The RotoZip bit was insufficient: too slow and it burns the wood, too fast and it breaks. I’ve ordered some endmills from Enco, which I’m much more optimisitc about.
The gear below was cut out of 1/4″ plywood, with and endmill too shallow to do the MDF. The partial gear in the background is made of 3/4″ MDF; the RotoZip broke just before completion, despite taking passes only 1 mm deep.
A bit charred
If you cut MDF too slowly, it will burn. Patrick recommends a speed of between 50 and 80 inches per minute, depending on the quality of the lead screw. The chapter on milling, in my upcoming book on Personal Fabrication for Make, will include a chart of suitable spindle and travel speeds for different materials.
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