust the back stop as needed and check it a couple of times. Next, dribble some CA glue along both sides to anchor it in place. Allow glue to set, then flip it over and add screws. No math required....

robo hippy

A few things to add to Robo's good, simple directions.
First you MUST make sure that your square is true/square.
Second when making a saw cut for calibrating, remove approximately 50% more wood than the saw kerf width.
Third secure the plywood to the sled with screws, then cut it.
Now use the plywood and SQUARE to adjust the fence and secure it as he described.

 

[Jon Rista]

A few things to add to Robo's good, simple directions.
First you MUST make sure that your square is true/square.
Second when making a saw cut for calibrating, remove approximately 50% more wood than the saw kerf width.
Third secure the plywood to the sled with screws, then cut it.
Now use the plywood and SQUARE to adjust the fence and secure it as he described.

So, point three....I am not sure I really understand that one. I am also not sure I understand using the square and plywood. I assume by plywood here, you mean the piece of wood I am using to perform the calibration? My sled is also made of plywood, so, just making sure.

I am pretty sure my construction square is truly square. However, I am not real sure how to actually check that with any true guarantee. I've checked it against other squares...

Thus far, I think I've been taking a kerf OR MORE off the calibration piece of wood? What I was doing, is aligning the short end, such that that end lined up with the other side of the kerf in my sled (well, a bit more, I guess). So when I cut, at a minimum it was a bit over a kerf, then additional to whatever the wider side was.

 

[Jon Rista]

I have yet to make another cross cut sled. I have no clue as to why no one has thought of this yet.... I would make a back stop for the sled that extended off of the end of the table saw, after first making sure the back stop is plumb and straight, with all sides being square. Put a big square on your blade to mark an approximate "square" orientation. Make a cut with about a 12 inch wide piece of plywood, and then put a true square on the end to see how close the cut is. Adjust the back stop as needed and check it a couple of times. Next, dribble some CA glue along both sides to anchor it in place. Allow glue to set, then flip it over and add screws. No math required....

robo hippy

Ok. So, this is actually what I started with. It was a...few weeks ago I guess, right after I'd finished the initial build. I used my squared to align the fence. I wasn't sure if it would be good enough, but I switched to making some of the other sleds and jigs. I got back to this main crosscut sled the other day, and decided to try and dial it in as best I could. I'd heard of the 5-cut method, and decided to give it a try. Where I started out in my first post, at 21 thousandths off...would have been what I ended up with using my squares to align the fence originally. So, I don't know, I guess it wasn't necessarily "bad" originally? Even at 21 thousandths though (and that's along the length of my fence, which is just about two feet, 24"), I could actually see that by the fifth cut, there was a slightly visible discrepancy between the top and bottom of that first "5th cut" that I measured. From what I've read and heard in YT videos, 5 thousandths or less, is what you want, as by the time you get down to 5 thousandths the discrepancies if you make multiple cuts, won't compound enough to matter for the majority of woodworking.

So that's been my goal...and, since I ultimately want to get into segmented turning (watching people do segmented vases and bowls, was what actually attracted me to woodworking in the first place...that was 2018, maybe the end of 2017, when I started watching woodworking videos, and I just love segmented pieces, particularly vases.) So the goal is to make sure I can make those kinds of segment cuts accurately enough, to avoid any issues when the segments are assembled into rings, and the rings stacked to make something turnable.


So, from that original 21 thou error...I honestly don't think I could have made the adjustment for that myself, by hand... The feeler gauge technique from the video (which, I do apologize...I just realized the link never made it into my original post) was actually quite genius, and the way that worked, it made it easy to make exactly the right adjustment (which, I think, I was successful at...up until the point of screwing the fence/backstop in again.) I don't feel like its good enough? My construction square, FWIW, is pretty long...the long edge doesn't actually fit between my sled's front and back fences. I've used the shorter end, which is still most of the distance between the two fences, aligned along the blade (which I fully extended), with the longer edge up against the front fence. I actually checked that again just before I came in from the shop and started writing this post...and, I could actually tell that there was a slight error, which currently is the 30.5 thousandths, or basically three hundredths. The swing end of my fence is indeed still slightly forward, and that proves out with the square (there is a gap at the corner, near the zero-clearance slot in my sled, that I can just about fit a .030 feeler into.

View: https://www.youtube.com/watch?v=UbG-n--LFgQ


This video is the one, and it may be "the original" for the 5-cut method? I've heard of it many times, and watched numerous videos on it, but no one really went into the exact nature of it like this guy, and he didn't seem to reference anyone else, seemed like he was teaching it OG. He goes through it at the beginning, then actually builds a sled, and near the end (20 minutes or so in), he actually applies the technique to the fence for that sled, and shows exactly how he uses that pointed piece of wood and a feeler to basically make exactly the right adjustment.

I am also starting to wonder, if my issue may be in part due to the quality of plywood. I bought this darn 2x4' sheet for nearly fifty bucks, but, it actually seems to be pretty cheap and crappy stuff. The paper-thin veneer on it, just splinters out with every cut, and nothing I've done seems to prevent that. So it can't take a cut. The internal plys seem rather....well, not great, maybe even a little punky? I bought it a while ago, actually bought two of them. I've used up most of it now, making a few different sleds and some jigs (and also for the front and back fences of each, etc.) for my table saw, bandsaw and drill press. I don't have much left, maybe a 1.5x1.75' piece? So I probably don't even have enough, to make the really long backstop you mentioned. I guess if the fence was indeed long enough...that might make it possible to make the necessary adjustment, since the magnitude of the angle at the end of, what, four feet/48" (?) would be bigger than at 22-23".

Well...right now, I am off by three hundredths, 0.0305". The error is not huge, and...I may try this larger hole in the base for adjustment with a metal thread embedded in the end of the fence, and see if I can dial it in with that. If I can't get that to work, I'll revisit.

 

[Jon Rista]

And lastly as he said, you want to be sure your fence , once adjusted, does not move - As he suggested, a slotted hole for your fastener screw (which should be a flat head screw, drill a countersink recess with forstner bit - a typical wood screw is going to make fence shift when you tighten it down.) and even nicer, you can build a temporary micro adjuster with a block of wood (CA glued in place) and a fine threaded screw (such as M5 -0.8) to make it easier to just snug the fastener screw and then micro-adjust fence to where it needs to be...

