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Posted by David Littlewood on February 1, 2008, 10:06 am
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>
>Guys,
>
>Regarding the collet runout problems I've been having:
>
>I decided (as suggested) to re-machine the cone on the chuck myself.
>After carefully cleaning everything, and setting up the topslide angle
>even more carefully, I took a couple of cuts with a carbide internal
>boring tool, followed by a polish with some emery cloth and brasso.
>
>After re-checking runout, I'm now getting less than 0.0001" in the cone
>(which is about the same amount as the lathe nose), and less than
>0.001"
>with a test bar fitted into a collet.
>
>I said previously that I'd be happy with 0.001", so I gues my problem
>is effectively solved.
>
>If as above, I am getting virtually zero runout within the cone, but a
>bit more with a collet fitted, I guess this means that the collets
>and/or test bar are not quite spot on?
>
Garth,
How good is your test bar? When I tested my collet chuck, I used an
Arrand 2MT test bar, certified within 0.0001" for roundness and
concentricity (putting the 5/8" parallel part in the collet, obviously).
If you use something of similar accuracy, then it suggests your collets
are, as you say, not spot on. Probably not a lot you can do about this.
If, OTOH, you used a piece of BDMS or something of similar (lack of)
provenance, then it could be either. You might learn more if you take a
light finishing cut along the MS test bar, then turn it by 180 degrees.
If the collet is good, the turning should remove the eccentricity of the
test bar, and rotating it will not show any difference. If the collet is
out (either on parallelism or concentricity) then rotating the test bar
in the collet should show an *increase* in the runout.
David
--
David Littlewood
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>Guys,
>
>Regarding the collet runout problems I've been having:
>
>I decided (as suggested) to re-machine the cone on the chuck myself.
>After carefully cleaning everything, and setting up the topslide angle
>even more carefully, I took a couple of cuts with a carbide internal
>boring tool, followed by a polish with some emery cloth and brasso.
>
>After re-checking runout, I'm now getting less than 0.0001" in the cone
>(which is about the same amount as the lathe nose), and less than
>0.001"
>with a test bar fitted into a collet.
>
>I said previously that I'd be happy with 0.001", so I gues my problem
>is effectively solved.
>
>If as above, I am getting virtually zero runout within the cone, but a
>bit more with a collet fitted, I guess this means that the collets
>and/or test bar are not quite spot on?
>