For you physics experts......why is this?

[odie]

I can take pointed centers mounted into the #2 Morse tapers of my spindle and tailstock and bring them together......the points match perfectly, so my lathe alignment is right on the money.

When I initially mount a bowl to true it up, many times it's between a faceplate on the headstock side, and a revolving center on the tailstock. I usually mount the bowl on the headstock first, and turn on the lathe at slow speed to bring the revolving center to bear. When I do this, I almost never drive the point without making a tiny inscribed circle by the point of the revolving center before I crank it down.

It always runs fine, but it seems to me that even if the top and bottom of the bowl aren't in the exact same plane, the exact center will have no wobble, even though it might have quite a bit of wobble at the rim......thus the revolving center point shouldn't make a little circular pattern when it first makes contact.

I was wondering if anyone has a good explanation for this......?????

otis of cologne

 

[Ed_McDonnell]

How about this explanation. Maybe the bed of your lathe is bent. When you bring the tailstock and headstock together they line up. Move the tailstock further away and the bend in the lathe moves them out of alignment. Then again it could be something else............

Ed

 

[Ken Grunke]

Otis, forgive me if I misunderstand your question but there probably is no such thing as perfectly aligned centers. It's all relative--some lathes are just better than others. Your lathe has only a tiny bit of misalignment, so the tailstock point has to plow a tiny little off-center hole first before you can drive it into the wood.
On a cheap lathe such as a Jet 1236 which has relatively quite a bit of misalignment (actually slop in both the headstock and tailstock), the point will plow a bigger hole and will leave a little dimple in the center if the alignment is off by more than a 64th or so. My Jet 1236 is off by almost 1/8" unless I loosen the headstock and whack it over until the little dimple made by the tailstock lines up with the point. Then I can achieve perfect alignment

 

[Mark Mandell]

Odie,

You're comparing different "centers" that rarely match. When you use the two points, you're seeing that the 2 morse tapers are aligned and the 2 centers are set properly. When you use the faceplate, you've abandoned the taper alignment and are using the outside threaded surface of your spindle as the reference. The threads on your faceplate may not mate perfectly with those on your spindle, or the faceplate may not be machined to a tolerance that places the face of the plate exactly parallel with the shoulder of your spindle.

I wouldn't worry about it. You're turning wood, not parts for a watch.

 

[Randy Rice]

"You're turning wood, not parts for a watch."

Mark, this should be at the top of every woodturning forum!

 

[odie]

Ed......that's a distinct possibility....a creative way of looking at it!

Ken....yep, I think you got a handle on the question. 1/8th" off! Wow, that seems like a lot to me. I have no way of measuring the offset of my Woodfast, but the alignment is as good as it can get by "eyeballing" it. You're right that there's probably not any lathe that's in absolute perfect alignment. In that respect, I guess I'm wrong to have stated mine was so. Just how much my alignment is off, is hard to say, but that probably is the best explanation of the "tiny circle" the center is inscribing in the workpiece. Thanks for bringing me into focus on this.

Mark....I'd say you're correct in suggesting my thinking was a little off by my assuming if the two centers mounted in the Morse tapers match, my alignment would be, too......but, it wouldn't matter if the threads of the spindle revolved to true center or not, I would think. This is somewhat along the lines of an eccentric chuck.....the center is where it is, and isn't determined by how, or where the workpiece is held. Seems to me the true axis of the turned piece would actually be determined by the bearings themselves........Since one side of the bearings would be fixed by the lathe housing, while the other side would have a tolerance variable determined by the bearing's precision in construction. Wouldn't you think? This probably isn't enough of a variable to account for the "tiny inscribed circle". As small as it is, it's probably larger than the few thousandths that could be accounted for by thinking along the terms you are.......but, who knows.....I've been known to be wrong about a lot of things!

BTW: I'm not sweating this at all. I've been using this Woodfast lathe since 1992, and never saw it as being a problem......only reason I brought it up is I thought it would make an interesting discussion......and it is!

otis of cologne

 

[Mark Mandell]

Odie,

The taper mounted points on my stubby match precisely when I use my taper mounted drive center; match , not orbit one another.

The points also match when I use my spin-on drive center; IF I'm careful to properly seat it up tight to the spindle shoulder.

But put an inexpensive faceplate on to mount the wood and my TS center point draws that same little circle of which you speak.

