Total Nebie Question #2

[redbaron]

Hey guys, one more.

I have hand tapped many threads in my day, and was wondering how this is automated. How does a CNC machine tap or create threads in the stock. Is it a slow hi-torque process and do you need a special attachment (chuck) to do this.

As you can tell I am new at this but really excited about the possibilities.

[Rekd]

There's several ways. Most common I guess would be using a self-reversing tapping attachment, no special machine requirements. Or you could rigid tap it.. using a machine designed to do that; it syncs the spindle motion with the spindle rotation, and is very accurate. Or you could thread mill it.. using an endmill type cutter that has notches in it at the correct pitch.. then you program circles with Z moves to create the threads.

'Rekd

[castguy2003]

Well there are several options. If your control will do helical interpolation you can do what is called "Thread Milling" where a special cutter is driven in a 360 degree arc in X & Y (the thread diameter) while moving down in Z (the thread pitch) The nice thing about this method is you can mill just about any size or pitch thread, inside or outside.

Some controls also have "canned" thread cycles where the tap is heald in a special chuck and the control sends it down to a certain depth then automatically reverses. The tap holder usaually has some "float" in Z to take up for the difference in reversal time from the axis drive and spindle drive.

Do not try to machine tap with standard taps. Machine taps are designed to either pull the chips out (blind hole) or drive the chip down (through hole)


Mike

[Rekd]

Do not try to machine tap with standard taps. Machine taps are designed to either pull the chips out (blind hole) or drive the chip down (through hole)

Chips? You got chips?

'Rekd teh form taps unless otherwise specified

[HuFlungDung]

Ya Rekd, I bet you've got an EDM to take them out with, too?

[Rekd]

Originally posted by HuFlungDung Ya Rekd, I bet you've got an EDM to take them out with, too?

They have better threads, stronger threads, the taps are stronger. They work in most steel, alum, many plastics. And NO CHIPS.

In the last 3-4 years I've been using form taps almost exclusively. (Unless I'm doing Remec parts, which they specify cut threads) I haven't broken one yet. No, really. Not even one!

Err, wait, I did break one; used a cutting tap's drill instead of the form tap's.

'Rekd teh Convinced

[redbaron]

Cool. SO the "thread milling" technique uses a special endmill with a small cutter that creates the thread based on the z-axis depth speed and the x-y circular cutting rate.

THanks mucho guys! You're answers are really helping me understand the design in my head CAN be achieved.

[redbaron]

ALso will a desktop CNC machine (Taig, sherline, MaxNC) have the capability to do "thread milling"?

Thanks

[HuFlungDung]

There are multiple ways of doing this, Red. If your machine can do helical interpolation, then there would be no problem.

However, a lot of CADCAM software also has a utility to create helices composed of very short line segments which approximate the helix. In this case, you only need to check if your controller is capable of doing a 3 axis linear movement.