LOL . Huckshaw , I would have sold you 2 collett chucks plus the colletts for $50 + other related pieces . I have them still , but a learning experience is priceless in the making of a fixture . I have had many a failure also , but we as machinists call our mistakes ECNs . ( engineering change revisions or notices ) . Machinists can never screw up a G job , only improve on our prototypes !
So how much run out is too much in a collet chuck?
I chucked up a 1/2 end mill and gorlt .0015-.002 run out then tried a newer 1/2" end mill and got .001 @ about 1/2" from the chuck. And compounds as you get further out. Couldn't test too far on account of short end mills. So the first end mill either was bent or sat differently than the second. I do not have dowel pins to test better.
What do you think?
Thing about an ER collet is it needs to have more length into it to grip correctly.
You might need a longer test piece.
TIR of .0006 would be my choice for an ER collet chuck.
So some drill rod for a better test. I also noticed it very much depends on how about you get the nut too.
Maybe it would be worth taking another swing at the taper. Or maybe a cleanup pass over the thread.
I did use some sand paper inside the taper cause my compound isn't the smoothest it seems. It's ripe for a rebuild and some bearings.
Tool post grinder would be nice. Compound would still need to be smooth though.
Drill rod is not always straight either. You could mark it and release and turn and measure again to verify.
If the rod was straight the reading would never change.
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