Taper Turning Revisited

A while back I received some very good suggestions on RCM for turning tapers. I put them to the test and turned some tapers with one new wrinkle - the lathe tool was mounted upside down and fed from the compound on the back side of the workpiece. This method suggested by Sherline seemingly allows more control via better visibility.

Later I decided to make some WW square and hex collect blocks to use with the small Sherline vise. Having a set of WW collets from 1/64 through 5/16 ", the quick set-up collect blocks seemed like a good addition to my Sherline collet set. So I set out to make everything on my big lathe, using

5C collets for good centering. Turning the 20 degree collect nose tapers in the blocks was a piece of cake but then, Bam! Trouble reared its ugly head. I had no tap to thread the WW collect opening in the drawbar for collect closing. What to do? Careful measuring revealed the thread to be 9/32 -
  1. Human, that's a strange one. None were found in my tap drawer. OK, let's look in the catalogs and buy one - none listed in 3 or 4 catalogs, none shown in McMaster-Carr on line.

What to do now?? Quitting wasn't an option with several hours work already in the project, besides it would be really cool to have a pair of WW collect blocks. So, hey!, let's make a tap to thread the WW drawbar. Raw stock came in the form of a 5/16 drill rod turned down to 9/32. The drill rod, held in a 5C collect, was threaded 40 pitch on the big lathe and the end chamfered 3 threads. Then the new tap was heated to "beyond magnetic" and quenched in oil. While still warm from the quench it was tempered for 45 minutes in a 350 degree oven. (the wife wasn't home)

So now if I ever need one again (unlikely) I have a very special 9/32 - 40 tool steel tap for threading the male ends of WW collets.

Bob Swinney

Reply to
Robert Swinney
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Thanx for checking, Jim! After reading your reply, I went back and looked in the MSC catalog again . . . . yep. ! there they were, in the special tap section of the catalog. But hey! It was a good learning experience, anyway. At $18.46, MSC's is a bargain! Figuring my time at $100 per hour *my* tap worth about $300, not counting the Sherline threading attachment and 45 minutes of electricity to heat treat.

Reply to
Robert Swinney

According to Robert Swinney :

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To add to the fun -- that is not a normal thread form It is a buttress thread. Look at a collet under magnification to see what it looks like.

Here is an eBay auction selling them:


He also sells the taps for the 10mm (D size) collet drawbars as well. (Hmm ... he specifically says that the 10mm is a buttress thread, but does not for the WW collets, so I may be wrong.)

Enjoy, DoN.

Reply to
DoN. Nichols

Yeah, Don. Going in to this project, I would have guessed the littlle collets were buttresss threaded but upon close examination they proved to be ordinary 60 degree threads. I suppose in such small sizes there is not enough loss in strength, standard over buttress, to justify the extra complications of "square" threading. I would expect larger collet threads to be more square; however I think 5C's are 60 deg. (not that I'm going to try to make any).

Reply to
Robert Swinney

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