Re: Acer Vertical Mill w/ CNC retrofit Proper Feeds and Speeds for Plastic Cutting
With an end mill I would use a spiral ramp (about 1degree ramp) and cut the full 0.125'' depth in one step down if the hole diameter is critical. But I really think the proper tool for this job is a step drill. I have a similar machine, and have a similar job coming to do tomorrow where the holes are 0.875''. I'm going to use a step drill.
I'm not sure a down cut end mill is the correct tool for this job. I think a really sharp standard bit would be a better choice. 3/8'' bit is fine, as is the RPM,I tend to cut plastics at a bit slower SFM than most people to keep it from melting. But I might bump the feed speed to 20 IPM to increase the chip load. Like mine, your machine, or any knee mill, is not well suited for high feed speeds. If I were doing this in my Haas, I would be using about 150 IPM feed and bump up the spindle speed to maintain about a 0.004'' chip load. I would not use a 5/8 end mill, maybe a 1/4'', 2 flute.
If you can properly support the working surface on a spoil board it will help with the chatter.
Jim Dawson
Sandy, Oregon, USA