Adding the letter P to the end of any move command causes that move to start in sync with the spindle.
You can make a do-it-yourself threading cycle by programming each cutting pass to start in sync with the spindle. This gives you more control over the depth of cut on each pass and the pullout position.
Putting the letter P on the end of the command line for any move causes that move to start when the spindle reaches its zero position.
With this feature, you can put threads on an arc if desired. Special 'bone-screws' sometimes require threading on portions of an arc. Also, you can do multi-pass thread-milling.
Here's a thread-milling portion of a program for doing a 2-56 thread:
The thread mill head was .062 diameter, and it was set so that when the tool was on center the X dimension was .062. The mill is programmed it to take 3 passes just to illustrate how the P function works. Since the thread-milling cutter is spinning pretty fast, you probably don't want more than 200-300 rpm on the spindle. This example assumes a .067 drilled hole with a depth of cut of .01" on the initial pass, and a thread length of .25".
| T1 | x.062z.5 |
| z.2 | z start location |
| x.077 | (position to take .01" on 1st pass) |
| g04f.2 | (short delay gives a little settling time) |
| g95f.01785 | (feed 1/56" per rev) |
| z-.25p | (1st thd pass note P) |
| x.062 | (retract back to center) |
| g94f100z.2 | (retract Z) |
| x.083 | (take a little less on the second pass) |
| g04f.2 | (settle for a while) |
| g95f.01785 | (feed 1/56" per rev) |
| z-.25p | (2nd thd pass note P) |
| x.062 | ((retract back to center) |
| g94f100z.2 | (retract Z) |
| x.086 | (last cut takes even less) |
| g04f.2 | (short delay gives a little settling time) |
| g95f.01785 | (feed 1/56" per rev) |
| z-.25p | (last pass note P) |
| x.062 | (retract back to center) |
| g94f100z.2 | (retract Z) |