I’ve commented elsewhere about this too, it’s actually rather complicated to get the right feeds/speeds/plunge-rates/step-overs/waterline-pass depth etc… because they’re in an interconnected relationship. That said, there are a few constants you can work from:
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Recommended chip-loading for your given cutter in a given material. You can find chip-loading charts online in a number of places. Onsrud in particular has a few decent ones for their tools, and here’s one from [PDS spindles][1] that’s also pretty good.
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Maximum spindle speed and axis feed-rate your machine can offer. In our case with the Nomad it’s ~12krpm, but I would recommend keeping it under 10krpm, and 100ipm maximum travel speed on an axis. As I’ve posted elsewhere, it’s an inverse relationship between torque and speed, so the faster you go, the less force you can exert. If your spindle is being asked to spin too fast, it may not be able to exert enough force to work at the recommended chip-load for the cutter & material. If you have too high of a feed-rate you’re “crashing” the spindle into the material instead of letting it cut, so the steppers miss steps. This is most pronounced in dealing with turning corners and lateral entries into the material, and is the worst when you’re doing a full-diameter plough-cut with the tool. Taking a slightly less aggressive step-over can help a lot to reduce the lateral force on the spindle.
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Recommended depth-of-pass/maximum step-down for cutters is recommended to be 1x the diameter of the cutter if working at the recommended chip-loading, or you can decrease feed by 25% for 2x depth, or 50% for 3x depth. Because of the machine limitations, you’ll probably need to reduce feed/speed rates to make things work out at the right depths, but you’ll probably end up with less cutting-time overall and less wear on your tools as a result.
Until we can collectively get some values put together, those guidelines should help, plus the formulas which I’d put up for [3dSteve here][2].
Happy machining!
[1]: http://www.pdsspindles.com/engineering-speeds
[2]: First 3D Cut and Lessons Learned