The pump had been tripping the breaker on and off for months, but you know how there is never enough time for maintenance until it's too late. The new hire is a retired Marine who has some toolmaking experience, and showed up early and ready to work. Unfortunately, he was scheduled to run the HAAS, making parts for our sister shop. We got him going on a simple mill job, deburring and polishing once the parts had run.
The optics part has a .800 bore thru, a rectangular profile, .9-40 id threads, and 1.062-40 od threads on the boss.
Of course, coming from a mill background, and already having it set up in a vise, I decided to go with a threadmill. There was also the matter of having a lathe down, and an eager customer paying an expedite fee.
The one I used had a 1/4" shank and a 3/8 cutting diameter. While it has five flutes, it cuts only one thread at a time. I like the threadmills that have the form of the thread ground into the tool, but I can use this style for any pitch, and regrind it when it dulls. This one had already been ground nearly to the end of it's usefulness.
While I used FeatureCAM to generate my program, the code for threadmilling is surprisingly simple.
For OD climb milling where XY zero is center of part:
G00 X-1. Y-.2
Z.1
G01 Z.025 F10. (ONE PITCH ABOVE PART )
G41 D33 X-.875 Y0.(X = MINOR DIA OF THREAD + RADIUS OF CUTTER)
G91 (RELATIVE MOTION)
G02 I.875 Z-.025 L8 (L IS NUMBER OF REPETITIONS)
(IF MACHINE DOES NOT RECOGNIZE L, COPY AND PASTE G02 LINE 7 TIMES)
G02 I .875 (OPTIONAL, WILL MAKE GROOVE AT BASE OF THREAD)
G90G40 X-1.(ABSOLUTE MOTION, CANCEL OFFSET)
G0 Z.1
I needed a thread relief groove deeper that the threadmill could provide, so I did a simple interpolation with a dovetail cutter, between the rough and finish pass.
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