Ok, started looking into doing this with a T-nut, and decided that wouldn't work. The T-nut just kind of presses into the wood, and when you are threading in something from the OTHER SIDE of said wood, they work since the flange gets pulled into the wood. For this use case, if I synched a screw from below the sled down, it would probably just pull a T-nut out.

I'm curious what other option there is. You said "fastener screw", and when I search for that, I just find "screws"...is there a proper name for what you are talking about? I think I know what it is, but I can't think of the proper name for them right now, and I can't find them. It may be that Ace has the thing I think you mean, and a new one just opened up down the road a month or so ago. But I just can't remember the name...even though I can picture it in my head. Do you know what they are called? Or maybe it is "Fastener screw", sadly, when I search for that, I get pages just for screws. All the kind sof screws (or fasteners) you could imagine.

 

[Brian Gustin]

Ok, started looking into doing this with a T-nut, and decided that wouldn't work. The T-nut just kind of presses into the wood, and when you are threading in something from the OTHER SIDE of said wood, they work since the flange gets pulled into the wood. For this use case, if I synched a screw from below the sled down, it would probably just pull a T-nut out.

I'm curious what other option there is. You said "fastener screw", and when I search for that, I just find "screws"...is there a proper name for what you are talking about? I think I know what it is, but I can't think of the proper name for them right now, and I can't find them. It may be that Ace has the thing I think you mean, and a new one just opened up down the road a month or so ago. But I just can't remember the name...even though I can picture it in my head. Do you know what they are called? Or maybe it is "Fastener screw", sadly, when I search for that, I get pages just for screws. All the kind sof screws (or fasteners) you could imagine.

OK lemme organize my thoughts here...

1) I should have said more like a pocket hole screw (the kind with formed washer on the head) it'll have a flat surface that will let it slide within the hole (counterbored) if you drill the hole through a bit larger than the screw size , then the little pilot hole in the fence , you'll be able to snug it such that the fence won't move unless you can "nudge" it one way or another (which led me to suggest the micro adjuster block fastened to back of sled to push the fence in tiny increments and keep it from shifting back when you tighten down the pocket hole screw , although that'd be kind of overkill really as opposed to just lightly snugged pocket hole screw you can tap fence in or out as needed)

2) Another thing to be sure of is your sled runner - if your sled shifts in the miter track slot of the table saw you'll never get it square (and, even with the adjustable sled runners, it's still good practice to push the sled to one side or the other every cut, just to take up all the slack.)

3) Of course, obviously your saw blade needs to be perfectly square to the miter slot as well (Basic table saw adjustment - the more perfect you can get it the more square your cuts will be)

4) I ended up not bothering with my first 2 versions of sled because of my cheapo skil table saw, and instead made a sled that I can adjust the fence (up to a 60 degree cut) by routing the bolt hole slot with palm router on trammel (and a recess slot for a carriage bolt) and a locking knob on top of fence - that way I can (and often have to) re-square my fence every time I use the sled, it only takes a few seconds (I do 2 cuts - First I cut a piece of scrap to have perfectly parallel sides so either side can be a reference edge, then I will make a cut and flip the board over and cut about half an inch off , then measure the difference between top and bottom - Usually I'm within .0005 or less using my machinist's micrometer when I have it squared on a 6 inch wide board. for more precision than that, I use a shooting board and No 5 1/2 hand plane)

 

[Kevin Jenness]

I am pretty sure my construction square is truly square. However, I am not real sure how to actually check that with any true guarantee. I've checked it against other squares...

To check a framing square against itself, first get a woodlike panel with a straight edge, at least as wide as the tongue of the square and twice as long as the blade.. Register the square's blade against the reference edge and strike a line along the tongue.with a sharp knife near the panel's center. Flip the square over and compare the tongue with the scribed line. Any difference represents twice the square's inaccuracy relative to "square". To correct the problem, peen the inside or outside corner of the square using a center punch and hammer to expand the metal and change the angle.

Accuracy in woodworking is simple in concept and devilish in the details. Deciding what is "close enough" takes some experience and judgment. Take the starting point of the procedure described above, a panel with a straight edge. What is straight? How would you know if the panel has a straight edge? I happen to have a Starret 6" metal straightedge certified to within .001" but it ain't cheap and I only pull it out for machine setups. I also own a sliding tablesaw with an 8' stroke designed for cutting sheet goods which will cut a straight line within a few thousandths. I know this because I can cut two long panels, place them edge to edge, and they match up with no gaps. Not too many hobbyists have those resources, so you may have to use a similar approach as testing the square against itself. Take your "straight-edged" panel, lay it on another, strike a line against the reference edge, flip it over and compare the edge and the scribed line. Correct it using a long hand plane or sanding block and check again. Once you have a true straight edge you can check your square, but without that you are floundering. (I hate to complicate things, but it's worth checking the edges of your so-called square for straightness and parallelism- mass market framing squares are basically sheared and deburred, not machined.)

If you are interested in precision and accuracy it's worth investing in a good metal straightedge as long and accurate as you can afford, a digital or dial caliper, a dial indicator and a machinist's square. You can do a lot, though, with common sense and simple procedures as described above.

 

[Jon Rista]

OK lemme organize my thoughts here...

1) I should have said more like a pocket hole screw (the kind with formed washer on the head) it'll have a flat surface that will let it slide within the hole (counterbored) if you drill the hole through a bit larger than the screw size , then the little pilot hole in the fence , you'll be able to snug it such that the fence won't move unless you can "nudge" it one way or another (which led me to suggest the micro adjuster block fastened to back of sled to push the fence in tiny increments and keep it from shifting back when you tighten down the pocket hole screw , although that'd be kind of overkill really as opposed to just lightly snugged pocket hole screw you can tap fence in or out as needed)

2) Another thing to be sure of is your sled runner - if your sled shifts in the miter track slot of the table saw you'll never get it square (and, even with the adjustable sled runners, it's still good practice to push the sled to one side or the other every cut, just to take up all the slack.)

3) Of course, obviously your saw blade needs to be perfectly square to the miter slot as well (Basic table saw adjustment - the more perfect you can get it the more square your cuts will be)

4) I ended up not bothering with my first 2 versions of sled because of my cheapo skil table saw, and instead made a sled that I can adjust the fence (up to a 60 degree cut) by routing the bolt hole slot with palm router on trammel (and a recess slot for a carriage bolt) and a locking knob on top of fence - that way I can (and often have to) re-square my fence every time I use the sled, it only takes a few seconds (I do 2 cuts - First I cut a piece of scrap to have perfectly parallel sides so either side can be a reference edge, then I will make a cut and flip the board over and cut about half an inch off , then measure the difference between top and bottom - Usually I'm within .0005 or less using my machinist's micrometer when I have it squared on a 6 inch wide board. for more precision than that, I use a shooting board and No 5 1/2 hand plane)

Thanks.

