Aligning Table Saw Sled Fence - Five Cut Method

[Jon Rista]

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

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

Tim

That's the same math. Just organized with different grouping. I actually should have at least grouped the T-B , but the rest is the same.

A = (T-B)/4/L*R
  = (T-B)/4 * 1/L * R
  = (T-B)/4 * R/L

You are right, the T-B needed parens (order of operations/precedence), but the rest should just follow standard rules. If you divide by L first, or multiply by R then divide by L, or divide R by L first then multiply, the result is the same.

 

[Jon Rista]

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.

Yeah, if you manage to dig it out, share some photos. What do you do about the blade cut into the fence...if the fence swings around, would the blade eventually chew that central part up? (This is actually a small concern of mine, that over time, the fence will end up getting chewed up at the point where the blade slices it... However, I was also thinking, I would ONLY use it in 90 degree orientation, and never angle the blade. I'd probably build a more advanced sled with replacable clearance plates and maybe fence plates, so that I could angle the place if I wanted to, and not have to rebuild the sled every year or something like that.)

Regarding those runners...wow, $11!? I think I spent over $30 on the HDPE, and it can't be adjusted for optimal fit in the miter slots. I may have to pick a couple of those up myself...

 

[Tim Hunter]

That's the same math. Just organized with different grouping. I actually should have at least grouped the T-B , but the rest is the same.

A = (T-B)/4/L*R
  = (T-B)/4 * 1/L * R
  = (T-B)/4 * R/L

You are right, the T-B needed parens (order of operations/precedence), but the rest should just follow standard rules. If you divide by L first, or multiply by R then divide by L, or divide R by L first then multiply, the result is the same.

You’re trying to do the same thing, but the order of operations will foul your proposals. The parenthesis's are needed to be correct.

Tim

 

[Kevin Jenness]

That's the same math. Just organized with different grouping. I actually should have at least grouped the T-B , but the rest is the same.

A = (T-B)/4/L*R
  = (T-B)/4 * 1/L * R
  = (T-B)/4 * R/L

You are right, the T-B needed parens (order of operations/precedence), but the rest should just follow standard rules. If you divide by L first, or multiply by R then divide by L, or divide R by L first then multiply, the result is the same.

This is what I meant about the 5 cut method being fiddly. I kept getting confused and adjusting the fence in the wrong direction. The 3 cut method provides an intuitively obvious visual of the magnitude and direction of the fence correction required even to a foggy brain like mine.