DIYbanter - View Single Post - Lathe with threaded spindle

Terry Coombs

wrote:
On Jan 3, 7:59 am, "Terry Coombs" wrote:
DoN. Nichols wrote:
On 2009-01-02, Jim Stewart wrote:
I just finished a cast iron adapter plate that
mounts a plain-back 5C collet chuck to the 2"-8
tpi spindle of my lathe. I can easily dial in
the mounted chuck to .0005" runout, the limit
of my measuring capability.

When I remove and reinstall the chuck/adapter
plate assembly and check the runout, it varies
from .0005" to .004". It only takes a couple
of minutes to mount the indicator, loosen the
bolts and recenter the chuck, but I was hoping
for a little more repeatability.

Am I asking for too much here?

For a threaded spindle -- yes I think so.

Good Luck,
DoN.

I'm not so sure Don ... If he machined the recess on the back of the
plate so it seats on the register face , it should be pretty close .
I can remove and reseat my 4 jaw with a piece of stock dialed in and
have it close enough that my dial indicator can't mearure the
difference. --
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I've machine more 1"-10 and 1 1/2"-8 backing plates over the years
than I care to remember...

Here's how I did it, and the results were acceptable at that time.
Forgot whether it was .0005" or .0007" repeatability, but it always
was less than .001", even on the little Atlas 6" lathe I had for 25
years.

1) Chuck the new 7 unmachined plate and turn the front face (outboard
face) flat.

2) Bolt to face or sturdy driving plate. I prefer this because the
work may shift in a light chuck when cleaning/boring a cored hole.

3) Face boss and bore hole to tap drill size.

4) Bore locating bore to depth, and with dia. equal to the locating
dia. on the spindle, + .0003" to + .0006" or so. Personally I keep
this a close as possible to less than .0005", but it depends on your
skill as machinist and ability to measure accurately. Turn a 1/32"
chamfer on the outside edge of the locating bore.

5) Now machine the thread to match the spindle. I made an acceptance
thread gauge to verify the fit-up to the spindle without trying it,
but you can unscrew the assembly and try it. If necessary it is
easily returned for re-machining to open up the thread. I found the
thread gauge a great time saver. As mentioned earlier the thread
should be an easy fit on the spindle.

6) Because the threading operation will leave a marking of some depth
in the locating bore, deburr this using emery cloth.

7) Clean the bore with a tooth brush and oil lightly, and you are
good to go.

8) After removal and prior to re-installation always inspect the
threads on spindle and bore, and clean thoroughly, oiling lightly.

The reason for this order of machining is that if the locating bore is
finish machined after the threading operation the interrupted cut
would, in all likelihood, result in a bore not concentric to the
thread.

Another thing, I found commercially finished threaded backing plates
have these locating dia. machined waaay oversized.

The method as described above has given predictable results.

Wolfgang

I was taught that the chuck will center on the thread , and square on the
register face . The actual mechanics aren't that important to me , as long
as it works . I recently cast and machined an adapter plate with a
"spindle" to mount my chucks on a rotary table . As long as I can center my
work on the table , I'll be happy . Haven't had a chance yet to mount the
table and check runout , the wife's had me runnin' like a rabbit this
holiday season .
--
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