Feeds-n-Speeds

After stumbling onto this article by Niko Plath I started to look into speeds and feeds again. Every time I look into this I get confused. There is a lot of talk about it, but the numbers never seem to have much meaning.

Anyway I took the formulas from there article and made a google spreadsheet that lets you play with the numbers. The first set of numbers (vc, fz, d, z) are the normal inputs for speeds and feeds (in metric), those all derive from the cutter and its capacity to cut material (its base hardness and geometry).

In addition you can add limits on the spindle rpm and the speed of cut (minRPM, maxRPM, maxFeed). If these limits are applied then in the output I mark the affected columns in red.

Finally there is an English to Metric converter at the bottom so you can easily deal with english feed and speed numbers if you find them online.

It is interesting to put in various parameters and see the results. What you quickly realize is that for the limits of this machine you really always end up limited by the max spindle rpm. And if that was not the limit then you would quickly run into the max cutting speed limit. Basically in almost all cases you wan to set the spindle speed to the max.

In addition, playing with the tool diameter and number of teeth it quickly becomes clear that 3mm diameter tools with a single flute are the best choice. We could go up a bit on the diameter, and possibly support two teeth, but going any higher puts it well past the capacity of the machine.

I need to dig into this some more to see what else we can work out about feeds and speeds.

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