There's nothing wrong with having "flat topped threads" (so long as the part which is mating with them is fully-formed), and I actually like to have the tops flat because it is far more comfortable to hold a pen. I typically make the tenon a smidge smaller than the nominal size of the threads I'm using: for 12mm x 0.75, I'd aim for a tenon diameter between 11.9mm and 11.95mm. Some materials that are soft (acrylic acetate, ebonite, celluloid) don't put up as much of a fight, but for the most part it's necessary to have some kind of ramp that the leading teeth of the die can slip over before they start to bite into the material. Mike, I believe not having a chamfer at the end of the tenon is the main factor causing trouble. I have also now ordered a brass rod-so I can give that a try!
However, the question is, what was wrong with the 12mm tenon size in aluminium for the die I was using?. I bought a 1 metre length of 15mm rod for £10 (English) so I still have a lot to play with without it costing a lot, and I am learning a lot in the process. The pen was not successful but I am still trying. However, I turned the tenon down to 12mm, but the die would not even attempt to make a thread, and in the end, I had to gradually turn the tenon down significantly to enable the thread to start. However, after recently seeing an article on the Web about making an aluminium pen with a slimline kit on a woodturner's lathe, written by Walter Hall in Woodturners magazine a few years ago, I decided to attempt a kitless pen in aluminium after making a decent attempt using a kit.
The 12mm tenon worked well on acrylic blanks, although being a novice at kitless pens, I am still waiting for a finished pen I can be proud of!! My die for the internal cap thread and the corresponding male thread is 12mm.
#Micro drill tap chart how to#
As a relative newcomer to kitless pens, I asked this question about how to calculate the size of the tenon for using a die in a recent forum, and I had an excellent response from Monophoto.
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