I used some HDPE runners that were explicitly sized for miter track. There is no play at all. In fact, I accidentally got a little bit of CA glue on the side of one of the miters, and it currently takes too much force to slide. Once I get some more Acetone and clean that up, the runners should be PERFECT fit. They won't change size with humidity, and there is no play at all, but they do slide well. So that should be covered.

As for alignment of the blade, that's done. Actually, it was the very first thing I did after first setting up the saw. I aligned both the fence, as well as the blade, and the blade is aligned relative to the miter slots as well as the fence. So everything is aligned together. I did check that before I started building this sled, and everything was till perfect as far as I could tell. When I first got the saw, the tail of the blade was a little out of alignment, and the fence was actually well out of alignment (nearly an 8th of an inch!) I did cut the slot in the sled itself, and it does seem to be perfectly strait, all the way through, and it maintains its thickness along its length. I'm pretty sure the sled itself (the plywood base) and the runners and the blade, are as good....well, as I can get them, with the equipment I have. I was pretty meticulous with the measurements, used exactly the same tooth on the saw for front and back measures, all that. I don't have one of those dial indicator devices to measure down to thousandths, but I think it is pretty darn good overall. Even if I could measure down to thousandths, its a Ridgid job site saw, and does not have anything nice like adjustment set screws or anything like that...I doubt I could really dial it in much better than it is anyway, as it has to be done entirely manually by hand.

I think I finally remembered the name of that nut: Insert Nut. I was trying to think of something that I know would actually HOLD into the bottom wood of the fence, allowing me to synch the screw down, at least a bit. I think something like this would do:

Amazon.in

I actually have a few in 1/4x20, so I'm going to give one a try and see how it goes. I've used these for a few things in the past, and with the right pilot hole they hold real tight, so it should work.

The one thing I am wondering about now...is exactly how to drill into the bottom of the sled. At first I was thinking all the way through, but, I have to countersink the screw down there...so now I am actually not entirely sure what to do. Especially since I'll probably have to drill it by hand. The plywood is 3/4" thick, maybe I can drill partially through with a forstner, enough for a different kind of screw and maybe a washer to fit, and still not protrude below the base of the sled...

 

[Jon Rista]

To check a framing square against itself, first get a woodlike panel with a straight edge, at least as wide as the tongue of the square and twice as long as the blade.. Register the square's blade against the reference edge and strike a line along the tongue.with a sharp knife near the panel's center. Flip the square over and compare the tongue with the scribed line. Any difference represents twice the square's inaccuracy relative to "square". To correct the problem, peen the inside or outside corner of the square using a center punch and hammer to expand the metal and change the angle.

Accuracy in woodworking is simple in concept and devilish in the details. Deciding what is "close enough" takes some experience and judgment. Take the starting point of the procedure described above, a panel with a straight edge. What is straight? How would you know if the panel has a straight edge? I happen to have a Starret 6" metal straightedge certified to within .001" but it ain't cheap and I only pull it out for machine setups. I also own a sliding tablesaw with an 8' stroke designed for cutting sheet goods which will cut a straight line within a few thousandths. I know this because I can cut two long panels, place them edge to edge, and they match up with no gaps. Not too many hobbyists have those resources, so you may have to use a similar approach as testing the square against itself. Take your "straight-edged" panel, lay it on another, strike a line against the reference edge, flip it over and compare the edge and the scribed line. Correct it using a long hand plane or sanding block and check again. Once you have a true straight edge you can check your square, but without that you are floundering. (I hate to complicate things, but it's worth checking the edges of your so-called square for straightness and parallelism- mass market framing squares are basically sheared and deburred, not machined.)

If you are interested in precision and accuracy it's worth investing in a good metal straightedge as long and accurate as you can afford, a digital or dial caliper, a dial indicator and a machinist's square. You can do a lot, though, with common sense and simple procedures as described above.

Thanks for the info.

I don't know if I have the necessary tools to try and fix my square. I will try to measure it and see if its truly square or not. Based on the fact that it seems to agree pretty closely with the 5-cut method so far, I think, at least, its pretty close. Maybe within 10 thou?

Regarding what is strait... That is a good point. Another video I watched was from my favorite jig and sled girl, where she clamped a level to the two pieces of her fences:

View: https://youtu.be/McXJxYLXq-E?t=50


I used a pretty long level, and as far as I know its pretty darn strait. At the very least, once clamped to the two glued halves of the fence, it should at least keep them from setting with some kind of notable curvature or anything like that.

Regarding a straitedge... I've never used one before. But it sounds like I could use one to check for "true strait" on a cut piece of plywood...or, maybe, the straitness of my fence? I found one that has a one thou accuracy over 24", for $45 on amazon. I do have a dial indicator. It is on a stand with a magnetic base (or at least it was, until it fell from my benchtop to the concrete floor and cracked...) I think I can remove the dial from the stand, but I am not sure how I would use it to help me here. I also have a set of small machinists squares. Three, small, medium and large. They are the most accurate squares I own, as far as I can tell. They aren't capable of measuring more than a few inches along an edge though with the largest one.

Regarding your procedure to check my square's squareness. I think I understand it. I'll give it a try and see how it goes... If I understand correctly, I only need ONE truly strait edge on the piece of plywood, right? I don't have to cut two square edges? If that's the case, then I can do that easily enough. My saw is as strait as I can measure right now with the tools I have, so I should be able to get one known true strait edge. When you say "flip" the square, I assume you mean keep the body (blade?) of the square against that flat edge, and just flip the direction of that (from say top to bottom -> bottom to top orientation?)

 

[Kevin Jenness]

When you say "flip" the square, I assume you mean keep the body (blade?) of the square against that flat edge, and just flip the direction of that (from say top to bottom -> bottom to top orientation?)

Yes.

 

[Jon Rista]

To check a framing square against itself, first get a woodlike panel with a straight edge, at least as wide as the tongue of the square and twice as long as the blade.. Register the square's blade against the reference edge and strike a line along the tongue.with a sharp knife near the panel's center. Flip the square over and compare the tongue with the scribed line. Any difference represents twice the square's inaccuracy relative to "square". To correct the problem, peen the inside or outside corner of the square using a center punch and hammer to expand the metal and change the angle.

Did this...as far as I can tell, the square is dead to nuts strait and square as can be. If there was a discrepancy, its probably in the thousandth or two range or thereabouts, and my eyes, which aren't perfect anymore these days, couldn't detect it. So I think that particular square is good to go. That's the one I've been using since determining my other square is not actually square.

Thanks for the tip!

 

[Holmes Anderson]

I have never had a framing square that was accurate enough to even check a crosscut fence on a table saw. Machinist squares are not particularly expensive and much more accurate than framing tools but 5-cuts with a large sheet is more accurate. The fence adjustments are where things go sideways. Get yourself a sliding table. They are easier to adjust and much better than sleds.

 

[Jon Rista]

I have never had a framing square that was accurate enough to even check a crosscut fence on a table saw. Machinist squares are not particularly expensive and much more accurate than framing tools but 5-cuts with a large sheet is more accurate. The fence adjustments are where things go sideways. Get yourself a sliding table. They are easier to adjust and much better than sleds.

Hence the reason I'm doing the 5-cut method. The square does get me close, but its not perfect. The 5-cut method from the video I linked should be able to get me down to a few thou. I'm working on following @Brian Gustin 's advice with a screw in an adjustable hole. I expect to have this thing aligned today.

As for a sliding table...I've invested a fair amount into this sled now. I don't see changing anything at this point, once the fence is aligned.

 

[Tim Hunter]

Hence the reason I'm doing the 5-cut method. The square does get me close, but its not perfect. The 5-cut method from the video I linked should be able to get me down to a few thou. I'm working on following @Brian Gustin 's advice with a screw in an adjustable hole. I expect to have this thing aligned today.

As for a sliding table...I've invested a fair amount into this sled now. I don't see changing anything at this point, once the fence is aligned.

That's right - the whole purpose of the 5-cut method is to eliminate dependence on a reference instrument such as a square that may or may not be square. Instead, the accuracy of the method is inherent to the process. In fact, once you are successful with the 5-cut method, you can use the cut piece to check your squares.

Tim

 

[Jon Rista]

@Brian Gustin Used a pocket hole screw. Took a bit of trial and error to find a through-hole size that would allow for enough adjustment to the fence, and the right forstner size to ensure the head didn't butt, however I think this will do now.

 

[Mike Selser]

I was at a meeting this morning where a member showed his new jig.

Katz-Moses Jig and Sled Square: Revolutionize Your Woodworking! (Presale)

On Presale: Ships in about 8-12 weeks Jonathan’s Hot Take: The Patent Pending Katz-Moses Jig and Sled Square isn't just a tool – it's a game-changer. It's the sole solution on the market that eliminates the need for the 5 cut method for crosscut sleds, making precision woodworking easier than...

kmtools.com

View: https://www.youtube.com/watch?v=1iMpJl_8Sdo


Not very practical for a lone user but would be great for a club to have to loan out to members.

 

[Jon Rista]

I was at a meeting this morning where a member showed his new jig.
View attachment 74913

Katz-Moses Jig and Sled Square: Revolutionize Your Woodworking! (Presale)

On Presale: Ships in about 8-12 weeks Jonathan’s Hot Take: The Patent Pending Katz-Moses Jig and Sled Square isn't just a tool – it's a game-changer. It's the sole solution on the market that eliminates the need for the 5 cut method for crosscut sleds, making precision woodworking easier than...

kmtools.com

View: https://www.youtube.com/watch?v=1iMpJl_8Sdo


Not very practical for a lone user but would be great for a club to have to loan out to members.

This is really interesting. I was just wondering earlier, if there was some way I could use the kerf in the sled as an alignment reference...

I don't expect to be making another sled for a while, so yeah, $130 more is not exactly cost effective... Still, this seems like a pretty optimal solution.


I think there is some source of flex in my setup somewhere. Its not the runners. I cleaned out the miter tracks, and they run without slop but smooth. I don't think it is the screw anymore now that I'm following @Brian Gustin's recommendation. Maybe the fence itself is flexing? It is only screwed in at the ends right now. Otherwise, I don't know what's wrong. I am down to about 0.010 give or take. I seem to be oscillating back and forth, +/- 0.01 in error. I've run out of wood to test this on. So for now, I'm going to leave it where it is. I'll try to cut some other scrap pieces of wood, and see how the edges line up in various orientations...maybe it will suffice for my shorter term needs.

 

[John Whitley]

I've used the 5 cut method and found it too fiddly. I went back to using a 3 cut method, simpler and equally accurate.

Agreed. This is what I used to square up the crosscut fence on my saw, which is a small sliding table saw. Three cut is a much simpler process.

The other thing I'll add is to make sure that there's ZERO slop or flex anywhere. For a crosscut sled, this could be poorly fit miter slot bars. They should slide freely, but allow no rotation of the sled at all. It's also important that the pivot center you're using when making adjustments remains fixed, with no slop either.

An example, to illustrate the latter point: When I was setting up my (used) saw, I ran into similar baffling problems dialing in square – a total balloon dog of adjustments vs. subsequent square measurements not making sense. (If everything's right with the sled/saw, the process should generally converge, whether using the 3- or 5- cut methods.) In my case, I eventually realized that the crosscut beam's pivot pin was missing a critical spacer washer. The pin is conical, designed to ride perfectly in the matching hole in the outrigger. Instead it was "floating", loose in that hole. Every time I unlocked then locked the crosscut beam while making adjustments, the pivot center had changed! A set of brass shim washers fixed that problem, then the 3-cut method worked as expected.

 

[Mike Selser]

What is your fence made from? Are you sure it is perfectly flat? How are you checking for slop in the runners? The correct way is to push on upper left and lower right corners then on the lower left and upper right corners and see if there is any movement. When checking for slop you can check with the runners fully engaged in the miter slots and also with the sled all the way towards you at the point where you start the cut for a wide board. If the runners fit tightly at the ends but not in the middle you may get some slop when starting the cut. Many commercial runners have adjustment screws or cams at the ends and center and you can get slop when the ends are out of the miter slot if the center is not adjusted properly. This can even be a problem with home made runners if they are attached with countersunk screws. The screws tend to expand the runner and if the expansion is not the same in the center as the ends you can get slop when the ends are not engaged in the slot. There are just so many things that can go wrong!

