How much work would be converting Prusa firmware/software for CNC use?
That is the way to overcome the worst problem of converting Prusa to CNC: the flimsy mechanics not able to withstand stress and vibrations of machining. Then I can connect the drivers to the 3 axis of Prusa's electronics, optionally connect some driver of the spindle to the extruder output (or just control it manually), and it seems the hardware side of the device is done.
The problem is the rest - adapting the software. RepRap family of 3D printers being open source means their software and hardware can be adapted. It's only a matter of how hard it is.
Does anyone have any experience in that direction? What would such conversion involve? Just recalibration to the new gear/leadscrew ratios, or something more involved, like editing the sources to get rid of all the temperature safeguards and the likes?
RE: How much work would be converting Prusa firmware/software for CNC use?
I wouldn't recommend it. CNC milling is a dirty/dusty thing. 3D printers are not designed for that and you need to rebuild almost everything. Just pick any CNC open source projects and go from there. Converting 3D printer to CNC machine and especially any Prusa printer doesn't make sense either money or technical wise.
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RE: How much work would be converting Prusa firmware/software for CNC use?
Start with Marlin code, not Prusa code, and you'll be ahead of the curve.