 

[odie]

Odie,

The taper mounted points on my stubby match precisely when I use my taper mounted drive center; match , not orbit one another.

The points also match when I use my spin-on drive center; IF I'm careful to properly seat it up tight to the spindle shoulder.

But put an inexpensive faceplate on to mount the wood and my TS center point draws that same little circle of which you speak.

Mark: To my thinking, it wouldn't matter if a faceplate is precision, or not, because that doesn't determine the center of the work being held in relation to the axis of the spindle.

If your reasoning were so, then how would you account for an eccentric chuck? The workpiece could be way off center, but it's center is in relation to the spindle axis......not how it's being held to the spindle.

otis of cologne.

 

[odie]

I just went out to the shop and made a startling discovery!

As a little background.....I've been using step pulleys on my Woodfast lathe for the past 15yrs, and up until last October. At that time, I converted my lathe to a variable speed. I could not perform the check I just made using the step pulleys....because the slowest speed I could go was 360rpm.....too fast for the following check.

Anyway, I put every #2 Morse taper attachment I had in the headstock spindle Morse taper (seven or eight of them), and ran them at a very slow speed. Doing this, I was able to see the runout of each center point. The only one that seemed to run perfectly true (or, at least what can be determined by eyeballing it) was an economy revolving center! All the expensive steb centers, revolving centers, drive center, etc., had some detectable runout! This goes to show that you may not always get what you pay for!!!!

Knowing the aforementioned only confirms that putting attachments into, or onto the headstock and tailstock to see if the centers match, isn't what I'd now call a confirmation of lathe alignment between headstock and tailstock. It's close, but not conclusive.....so, I've changed my mind about that!

Knowing all that's transpired in this thread, I'm concluding that kengrunke's post, as simplistic as it is, gives me the most thought provoking information to make some conclusions about this matter of the "tiny circle". The only conclusion that fits the evidence, is my lathe does, for sure, have a very small bit of misalignment.

And all of this boils down to what?.......big deal, so what! I ain't makin' no watch parts. Ha!

otis of cologne

 

[Mark Mandell]

Odie,

I can only report what I've observed; no physics in what I say. I do know, however, that if I true up the center point of the wood before I engage the TS center, the little circle seems to disappear.

Since my wood turns true, I'll leave the physics to others.

 

[Dale Miner]

A trio of possbilities.

There are two different alignments, The offset, that you can detect by bringing the two points together, and the angular, that is difficult to detect without some measuring equipment.

(1) If the vertical, and horizontal offsets are correct with the two points together, but the angular alignment of the spidle to the bed is off, then as the tailstock is moved away from the headstock, the offset of the two points will increase. 1/10 of a degree is about .0017 in/in. So if the angular was 1/10 of a degree off, and the tailstock is moved 10 inches, the offset will now be .017 in., leaving a .034 in. inscribed circle.

(2) Any flex in the spindle and or faceplate from the overhanging weight of the blank will result in an angular sag of the centerline of rotation. Clearance in the spindle bearings will yield the same result. The angular sag of the centerline will result in an offset at the live center point. If this is the case, the tailstock center point should be inscribing the circle at or near the top of the circle.

(3) If the bed is in a twist, if will produce the result that you desribe. The tailstock point will generally be off to one side when it inscribes the circle.



Later,

Dale M

 

[odie]

Odie,

I can only report what I've observed; no physics in what I say. I do know, however, that if I true up the center point of the wood before I engage the TS center, the little circle seems to disappear.

Since my wood turns true, I'll leave the physics to others.

OK, Mark.......It was good to get your input on this......made me do a lot of thinking about things that have acquired some cobwebs over the years!

What you say about "truing up" the center point makes a lot of sense on the reasons why the "tiny circle" exists for me.

No matter who's right or wrong, it doesn't matter that much.......it's just a casual discussion, and really doesn't matter that much in the scheme of wood lathy things! What is, is......and what works, works!

otis of cologne

 

[57_T-Bird]

add a shim...

I've noticed the similar mis-alignment when using a chuck and wanting the tailstock support.

Cured the problem by slipping a 0.029" shim underneath the front rail of the tailstock.

A feeler gauge would work for the trial and error method to determine the correct thickness and which rail to shim.

The one I use is steel and about a foot long by 1/2" wide. Came from auto supply store. The length makes it easy to slip under the tailstock when needed and being of steel instead of brass makes it last.

I don't always use it. Doesn't seem that its needed all the time. But occasionally its a quickcure for that (near) perfect alignment.


