BMatthews

Max Power, since you already made ONE tap to this thread size why not simply make another. But this time make it from drill rod and then harden and temper it following all the shaping operations?

I've done a few of my own custom sizes in that way and it's not that big a deal.

With the picture in the first post you're on the right track but you need to make the gullets a LOT bigger. The cutting teeth will not be relieved on a home made tap similar to how they are on factory ground taps. So the key with a 17/32 diameter tap with fine threads of this sort is to cut away 5 or 6 gullets so you leave about a 3/32 to 1/8 wide set of threaded "lands" to do the cutting. Even then I like to lightly releive the peaks on the trailing edges.

To get a good start you'll also want to lightly chamfer the first couple of teeth with a file before you cut the gullets out.

OK, I just took the time to do a sketch. Shown here a 17/32 thread and using a 3/16 chainsaw sharpening file it looks like you'd get a good tapping form from using 5 gullets. Note the arrow showing that you don't want to simply plunge straight down. It'll cut much more effectively if the teeth have a slight hook angle which you can get by starting with a straight plunge and then push to the side as shown by the arrow to get the hook shape. Note that you need to sink the file in a little past half it's diameter to get this.

I didn't show it on the sketch but with 5 gullets the resulting cutting lands are .1 wide if you shape the gullets as shown without a lot of excess opening. That's about perfect for getting a good "follow" during the thread cutting but without creating too much drag.

You'll likely want to make TWO taps like this. One for a starter and one for bottoming if you will be running down to a flat stop like the Cox heads. So take careful notes of your numbers on the first tap so you can replicate it for the second.

For measuring the thread cut depth for things like this I'm a big fan of the "3 wire" method. This is where you use wires that fit down into the "V" of the threads so the wire sits on the walls of the "V". For 32TPI this means you want to use something like .018 wire. The idea is that the wire sticks up over the peaks so you can get a meaningful measurement of the pitch diameter that you can use for comparison when cutting the threads on the taps. Whatever you get on the glow head threads add .002 to ensure some play to be able to spin the heads in.