 

[Jon Rista]

What is your fence made from? Are you sure it is perfectly flat? How are you checking for slop in the runners? The correct way is to push on upper left and lower right corners then on the lower left and upper right corners and see if there is any movement. When checking for slop you can check with the runners fully engaged in the miter slots and also with the sled all the way towards you at the point where you start the cut for a wide board. If the runners fit tightly at the ends but not in the middle you may get some slop when starting the cut. Many commercial runners have adjustment screws or cams at the ends and center and you can get slop when the ends are out of the miter slot if the center is not adjusted properly. This can even be a problem with home made runners if they are attached with countersunk screws. The screws tend to expand the runner and if the expansion is not the same in the center as the ends you can get slop when the ends are not engaged in the slot. There are just so many things that can go wrong!

The fence is made from two 3" tall slices of the same plywood as the rest of the sled. I cut them one after the other from the other half of the 2x4' sheet. I then set it up such that the two faces that I glued together, were effectively "opposites" so that their curvatures counteracted each other. I then plastered them with a thin layer of wood glue each, and clamped them to my long Empire level, which is the longest truly strait thing I have. I don't know what its straitness rating is, its probably not one thou over four feet, but I think its more than close enough. I let that dry for a whole day before I unclamped. The fence is 1 1/2" thick, and its as strait as I had the capability to make it.

Regarding the runners. I bought some pre-cut HDPE strips that were specifically designed to be used as runners for table sleds. They fit perfectly into the slots, and while I could probably fit a 1-thou or maybe a few t hou feeler gauge between the runners and the slot edge, there is pretty much no slop (at least when they are situated so they fill up the whole miter slots).

When I pull the sled out to start cut one for a 5-cut, I'd say a bit over half the sled is off the table. There is a very slight bit of play...in all honesty, that may well be my miter slots, not necessarily the runners? It is just a Ridgid job site saw. My miter slots on my table saw, for maybe 1/4" or so at the end, they flare out slightly. So I can't test at the very ends, as they are actually designed with that flare to help you insert runners end on (rather than top down). Since these are just HDPE strips, there are no adjustment clips. My miter gauge from Incra has adjustment clips, which barely work for the purpose. The Incra miter gauge has some slop. Every time I try to fix that, though, with those adjustment clips (round discs with an angled slice in them...you tighten or losen a screw to expand or contract the discs), the incra will bind up at certain points in the miter slot. So, I had to back them off so the gauge would slide through the full run of the slot. There are actually certain points at which they bind...I suspect that is a SLOT issue, then, not a runner issue? Whenever I use the miter gauge on its own, I always...well, I guess I twist it counter-clockwise. So the end towards my hands, the runner rests against the blade-side (inner side) of the slot, and the far end against the outer side of the slot.

When I screwed the runners into the sled, I actually drilled holes in the runners the size of the thread, not the shaft. I then drilled holes the size of the shaft into the sled. I then countersunk the holes in the runners. So the screws clamp down on the runners, but they are not actually threaded into them, and therefor are not expanding the runners in any way. I also don't tighten the screws so much that they squish the runners...just enough to snug them up. The runners ALSO have been CA glued in place. I cut the runners to size, placed them on top of some washers inside the miter slots, ran some beads of CA glue down each, then sprayed activator on the sled itself. I had pre-aligned the table saw fence and set it at the point I needed it, and was able to use that as a stop, then levered down the sled on top of the runners. I was extremely careful bringing the sled down on top of the runners and their glue. This kept the force nearly strait down on top of the runners for the initial glue-up...and fwiw, I had the runners pushed out to the side of the miter slots away from the blade (although, to be perfectly honest, once the sled was on top of them and the glue was being pushed around, I can't say if they stayed there). I left it that way for a bit, then pulled it up. A slight bit of glue got on the top edge of one of the miter slots on one side, and I had to clean that off. But otherwise, the runners were effectively perfectly set into the slots, and glued to the sled, with about as optimal a procedure I could find. (I did my due diligence watching every table sled build I could find, and some were pretty advanced and fancy sleds, before building this one. So I had a lot of techniques going in, to help me avoid a lot of the common problems, which I think I did.)

When the sled is in the middleish area of the table saw, there is no slop (or rather, not enough to be an issue, I guess...I mean there is a very slight bit). Pulled out enough to fit my piece of plywood for the 5-cut method, I guess there is a slight bit of slop. I now wonder, if the flared edges of the miter slots in the table, might actually be the cause of that... So I guess, I kind of have the opposite problem you described? I have a bit of slop when the sled is pulled out, but none when it is pushed in. I suspect that could still cause imperfect cuts though... Since it seems to be fine when within the middleish range of the table, though....I don't know if there is any way to resolve that. I couldn't really shim anything, as if I shimmed while the sled was pulled out, it would most likely bind up once pushed in.

I did just go out and make a few test cuts. I cut all four sides, making them all square to the fence (as good as it is here), then cut the piece right down the middle. Flipping one side of the two halves vertically, and fitting the cut edges together again, I see no gaps. I took my medium sized machinists/engineering grade squares (I have a set of three, 1.5", 3" and 5") and there might be about a hairs thickness gap just at the top portion (which may be due to that part toughing the blade once the cut was made...), but otherwise the pieces are totally square. Actually, I also just measured each piece top and bottom with my calipers, and the top and bottom actually seem to be within two thousandths of each other. So, I dunno, maybe I am dialed in enough here that this will be fine for most of the work I want to do...

 

[Jon Rista]

Agreed. This is what I used to square up the crosscut fence on my saw, which is a small sliding table saw. Three cut is a much simpler process.

The other thing I'll add is to make sure that there's ZERO slop or flex anywhere. For a crosscut sled, this could be poorly fit miter slot bars. They should slide freely, but allow no rotation of the sled at all. It's also important that the pivot center you're using when making adjustments remains fixed, with no slop either.

An example, to illustrate the latter point: When I was setting up my (used) saw, I ran into similar baffling problems dialing in square – a total balloon dog of adjustments vs. subsequent square measurements not making sense. (If everything's right with the sled/saw, the process should generally converge, whether using the 3- or 5- cut methods.) In my case, I eventually realized that the crosscut beam's pivot pin was missing a critical spacer washer. The pin is conical, designed to ride perfectly in the matching hole in the outrigger. Instead it was "floating", loose in that hole. Every time I unlocked then locked the crosscut beam while making adjustments, the pivot center had changed! A set of brass shim washers fixed that problem, then the 3-cut method worked as expected.