T-Bird

 

[MichaelMouse]

Bit of a dance around what I'd say, so I'll say it myself. Take your tailstock, loosen the cam, and see how much lateral travel it has. Has to have some, or it'd be almost impossible to move up and down the bed. With my old 3000 I have the tail adjusted so the entire is aligned best butted tight in the direction I turn to lock. Imagine a bit of squeeze L or R as you tight may take care of any slop in the Woodfast.

Another thing you can look at is the quill. Any basic misalignment at the tailstock will grow in absolute dimension as the quill is extended. Larger radius, after all, gives longer chord.

The other things about threads versus tapers are also possible, but much less likely. Others who have rotating heads on the lathe need first to align their head to the tail rather than vice-versa.

 

[Joe Greiner]

What they all said, especially tailstock running clearance. But also, any penetration into material with non-uniform mechanical properties (such as wood) tends to dive along the path of least resistance. The initial penetration may be dead on, but further penetration can go awry. FWIW, Machinery's Handbook, 24th edition, devotes four paragraphs to "Accuracy of Drilled Holes," with about a dozen factors to consider.

Joe

 

[odie]

Take your tailstock, loosen the cam, and see how much lateral travel it has. Has to have some, or it'd be almost impossible to move up and down the bed. With my old 3000 I have the tail adjusted so the entire is aligned best butted tight in the direction I turn to lock. Imagine a bit of squeeze L or R as you tight may take care of any slop in the Woodfast.

Thanks MM, and that's exactly what I did.

By taking up the slack in the tailstock to bed mounting, I was able to lessen the runout. This is what I do each and every time I install a revolving center, or anything into the Morse taper of the TS. I have in the past, however, taken up the slack by rotating the TS in a clockwise direction in the bed rails. As you suggest, it might be better to readjust my thinking on this, and take up that slack in a more side-to-side manner.......that way the quill will probably remain in more of a constant state of alignment as it's extended.

Although, by eyeballing it in a static way, the runout appears to be nil, the fact that the "tiny circle" exists when bringing a revolving center to bear is testament to it's existance. However, all said and done......we are talking about such a small amount of runout, that it has never had any measurable, or noticeable effect in any of my turnings. If it's as much as .010", I'd be surprised.

I suppose, in this particular instance, we are approaching the realm of considering the validity of theory, as opposed to practical application.....

Thanks to all of you for your input on this. It has been inspiration for me to make corrections in my thinking and procedures that may not make a difference in my turnings, but can only help to make the mechanical precision of my lathe just a tiny bit better overall.

otis of cologne

 

[Frank Kobilsek]

Odie

Its not Physics, its geometery. You problem is that you have the wrong reference book out.

Frank

 

[john lucas]

Even dirt on any of the surfaces could also cause the problem. If you have dirt between the faceplate and spindle it won't seat absolutely flush. Dirt underneath the tailstock can throw that off as well as dirt on the surface that touches the side of the rail. Dirt in the Morse taper can change how it seats. Man I need to clean my shop.

 

[Ron Sardo]

I've noticed the similar mis-alignment when using a chuck and wanting the tailstock support.

Cured the problem by slipping a 0.029" shim underneath the front rail of the tailstock.

A feeler gauge would work for the trial and error method to determine the correct thickness and which rail to shim.

The one I use is steel and about a foot long by 1/2" wide. Came from auto supply store. The length makes it easy to slip under the tailstock when needed and being of steel instead of brass makes it last.

I don't always use it. Doesn't seem that its needed all the time. But occasionally its a quickcure for that (near) perfect alignment.


T-Bird

While doing this might center the two points, the tapers will not be aligned because one will now have a slope.

 

[Mark Mandell]

Even dirt on any of the surfaces could also cause the problem. If you have dirt between the faceplate and spindle it won't seat absolutely flush. Dirt underneath the tailstock can throw that off as well as dirt on the surface that touches the side of the rail. Dirt in the Morse taper can change how it seats. Man I need to clean my shop.

Learned that the hard way. When my Stubby arrived I found a tiny burr on my tailstock taper that threw the points out of alignment by 1/16". Bought a #2 MT reamer, and gently gave it a couple of turns by hand. Problem solved and the (then) needle points met precisely. I since then I use one of the urethane Tapermate cleaners regularly.

 

[odie]

Odie

Its not Physics, its geometery. You problem is that you have the wrong reference book out.

