THREADMILL PROGRAMMING HELP SHEET FOR UN INTERNAL THREADS

When programming threadmills the start position in X and Y should be at the center of the drilled hole.  The Z start position will be at the top of the part.  All the programming is done in incremental mode since the absolute hole positions are not known.  All the cutting will be climb milling.

• When programming, the machine will go thru the following sequences:

• (0-1) Feed Z in at 30 IPM to the full thread depth plus 1/8 of the pitch

• (1-2) Feed X and Y to position 2 (clear dia) and activate the cutter comp.

• (2-3) Feed CCW thru 45 degrees at the programmed feedrate in X, Y and Z to ramp out to the major diameter. The Z move will be out of the part and equal to 1/8 of the pitch (45/360 degrees=1/8)

•  (3-4) Feed CCW around the entire circle to cut the threads in one revolution.  The Z move will be out of the part and be equal to the pitch (ex: 16 pitch = .0625")

•  (4-5) Feed CCW thru 45 degrees to ramp out of the part to the clear diameter.  The Z move will  be out of the part and equal 1/8 of the pitch.

•  (5-6) Move the cutter back to centerline at 30 IPM and delete the cutter comp.

 The last move is to rapid Z out to the top of the part and then go back to "absolute" mode.

This is a generic program that may not be suitable for all machines.  Verify that your machine is capable of helical interpolation.  The vast majority of CNC machines manufactured in the last ten years have the helical interpolation capability.  Machines manufactured before that time usually supplied it as an option which can be enabled with a parameter.  The best way to see if your machine is capable is to MDI the part program below into the machine and see if it will make the moves.

It is generally recommended to cut fine threads in one pass and coarse threads in two passes.  If you need to use two passes, just repeat the program below and use a different D word to reduce the depth of the first pass.  If you are cutting a 3/8-16 thread, increase the offset for the first D word by about 35% of the pitch or (.35 * .0625) = .0218

An EXCEL sheet which calculates all of these values is available at no charge to our customers.  Please e-mail Rick at rickk@threadmillsusa.com for a copy.