The pivot is a screw at the right hand side of my sled (based on when I stand in front of it like I was using it.) I have not losened that at all. The other end, now, has a pocket screw in it, and the sled has a hole larger than the shaft of that screw, and then I used a forstner to counter-sink so that the screw can clear the table. For my latest adjustments, I just barely losened that screw, left the pivot screw in place without adjustment, and very slightly tapped the swing end of the fence to adjust it. The first adjustment, I placed the feeler gauge, brought up that "pointer" to just touching (without real force, eliminating slop in the feeler), loosened the pocket screw slightly, removed the feeler, tapped on the fence till it met the pointer tip, and tightened the screw. The I removed the pointer (it was clamped in place), and did another set of cuts. That flipped back the other way by +0.012 (originally it was -0.021), so I basically repeated the above, only this time I loosened the screw before the feeler, and used the feeler to force the fence back, and tapped the fence back to take up any slop in the feeler without pinching it. Tightened the screw. Now it was -0.00905. I seem to be suck at about a hundredth accuracy here...except, if there is slop causing problems, then maybe not. What I ended up doing, was adjust it one more time by five thousandths, and I left it.

 

[Brian Gustin]

The pivot is a screw at the right hand side of my sled (based on when I stand in front of it like I was using it.) I have not losened that at all. The other end, now, has a pocket screw in it, and the sled has a hole larger than the shaft of that screw, and then I used a forstner to counter-sink so that the screw can clear the table. For my latest adjustments, I just barely losened that screw, left the pivot screw in place without adjustment, and very slightly tapped the swing end of the fence to adjust it. The first adjustment, I placed the feeler gauge, brought up that "pointer" to just touching (without real force, eliminating slop in the feeler), loosened the pocket screw slightly, removed the feeler, tapped on the fence till it met the pointer tip, and tightened the screw. The I removed the pointer (it was clamped in place), and did another set of cuts. That flipped back the other way by +0.012 (originally it was -0.021), so I basically repeated the above, only this time I loosened the screw before the feeler, and used the feeler to force the fence back, and tapped the fence back to take up any slop in the feeler without pinching it. Tightened the screw. Now it was -0.00905. I seem to be suck at about a hundredth accuracy here...except, if there is slop causing problems, then maybe not. What I ended up doing, was adjust it one more time by five thousandths, and I left it.

I seem to recall that you need to HALVE the difference in thickness as a sled adjustment? Been so long since I did 5-cut (in favor of my modified 3-cut I mentioned) I forget... so if you're .010 out, you need a .005 feeler gauge?

 

[Jon Rista]

I seem to recall that you need to HALVE the difference in thickness as a sled adjustment? Been so long since I did 5-cut (in favor of my modified 3-cut I mentioned) I forget... so if you're .010 out, you need a .005 feeler gauge?

According to the video I linked, with that particular calculation, the result gives you the absolute error (E) at the swing end of the fence. So he used a feeler of that size to make the adjustment.

 

[Brian Gustin]

OK umm, that's where I get my confusion from I guess - couldn't wrap my head around the math when you consider if it is out .010" at 6" of the cut, then you adjust your 16 inch fence by that same .010" didn't make a lot of sense when you think maybe at 6" out it is out .010 but at 16" out it'd be closer to .025", but then I remembered you have to also know the length of the piece you are measuring - That's why I gave up on it for my sleds, as it was too much work since I had to dial it in again every so often that I used the sled because something was shifting out of place, which is when I made my sliding fence that I can also adjust to get more precise miter angles (such as 45 degrees or 67.5 degrees for 8-sided cuts, etc.) and using a carefully prepared length of 6" wide board (2 perfectly parallel edges) to simply make one cross cut then flip it edge for edge and trim off another bit, then measure that, and adjust my fence at the 6 inch point from the pivot. (even works on miters since at the 6 inch width you can calculate the difference in dimension for a particular angle, forgot what that's called since I just have them written down in notebook, and adjust from there)

 

[Tim Hunter]

Yet another thing that no one needs (the KM sled square).

Tim

 

[robo hippy]

One thing about the pocket hole screw stuff, I never use them, ever! It seems that the piece I am screwing into always creeps up just a little bit. That means if you used it on a table saw sled, the sled would move as you screwed it into place. I did see some one gluing up the back stop for a table saw cross cut table, and he glued it up on the bar on the table saw fence rail or what ever it is called. That seemed like a good idea.

robo hippy

 

[Mark Jundanian]

Are you using a regular kerf or thin kerf blade? Thin kerf might have some flex.

 

[Brian Gustin]

One thing about the pocket hole screw stuff, I never use them, ever! It seems that the piece I am screwing into always creeps up just a little bit. That means if you used it on a table saw sled, the sled would move as you screwed it into place. I did see some one gluing up the back stop for a table saw cross cut table, and he glued it up on the bar on the table saw fence rail or what ever it is called. That seemed like a good idea.

robo hippy

My suggestion for pocket hole screw was not to use pocket holes per se - but the screw itself (which some will come with a flat washer as part of the head) - so if you have a flat surface and a hole a bit bigger than the screw shaft diameter, the screw will let you shift a piece with some bit better degree of precision before you fasten it down, and THEN you can screw your fence in place with regular wood screws (the V shaped countersink doesn't always keep it exactly where you need it as you tighten it down it can shift a bit - even a thousandth of an inch, and throw your fence off square) That way you don't have to redrill a new hole with countersink every time you adjust your fence. (and then have it thrown off as you tighten it all down) , once you have it squared up and secured in place , the first (pockethole) screw can be tightened down enough to keep the fence in place while you put the rest of the screws in.. Of course, a regular flat head / sheet metal screw with a decent hardened flat washer can do the job too... but most woodworking shops likely have a few pocket hole screws lying around... and it's easier to work with them having the one piece (screw with flange) instead of two (screw & washer)

 

[Jon Rista]

OK umm, that's where I get my confusion from I guess - couldn't wrap my head around the math when you consider if it is out .010" at 6" of the cut, then you adjust your 16 inch fence by that same .010" didn't make a lot of sense when you think maybe at 6" out it is out .010 but at 16" out it'd be closer to .025", but then I remembered you have to also know the length of the piece you are measuring - That's why I gave up on it for my sleds, as it was too much work since I had to dial it in again every so often that I used the sled because something was shifting out of place, which is when I made my sliding fence that I can also adjust to get more precise miter angles (such as 45 degrees or 67.5 degrees for 8-sided cuts, etc.) and using a carefully prepared length of 6" wide board (2 perfectly parallel edges) to simply make one cross cut then flip it edge for edge and trim off another bit, then measure that, and adjust my fence at the 6 inch point from the pivot. (even works on miters since at the 6 inch width you can calculate the difference in dimension for a particular angle, forgot what that's called since I just have them written down in notebook, and adjust from there)

