Tailstock Setover Adjustment (was Alignment)

Re: Alignment

I don't know if this will help any but trying to access,for me sometimes I can read it and still not get it,so I will read it several times when someone gives and answer to one of my questions.Either before or after I will search Youtube to see what I can find,sometimes it helps me to word my questions better.So here is what tubelcain has to say http://www.youtube.com/watch?v=WLXL3cdnbpM
-----I love this place---kroll
 
Re: Alignment

The TS has a bigger diameter than the HS end. This means the TS end did not get cut as much as the HS end therefore, you need to move the TS end toward you now. That will move the work closer to the bit to take off more material. Obviously, the goal is to position the piece so that you don't get a taper. Subtract the two diameters and divide the result by two. That's how far you must move the TS toward you. In this case 0.002". BTW, it's not easy to make those tiny adjustments. You will need to chase this back/forth a few times.

What this is really doing, is aligning your TS. Theoretically, once aligned, it should be aligned at all distances from the chuck but, this is most often not the case.

FYI: I'm building a new TS for my lathe; the reasons of which are many but one, is to include a fine adjustment of this sort.



Ray

cdhknives said:
Okay, how do I tell if it is a up/down (wear) or left/right (can adjust) alignment issue?

View attachment 56733
Click to expand...
 
Re: Alignment

Oh, I can't see in the picture how you're holding the piece... still using a jawed chuck or turning w/a dog? How we proceed and what we can learn from the results are different depending on how the work is held.

Ray
 
Re: Alignment

Easy answer on this one my friend... Just keep those ridiculously large dogs as encouragement/desire to one day get a lathe big enough to use them.


Ray

itsme_Bernie said:
I use them too- but always the smallest I can use on a particular project. But I haven't really used them at very high speed.

I got a hood of some ridiculous size ones someplace, that won't even TURN on my 10L! Hah hah- still thinking (for a little while longer) that I might find some use for them before selling them for the mere $5 I could probably get.

Bernie
Click to expand...
 
Re: Alignment

cdhknives said:
Okay, how do I tell if it is a up/down (wear) or left/right (can adjust) alignment issue?

View attachment 56733
Click to expand...

cdhknives,

Here is a piece that I wrote on the Yahoo Atlas_Craftsman list about a year ago on the effect of tailstock height error. I still haven't gotten around to running the numbers to confirm my added comment at the bottom of the piece. But thinking about it for a while tonight, I still think it's true. In any case, the answer to your question above is that you can't without some other method of measuring.

***********
To give a feel for the actual magnitude of errors a small vertical tailstock to
headstock error actually makes in finished diameter of parts turned between
centers, especially compared to front-back offset error, here are some simple
hard numbers.

Suppose the following:

Bed is straight and level in both planes and carriage travels in a
perfectly straight line parallel to lathe axis in both planes.
Cutter is perfectly on-center at headstock end of workpiece.
Workpiece diameter is 2.00000" (1.00000" radius, makes the calculator input simpler).
Workpiece length doesn't matter (this isn't a supposition, but a fact that
needed to be mentioned here somewhere).
Tailstock is perfectly on-centerline front to back (+/- 0.00000").
Tailstock is 0.01000" high or low (gross error even on a 60 year old Atlas).
Cutting pass is normal (right to left).
Cutter is advanced against workpiece at tailstock end to perfect touchup
(0.00000" cut).
Cutter is ideal (doesn't care about angles between its surfaces and
workpiece) and material is ideal (totally insensitive to depth of cut problems).
The vertical error at touchup at the TS end is 0.01000" (given).

The touchup point at TS end is 0.57297 degrees (ARC SIN 0.01000) around the
workpiece from the actual front of the workpiece.
The vertical error at the HS end is 0.00000" (given).
The cut radius at the HS end is 0.99995" (COS 0.57297) or a cut at the HS
end of 0.00005"

So the new diameter at the HS end is 1.99990" (from 2.00000"). Remember
that this is on a 2" diameter workpiece. However, as the workpiece diameter
decreases, the error increases significantly. For a 1" diameter workpiece,
the cut error is 0.0002" for a diameter error of 0.0004" and for a 1/2"
diameter workpiece the numbers are 0.0008" and 0.0016". So, for small angles,
the error quadruples as the diameter halves.
(added) For a 3/4" diameter workpiece,the cut error is 0.0004" for a diameter
error of 0.0008".

It seems intuitively obvious although I have not run the numbers that if the
tailstock setover is adjusted using the "turn a test piece" method instead of
the precision test bar method that it will compensate for
any height error when you are turning a workpiece of the same diameter as
you used to adjust the setover. But only partially so if the diameter is larger or smaller.

