Tap for myford spindle

I bought a Bison backplate and 6 jaw chuck for my Myford lathe.
The Bison back plate has burrs on it and and will not thread
onto my spindle. I even tried a second one and it has the
same problem.
Interesting fact is that the backplate will thread onto the spindle
if I start the chuck side. So I could screw it onto the spindle
and clean up the threads. I have done this before but it is such
a pain and the consequence or a mistake is screwing up a 100 dollar
backplate. Any chance of finding (or borrowing) a tap to clean up
the threads. Another question: Will the tap produce a thread good
enough for mounting a precision chuck?
Reply to
Charles A. Sherwood
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How precise can it be if it has burrs so bad that it can't be threaded on in the correct orientation?? I'd send it back, get a refund for defective goods (since you've already tried a replacement, with the same bad quality) and go looking for a good one - from some other manufacterer.
Reply to
Have you precisely measured the thread diameter of your spindle nose? For example, my 9" South Bend has a 1½-8 spindle nose thread, but it actually measures 1.503" which has brought me to grief a couple of times buying premade backplates. Even if I went out and bought a $50 1½-8 tap it wouldn't help.
If it is clearly burring then you can see what you can do with a jeweler's file. With the correct riffling file you can do yourself a lot of good sometimes.
Charles A. Sherwood wrote:
Reply to
Grant Erwin
The Nov-Dec 2002 issue of Home Shop Machinist has an article by a fellow that had the same problem with a collet chuck. He solved it by making a thread lap of mild steel. The lap was just an exact replica of his spindle nose. He charged it with 180 grit valve grinding compound from the auto parts store and screwed it in until it hit the interference, backed it up a couple of turns and screwed it back down about 20 or 30 times. He then removed the lap, cleaned the chuck threads thoroughly, and tried it on his lathe. It went on farther than before. He repeated the cycle three more times and was rewarded with a perfect fit and less than .001" runout.
Reply to
Randal O'Brian
Sounds pretty easy. I could even make a one time use tap by starting with drill rod and cutting some flutes. Seems like its worth a try.
Reply to
Charles A. Sherwood
I also true up a back plate anyway by taking a light cut before mounting the chuck. Fixing this back plate is a lot less work than making one. chuck
Reply to
Charles A. Sherwood
It isn't the threads that determine the precision of the chuck mount - it's the spindle shoulder that the backing plate tightens against and the last, short, piece of spindle that isn't threaded. The threads are just there to tighten it.
Reply to
Bob Engelhardt
Guy Lautard sells such a tap. He wants $96 for them, +$6 shipping.
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Bolo -- Josef T. Burger
Reply to
Josef Burger

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