On Tuesday, February 25, 2014 1:04:15 PM UTC-5, Cydrome Leader wrote:


I went ahead and centered the pipe in a 3 jaw chuck using an indicator

running on the OD because it was easier, but it could have been done using

the ID as well.

There are 3 jaw lathe chucks that independent jaws, but they are pretty scarce. Did you meant to say you centered it in a 4 jaw chuck?





What would you folks have done? The sleeve just just under 2" long.

I probably would have chucked the piece on the Od in my 3 jaw chuck and then used an indicator to see how centered the ID was. If the ID was centered enough that I could bore it to the size needed with some stock being removed all over the ID, then I would go ahead and bore it.

And if it was not close enough, then I would change to my 4 jaw chuck and center it using the Id.

One thing you might consider is not tightening the chuck too hard as it will distort the shape of the piece. And if you do not clamp it very hard, then you will have to take light cuts.

Dan

On 2014-03-02, wrote:
On Tuesday, February 25, 2014 1:04:15 PM UTC-5, Cydrome Leader wrote:


I went ahead and centered the pipe in a 3 jaw chuck using an indicator

running on the OD because it was easier, but it could have been done using

the ID as well.

There are 3 jaw lathe chucks that independent jaws, but they are
pretty scarce. Did you meant to say you centered it in a 4 jaw chuck?

There are three-jaw chucks with the same feature under various
maker's names, such as "adjust-tru" which offsets the chuck to tune out
the errors in the jaws at a given size. He may have one of those.

Or -- lacking one, *and* lacking a 4-jaw -- there is still a way
to do it. Measure the runout and find the highest point under a jaw.
Loosen the chuck, and put some shim stock (thickness equal to the
difference between the high point and the average) between the jaw and
the workpiece and re-tighten. Check again, and see how far out the next
highest jaw is, and repeat the shimming. By the third repeat, it will
probably be close enough.

And -- if you are going to *bore* it, I would have centered on
the OD, so the resulting final result would have the closest to equal
thickness on all sides. However, if I were going to turn the OD which
means gripping from the inside with the jaw steps) I would center on the
ID.

What would you folks have done? The sleeve just just under 2" long.

I probably would have chucked the piece on the Od in my 3 jaw chuck
and then used an indicator to see how centered the ID was. If the ID
was centered enough that I could bore it to the size needed with some
stock being removed all over the ID, then I would go ahead and bore it.

And if it was not close enough, then I would change to my 4 jaw chuck
and center it using the Id.

How much difference in centering between ID and OD or typical
pipe? I would center using the surface I was not going to machine, to
make the concentricity of the OD and the ID as close as possible.

One thing you might consider is not tightening the chuck too hard as
it will distort the shape of the piece. And if you do not clamp it very
hard, then you will have to take light cuts.

4-jaw will produce less distortion than a 3-jaw. 6-jaw will
produce even less -- and be the best choice with thin-walled material.
(Or turn some stock at least 1" diameter larger than the pipe, and bore
it to close to fit the pipe -- marking the part which is against the #1
jaw. Then take it out and make a radial cut 180 degrees from the #1 jaw
mark, and replace it using that mark to get it as close to where it was
as you can get -- then slide in the pipe and tighten. This will reduce
the distoration and spread the force around the pipe as much as
possible.

Enjoy,
DoN.

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wrote:
On Tuesday, February 25, 2014 1:04:15 PM UTC-5, Cydrome Leader wrote:


I went ahead and centered the pipe in a 3 jaw chuck using an indicator

running on the OD because it was easier, but it could have been done using

the ID as well.

There are 3 jaw lathe chucks that independent jaws, but they are pretty scarce. Did you meant to say you centered it in a 4 jaw chuck?

I should have been clearer. It's a standard 3 jac chuck with a scroll, so
centering just meaning twisting the part until it's close and then tapping
it so the end closest to the tailstock is as concentric with the part in
the chuck. It seems to be a constrant trade-off though with stuff like
pipe.

What would you folks have done? The sleeve just just under 2" long.

I probably would have chucked the piece on the Od in my 3 jaw chuck and then used an indicator to see how centered the ID was. If the ID was centered enough that I could bore it to the size needed with some stock being removed all over the ID, then I would go ahead and bore it.

And if it was not close enough, then I would change to my 4 jaw chuck and center it using the Id.

One thing you might consider is not tightening the chuck too hard as it will distort the shape of the piece. And if you do not clamp it very hard, then you will have to take light cuts.

Never though about switching over to the 4-jaw, but this makes sense.

It sounds like from your steps, the OD is reference for the rest of the
cuts. Is this a safe statement? It's easier to measure for sure.

On Sunday, March 2, 2014 2:30:16 PM UTC-5, Cydrome Leader wrote:


It sounds like from your steps, the OD is reference for the rest of the

cuts. Is this a safe statement? It's easier to measure for sure.

When you have something like this or a casting, you have to decide where to start. But where you start does not have to be the reference for the rest.. Once you have chucked on the OD and bored the ID, you probably want to consider the ID as the reference. And chuck on the ID and take enough of a cut on the OD to to smooth it up.

Dan