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Trueing a 4jaw chuck
Steve sold me a nice little 4jaw chuck. Apart from chuck key (missing, and one screw's square hole undersized), it is all good. On the Hercus it went for immediate use, for turning down some 1m long stainless rods.
Then I noticed that this long stock was whipping around. Thought it was bent (which was why I mounted the 4jaw, to try and correct that), but eventually realised the chuck isn't parallel/perpendicular. Or rather, its back plate:
IMG_3883.jpg
2/10mm? Nearly 9 thou? That is significant.
Spinning it up also showed wobble on the outside.
It seems to be gyrating around the back (flat stepped register? of the spindle).
Now, most people wound just turn the back plate over –
threading the large thread against the spindle using a spacer –
and re-machine the small flange that locates against the spindle.
(Heck, I have done that before)
... but this back plate has a poor thread.
The side closest to the chuck is a bit tight and imperfect.
I don't want to spend time trying to repair the thread
(or try to visit Peter to use his 1.5" 8tpi taps),
so onto the surface grinder I go...
IMG_3885.jpg
1 thou:IMG_3886.jpg 2 thou:IMG_3887.jpg
3 thou, then test:IMG_3889.jpg IMG_3890.jpg
1 thou TRO? Not bad.
Almost perpendicular, and the wobble on the outside is almost gone.
Time to make some cast iron dust, and true the face:
2 thou:IMG_3891.jpg 3 thou:IMG_3892.jpg
I left it at that. Flat enough for the chuck.
Note the un-machined dip:
IMG_3893.jpg
Seems a bit odd, as there were initially turning marks all over the face.
Only thing I can think of is that it has warped?
Anyway, do a final grind of the spindle mating flange, and re-test:
IMG_3894.jpg IMG_3895.jpg
Very close.
I have ground one side, then used that with the thread to machine the other side,
then used that as a reference to grind the first side again.
Could probably go back and forth a few more times – successive approximation –
but this should be good enough.
Now, to bolt it all back together. The 3/8" bolts don't line up perfectly with the holes.
I enlarge them a smidgeon with a 25/64":
IMG_3896.jpg
and that fixes two of them, but the others are still misaligned:
IMG_3897.jpg
but the others needed more work.
Tried 13/32", which gave enough clearance on number 3,
but number 4 was nearly 1mm out. Too much to file.
10mm milling cutter:
IMG_3898.jpg
Last step, shorten the bolts a little, because they nearly foul on the pulley tensioner:
IMG_3899.jpg IMG_3901.jpg
And torque them up to minimise the run out:
IMG_3902.jpg IMG_3903.jpg
Attached Images
Read the full thread at metalworkforums.com...