The math, as I understand it, boils down to the following formula:

A = T-B/S/L*R

Where:

A = Absolute Adjustment to Swing-side of fence
T = Width of 5th cut at top (thousandths)
B = Width of 5th cut at bottom (thousandths)
S = Number of sides; Constant = 4
L = Length of 5th cut (inches, or thousandths, units must agree with R)
R = Radius of swing of the fence (inches, or thousandths, units must agree with L)

I think the key here, is the L and R terms. This is actually a translation, of the error in the cutoff, to the error in the fence. T-B calculates the absolute difference in the width of the top and bottom of the cutoff, which is a compounded error...the four cuts compounded the original error in a single cut, making it larger so it is easier to detect/measure. Divide by four (T-B/S -> T-B/4), to transform that "compounded error" back to the error of a single cut. From there, really, you apply by the term (1/L*R), which is a translation term that converts it from an error in the cutoff, to the error in the fence.

The error, was always in thousandths. Its not say an error in terms of angle, its just an error in terms of offset. The guy in the video I watched, which was from 13 years ago, and I think its the original source for the method (and he runs through the theory and the math in some detail), when he finished his sled build, appeared to use the whole final value in thousandths to find his feeler gauge and used that feeler to either shift the fence in (when the final translated error is negative, you move the swing end of the fence into the sled) or out (when the error is positive, you move the swing end of the fence out away from the sled.) His technique for moving the fence was really simple. He created a "pointer" piece of wood, just a wood with two angled cutoffs on one end, with the point rounded a bit. If he needed to move the fence in (negative error), he would place the feeler against the fence, and touch that point to the fence+feeler. Not with pressure, just touching, no slop in the feeler but it should be easy to slide in/out. He then removed the feeler, shifted the fence until it touched that point. Easy way to EXACTLY (supposedly) adjust the fence by exactly that absolute error amount (i.e. 0.021 thousandths). If he needed to move the fence out (positive error), he would put the pointer in place, just touching the fence. Then loose the fence, insert he feeler, bring the fence in so that the pointer and fence just touch the feeler but not compress it (same as with a negative error), and lock the fence in place.

In theory, at least, it works and should be easy. I guess, in practice, there are a number of sources of potential issues, either slop in the rails, flex in the fence, perhaps flex or slop somwhere else (maybe the fence wasn't screwed down tightly enough for the five cuts), so its not just as simple as it sounds. In the video, after he made his adjustment to his fence, he measured, and it was effectively perfect. I think part of my problem is, the pieces of plywood I bought, are not actually the baltic birch I thought they were (made the mistake of buying from Home Depot, and at the time, we had all those shipping problems...I think someone swapped in cheaper plywood veneered with paper-thin birch wood or something.) I think there is more flex in whatever I have, than I'm used to with real baltic birch plywood.


After the fence is aligned, I don't think you should have to adjust again, unless maybe wood movement affects the fence in such a way that it ends up at an angle again? I guess that could certainly happen. I guess the other possibility is, maybe the fence is shifting with use, if you are pushing on it... That, in fact, lead me to what I think is my own problem, but I think its also easy enough to fix in the long run: My fence is flexing slightly in the middle. Its not screwed down there, and I noticed I was pushing more towards the center, rather than pushing at the ends where each end is anchored with a screw. I suspect, that may be the source of my error.

I also noticed that, since cleaning off the CA glue that got in one of the miter slots, there is a bit of slop. Previously, there was ZERO but it was a bit hard to push the sled. Now there is some, but, the sled moves pretty easily. So that may be another source. I have some ideas for how to fix that.

For the fence, I think what I'm going to do, IF I try to align the fence better (I think its less than a hundredth, if my assumptions are correct it should be fairly close to 5 thousandths, which from a number of videos on fence accuracy, that should be good enough for the vast majority of cuts now), is just make sure I am pushing it from the two ends of the fence where its anchored. Once I know its perfect, I'm going to screw it down along the length to eliminate any flex and hopefully minimize any future movement. The sled has multiple t-tracks to place clamps in, so I don't need to hold the piece of wood for 5-cut myself, I can just clamp it in.

 

[Jon Rista]

Are you using a regular kerf or thin kerf blade? Thin kerf might have some flex.

Its a 3/32" blade. Thinner than full kerf by 1/32"...yes. However, the kerf in the table saw, has not widened throughout my use. I don't think the blade is flexing, at least, not any more than it normally would? I was worried the kerf in the sled might end up too wide, if I had the blade less than perfectly strait, but, its sustained "exactly as wide as a tooth" thus far.

 

[Jon Rista]

My suggestion for pocket hole screw was not to use pocket holes per se - but the screw itself (which some will come with a flat washer as part of the head) - so if you have a flat surface and a hole a bit bigger than the screw shaft diameter, the screw will let you shift a piece with some bit better degree of precision before you fasten it down, and THEN you can screw your fence in place with regular wood screws (the V shaped countersink doesn't always keep it exactly where you need it as you tighten it down it can shift a bit - even a thousandth of an inch, and throw your fence off square) That way you don't have to redrill a new hole with countersink every time you adjust your fence. (and then have it thrown off as you tighten it all down) , once you have it squared up and secured in place , the first (pockethole) screw can be tightened down enough to keep the fence in place while you put the rest of the screws in.. Of course, a regular flat head / sheet metal screw with a decent hardened flat washer can do the job too... but most woodworking shops likely have a few pocket hole screws lying around... and it's easier to work with them having the one piece (screw with flange) instead of two (screw & washer)

The pocket hole screw was a good idea. I originally was going to use a washer, but, I think that would have been a bit of a pain in the butt. Having that flat part integrated into the screw head just keeps things simpler. I prefer simpler, whenever I can get it.

 

[Brian Gustin]

After the fence is aligned, I don't think you should have to adjust again, unless maybe wood movement affects the fence in such a way that it ends up at an angle again?

