stiffness measurements cnc mk3

[Jonathan]

I get a feedrate of 900mm/min. I'll keep experimenting with the next parts I cut out to see if I can get a better finish.

600mm/min @ 12000rpm generally works well with a single flute cutter, so since one would expect the chipload to be slightly lower for a 2 flute cutter, as a first approximation the feedrate should be a little less than 1200mm/min.

What are you mounting the workpiece on? It can make a big difference to the finish - for example I found it easier to get a good finish when taking a small cut with my machine when it had the MDF bed. Presumably the MDF's damping properties helped. If the parts are small you'll obviously have problems with rigidity using MDF, but if they're a reasonable size and you add a finishing pass (take off 0.1-0.2mm from edge in one pass) you can get good results, e.g:


(20mm thick parts and 25mm thick bed)

I've still not measured, but I'm pretty sure your machine is stronger than my 'old' one which cut the parts above (and below), so unless you have big problems with resonance you should be able to get similar results. Perhaps MDF is worth a shot? That's not to say you can't get a good finished clamping rigidly to aluminium, it just takes a bit more care/luck setting the feedrates, e.g: