This is one of the trickier parts someone has asked me to make, and the trickiest I've said "I'll try!" to. It's a screw for a (I assume) plastic extrusion or injection process, made from 4140. .500" x 12" long makes for a not-at-all rigid setup, and it took a few experiments to figure out what would work. I started with a piece of 6061, just to test the code, which was written by hand as I haven't done enough 4th axis work to justify the cost of upgrading my CAM. The aluminum test piece went well, so I switched to the 4140 and the chatter pretty quickly got fatal, so I knew I would need some serious support.

In the end, I took a piece of aluminum and milled out a .500" diameter channel that would sit directly in line with the workpiece. That, plus a little judicious use of a manually-applied semi-rigid vibration damper (aka rubber mallet) kept things in the happy. I used a .375" Maritool 4-flute carbide EM with .015" radius, running around 1800RPM and 2.46IPM at full-width passes .02" deep. The speed was limited by the rotation speed of my rotary table, and DOC was limited by rigidity concerns. This was a 1-piece job, so once I had a formula that seemed to be working, I decided to stick with it. Machining time was about an hour, setup and figure-it-out time was a lot more than that. Customer was happy with the photos, so it's a good start, but the proof will be in the (plastic) pudding it hopefully makes.