Frank

Ha.....that's the least of my problems!

otis of cologne

 

[waltben]

I'm still amazed how folks can be worried (not you, Odie) about these things, when we aren't making watch (or rocket) parts. Early on I found one of my new and expensive white painted faceplates was off center about 1/16". Don't know really why I obsessed with this, it just got me more off center than it was. Once I used the thing a couple times, I realized that wherever the wood is in relation to the lathe's centerline, once you begin turning it, it will become aligned. Since then, I bought a bunch of Bill Noble's welded up nut and washer faceplates (and they've got a whole bunch of run out!), and use them for anything 10" and under. It's great being able to mount up 6 to 12 blanks in a couple hours and then spend a week turning without worrying about a second mortgage for machined ones.

 

[Mark Mandell]

I bought a bunch of Bill Noble's welded up nut and washer faceplates (and they've got a whole bunch of run out!), and use them for anything 10" and under. It's great being able to mount up 6 to 12 blanks in a couple hours and then spend a week turning without worrying about a second mortgage for machined ones.

I use Bill's "plates" for all of my vacuum and jamb chucks. Once their working surfaces are trued up on the first spin, any original wobble is either negated or rendered irrelevant.

 

[john lucas]

Walt When you start building things from seperate parts often using the tailstock to bore or help hold things you start having missalingments. So the more accurate it is the closer these parts fit. I take flak from a machinist friend because I measure my tenons and such to .001 inch. He says wood moves more than this. It does indeed but if you shoot for that kind of accuracy everything fits better the first time. It can move all it wants later. Now seriously I don't try for .001" I just try to get as close to that as I can when I'm fitting things. I probably get as close as 5 to 10thous most of the time.

 

[MichaelMouse]

It's great being able to mount up 6 to 12 blanks in a couple hours and then spend a week turning without worrying about a second mortgage for machined ones.

Even with the dollar in the toilet you can get a pin chuck from www.bestwoodtools.com for $70. It's centered, it removes for drying, and it recenters once the hole is re-punched on a dried piece. Of course it takes less than five minutes to mount up a blank, so you'll have time for a coffee break.

 

[waltben]

$70 for one? I'm talking about five for $25 for my mini and five for $39 for my Stubby (I drill the holes). See http://www.wbnoble.com/ for details.

 

[Ron Sardo]

Talking about pin chucks, here is a great how to on making them yourself

Pin Chuck

 

[Malcolm Smith]

May have responded to a similar post somewhere before. A lot of lathes are really spindle lathes that are adapted for bowl turning. Part of this is a rotating head. An inexpensive lathe I had had such a poor locking mechanism for the rotating head that even if one took the trouble to align the headstock and the tailstock, it wouldn't stay aligned. The Oneway lathe I have does not have a rotating headstock and the alignment is excellent (thank you Oneway). In fact, the lathe came with a document certifying this.

Malcolm Smith.

 

[Charlie Knighton]

reamer

Bought a #2 MT reamer, and gently gave it a couple of turns by hand. Problem solved and the (then) needle points met precisely. I since then I use one of the urethane Tapermate cleaners regularly.

thank you Mark, i received my taper mate this week, i now use it before starting turning, right after i check the moisture % of the wood for the
8th time :cool2:

 

[Mark Mandell]

Whoa!

thank you Mark, i received my taper mate this week, i now use it before starting turning, right after i check the moisture % of the wood for the
8th time :cool2:

You're using the TaperMate brand rubber cleaner or a taper reamer?

Use the green rubber cleaner all you want, but the reamer will get you in trouble fo sho by using it that much. The steel reamer is to remove galls and high spots on the female tapers' surfaces; it's not a cleaning thing at all. Every time the reamer is used it removes metal, so you can wreck your spindle or TS quill in short order by over use. I've had my reamer for 4 years, I've used it twice in all that time.

OTOH, the TaperMate (which looks just like a reamer) is to remove dirt and dust on those surfaces. That I use every time I remove or insert a taper tool.

mm

BTW you're very welcome

 

[Charlie Knighton]

green

Use the green rubber cleaner all you wa

thats what i bought, did not see the other :cool2:

 

[Mark Mandell]

thats what i bought, did not see the other :cool2:

The Other:

http://www.use-enco.com/CGI/INSRIT?PMAKA=891-4730&PMPXNO=3904656&PARTPG=INLMK3