Real trouble with mine is a combination of cheap table saw (A Skil portable jobsite saw I got on sale for $299) with its aluminum table top and very limited size, combined with the sled itself - even though it is Melamine (countertop MDF) and fence well fastened, every so often it is no longer cutting square - I think partly the tabletop of the saw is actually warping (I do have a bit of hump in a couple spots that actually causes rip cuts to not be perfectly square edge to face in the middle of the board) and changes with heating/cooling of the seasons (Though maintaining shop at 40 degrees overnight in winter, then heating up to 64 for the 5 to 7 hours I may spend out there on any given day) resulting in the sled always goes out of square (and never the same direction) - after the first 2 sleds I made (and locked down and glued) I just said the hell with it and made a fancier sled that can also do miter angles by routing the slot for a fence bolt so I can swing the fence from anything like 92 degrees down to around just over 35 degrees... (the miter guide that came with saw was practically useless anyways) so my 2 cut (technically 3 - I joint the board long edge then rip to 6 inch wide using a rip sled I made to deal with that hump in the saw table top) to fine-tune for square works fairly well for me as I am measuring at the same 6 inch dimension for both the offcut and the fence, and usually get virtually perfect square cuts - when I am doing flat work, I often get perfect precision with a shooting board anyways and beyond that "pretty durn close" is usually quite suitable

Eventually I *MAY* decide to replace that table saw with something more robust (Thinking SawStop) but for the little amount of actual table saw cuts I need to do (most of them are rough cuts, as I am transitioning most of my flatwork into hand tooled work anyways) I may not even bother as I gain skill with hand tool work (handsaws, hand planes, etc, I may eventually replace or stop using most power tools, leaving just a lathe and drill press and cordless drill, maybe I'll keep the power sander as it can be handy sometimes, but hand scraped finish with a card scraper is superior to even sanding to 600 grit) Only reason I can think of that I might get a new / better table saw is if I decide to do a deep dive into segmenting (I've done SOME, but don't really have the patience or design skills to do much of my own designing) - in which case I'd want a better wedgie sled (Which I might as easily build one for a bandsaw, and do away with table saw at all..)

 

[Jon Rista]

@Brian Gustin Ah, yeah, I can see the potential issues with a Skil. Honestly, the Ridgid has its own issues. The miter slots are not perfect. There are some binding points in them that make using my Incra miter gauge difficult some times. The riving knife is also real hard to keep aligned with the blade. I'm sure there are other issues I haven't even discovered yet, I'm rather new to this (even though I bought the saw back in...oh, I think 2022) and only recently have I been using it more than very occasionally. I guess, you gotta start somewhere, though. I have no room for a Saw Stop. Even their smallest one. Now that Saw Stop's patents have expired, though, I am hoping Bosch brings back their saw with safety tech. It is more compact, and I might actually be able to fit it. Heck, now that Saw Stop's patents have finally expired...I hope that saw safety tech just explodes and finds its way into every saw on the market... That might bring the cost of Saw Stops down a bit...they are really nice saws.

I suspect, I may find that my saw has problems with heating and cooling too. Its still relatively cool, been in the 50s the last couple fo days. Once it gets up to the 80s consistently, maybe I'll find some new problems. So with your sled...your fence itself, is what you swing to change the cut angle? Do you have any photos of that?

I put three T-tracks and two miter slots in my sled here. I had most of the mateirals from years before. I bought the Incra track for the fence, then the micro-adjustable stop block. Overall, its probably close to $200 worth of materials. The 4' long miter+ttrack was fairly expensive. I also had a 4' long t-track. Together those were, I think, $96. The stop block was $30. The piece of plywood, despite NOT being baltic birch (or being whatever it is, maybe cheap baltic?) was $48. The Incra track, I think, was around $30. I had a bunch of clamps and hold downs already. Oh, the material for the runners was I think $30, so I guess the total build is over $200? The tracks I had bought a while ago, though, and the plywood was from 2022. So the cost was spread out, and, technically, the plywood ($100 worth, two sheets) has actually made a bunch of different sleds and jigs so far. In any case...hmm, I actually hope this could be made compatible with another table saw, just by changing the positions of the runners, I guess. Man, nothing is cheap anymore. Remember when a 2x4' slab of plywood was in the $20 range??? :O

FWIW, I am amazed at how skilled some woodworkers are with their tools. I watch a lot of woodworking videos and shorts, and I honestly don't know how some of these guys are able to PERFECTLY follow cut lines drawn onto wood, both in the front and the back of the cut (I always screw up the back!) Perfect cuts. They always leave just a little bit, so they can then use a hand chisel to remove the tough sawn surface, leaving a PERFECT surface behind. Its amazing work. LOT of work, but amazing. If you master that skill, you have my respect! I'm nowhere near that level. I've only really turned so far, and my health has limited much of what I've been able to do there. I'm trying to expand into making other kinds of boxes, and that's been slow, but also all with power tools. I also am trying to expand into the segmented turning space. But, I haven't even thought about going in for all manual hand tool work. Maybe some day...

 

[Tim Hunter]

Here’s the correct math for the five-cut method:

A=((T-B)/4)*(R/L)

Tim

 

[Brian Gustin]

. So with your sled...your fence itself, is what you swing to change the cut angle? Do you have any photos of that?

Yep. I find I actually need to build a new sled now but going to do it up the same way - Evidently while it was stored in the back room where I stashed it to put it out of the way, a rough cut board fell over and cracked it, I'll see if I can remember to pull it out and grab a picture, but yeah - I drill a through hole in the pivot end of the fence just far enough inside of the saw kerf to fit through a bolt for it to pivot on, and another at the other end of fence at some convenient point where I decide to put the knob, (in a drill press to drill holes square to the fence) then drill through the sled itself where fence is to be located, flip sled over to the side runner will be on and stick trammel with router and 1/4 inch bit using the pivot side as trammel pivot line up with the swing hole and route a perfect arc to get my range of adjustment, then a 1/2" straight bit in same router setup to cut a recess just a touch deeper than the carriage bolt head height following the same arc - then just a carriage bolt up through sled and fence and a lock knob on top. that way I can adjust my fence to pretty much any angle I need to cut, and I can dial it in pretty precisely.

I'll see if I can remind myself to get some photos tomorrow when I go out to the shop... I've already got some plans in mind to improve on it for the new sled I'm making (Just waiting for the sled runner to come from amazon ( https://www.amazon.com/Aluminium-Slider-Woodworking-Fixtures-Router/dp/B091Q78CK8 ) which may help vs the jury rigged one I have now.