Mike,
Keep this in mind: You will NOT satisfy a thread gage form tapping in Delrin or any other plastic. You just have to accept the fact that the threads are going to be tight on the screw, which is, at least in my case, the goal. If you are doing this on a professional level, clear the end result with the customer first. I have brought this to the attention of a couple of my customers', and they have been fine with it, and subsequently very pleased with the results. But they appreciated the head's up to know what to expect. The "Nylock effect" doesn't occur in metals, that I have seen.
For the record, I form tap everything I can. Aluminum, Delrin, tool steel, stainless, whatever. It all works... Up to a certain size. I have a 3/8-16 form tap that I use in aluminum, but it's a bruiser on the hands. They are especially nice for blind holes. Start the tap on a machine (if you can), then drive it to the bottom by hand. No tap chips to try and clear out of the way while finishing the thread depth. Truthfully, you get a better result from form taps than cutting taps, as forming the material provides a work hardened surface in the threads, better finish and more consistent pitch sizes. Not to mention the fact that form taps are far less likely to break than cutting taps, due to the lack of clip flutes. Just know that if you DO happen to break one, you're not likely to get it out by whatever means you would normally use to get it out.
One material I can tell you that does NOT like to form tap is 440 stainless. I don't know what it is, but it doesn't work. I had to learn this lesson the hard way (thank GOD for thread inserts
) I also have not had the cajones to try form tapping titanium or BeCu. Otherwise, use a good tapping fluid and have at it.
Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine And Precision LLC