All figures rounded to five places and it is assumed that HP's small-angle
calculations are good to better than five places.

*************

Robert D.
 
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Re: Alignment

+1 on wa5cab's words here... The up/down aspect of the tailstock has virtually no measurable impact on cutting diameter. If it's up/down by several thou, it only makes a difference when you're trying to drill a hole. None of my mics can reliably read past 4 decimal points.


I too wrote-up a mathematical explanation in a different web site several years ago. Doubtful I can find it now.

If you distrust or cannot follow wa5cab's treatise then just consider that for many reasons, the whole compound, carriage and tool bit all jiggle up/down several thou as it travels -yet, shafts come out perfectly round all the time.


Ray


wa5cab said:
cdhknives,

Here is a piece that I wrote on the Yahoo Atlas_Craftsman list about a year ago on the effect of tailstock height error. I still haven't gotten around to running the numbers to confirm my added comment at the bottom of the piece. But thinking about it for a while tonight, I still think it's true. In any case, the answer to your question above is that you can't without some other method of measuring.

***********
To give a feel for the actual magnitude of errors a small vertical tailstock to
headstock error actually makes in finished diameter of parts turned between
centers, especially compared to front-back offset error, here are some simple
hard numbers.

Suppose the following:

Bed is straight and level in both planes and carriage travels in a
perfectly straight line parallel to lathe axis in both planes.
Cutter is perfectly on-center at headstock end of workpiece.
Workpiece diameter is 2.00000" (1.00000" radius, makes the calculator input simpler).
Workpiece length doesn't matter (this isn't a supposition, but a fact that
needed to be mentioned here somewhere).
Tailstock is perfectly on-centerline front to back (+/- 0.00000").
Tailstock is 0.01000" high or low (gross error even on a 60 year old Atlas).
Cutting pass is normal (right to left).
Cutter is advanced against workpiece at tailstock end to perfect touchup
(0.00000" cut).
Cutter is ideal (doesn't care about angles between its surfaces and
workpiece) and material is ideal (totally insensitive to depth of cut problems).
The vertical error at touchup at the TS end is 0.01000" (given).

The touchup point at TS end is 0.57297 degrees (ARC SIN 0.01000) around the
workpiece from the actual front of the workpiece.
The vertical error at the HS end is 0.00000" (given).
The cut radius at the HS end is 0.99995" (COS 0.57297) or a cut at the HS
end of 0.00005"

So the new diameter at the HS end is 1.99990" (from 2.00000"). Remember
that this is on a 2" diameter workpiece. However, as the workpiece diameter
decreases, the error increases significantly. For a 1" diameter workpiece,
the cut error is 0.0002" for a diameter error of 0.0004" and for a 1/2"
diameter workpiece the numbers are 0.0008" and 0.0016". So, for small angles,
the error quadruples as the diameter halves.
(added) For a 3/4" diameter workpiece,the cut error is 0.0004" for a diameter
error of 0.0008".

It seems intuitively obvious although I have not run the numbers that if the
tailstock setover is adjusted using the "turn a test piece" method instead of
the precision test bar method that it will compensate for
any height error when you are turning a workpiece of the same diameter as
you used to adjust the setover. But only partially so if the diameter is larger or smaller.

All figures rounded to five places and it is assumed that HP's small-angle
calculations are good to better than five places.

*************

Robert D.
Click to expand...
 
Last edited by a moderator:
Re: Alignment

Ray C said:
Oh, I can't see in the picture how you're holding the piece... still using a jawed chuck or turning w/a dog? How we proceed and what we can learn from the results are different depending on how the work is held.

Ray
Click to expand...

Neither. I took the chuck off and installed a dead center. For the very light cuts needed for this operation it had sufficient grip to drive the rod without a dog.
 
Re: Alignment

OK... What you're doing then, is a tailstock alignment test. As mentioned earlier it takes a few tries and sometimes, all you need to do is unlock the ram and relock it -and that will move things enough to make a change. Also, if you trust your ways and carriage (which is yet to be determined) you can mount a dial indicator to see how much of a change you're making.

The simple act of locking/unlocking the ram or overall tailstock clamp can move things a good bit. The lock-up method and way configuration are a couple of the critical aspects of lathes. You are getting into the meat of things...

Ray


cdhknives said:
Neither. I took the chuck off and installed a dead center. For the very light cuts needed for this operation it had sufficient grip to drive the rod without a dog.
Click to expand...
 
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