Re: Spindle register issue

m. allan noah
 

I have repeatedly done this experiment on a couple different lathes,
and the work always repeats to within a tenth, even in cases where the
register bore the the chuck backplate is several thou oversize. The
only time i see any variation is if I tighten the chuck differently,
and that seems to be corrected by the first good depth cut. Thats why
I feel confident enough to suggest heresy :)

If I were dead-set on enlarging the register, i would probably turn it
further undersize, and shrink a ring onto it, and then turn the ring
in situ. I'd try to avoid heating the spindle, don't want to mess with
any heat treatment, or cause any warping.

allan

On Thu, Jun 21, 2018 at 8:28 PM, Davis Johnson <davis@...> wrote:
HTRL agrees with you (heresy around here, tho).

I'd be interested in an experiment.

Chuck up a short piece of scrap, turn the outside for a bit.

The part you just turned will be exactly concentric. Check it with an
indicator.

Unmount/remount the chuck several times without removing the piece of scrap.
Each time check it with an indicator.

I really would be interested in the results, and would do the experiment
myself except that I don't have a chuck with a loose register.



On 06/21/2018 08:15 PM, m. allan noah wrote:

I'll buck the conventional wisdom, and state that the register
diameter does not matter at all. The conical face of the thread, and
the flat shoulder behind the register are sufficiently to achieve
kinematic positioning of the chuck.

I daresay the problem is your testing method. Reground jaws is
basically meaningless, unless they were ground on the lathe in
question, properly preloaded, with the diameter set to exactly the
size of the stock you are now holding. Take of the chuck, and put it
back on, and see if it is consistent. That is a true test.

allan

On Thu, Jun 21, 2018 at 8:00 PM, carbure2003 <guycad@...> wrote:

About. a year ago, I bought a 10K spindle on ebay.

As I have not used much the lathe where I fitted the spindle, ( only with
collets) I never noticed that the register was under sized. (1.495 in dia),
quite likely machined by a previous owner.

I trialed a chuck with freshly re ground jaws on it and it was defenitely
off centered by many thou.

Register defenitely has importance when yo want to swap chucks from lathe
to lathe and keep chuck accuracy.
Did somebody ever attempt to rebuild a spindle register ? (Register is
1.510 in dia on my other SB)

If yes, how did you proceed? (Welding is not an option)

Thanks

Guy Cadrin
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