A Modded Mantis: The BeeCNC

I took a look at the great work David Carr has done with his Mantis CNC mill for PCB fabrication. I love the simplicity of his design. I decided to build my own CNC mill, in the spirit of the Mantis but with a few modifications. My mill had some extra requirements:

• Build area suitable for 6.125” x 4.5” PCB from Radioshack
• Use salvage stepper motors from discarded printers
• Use ground rods from discarded printers
• Hold a Dremel tool as the primary spindle

I started my design at the build platform, a 5” x 7” layer of half-inch plywood. The tooltip needs to reach every edge of the platform, so the travel should be twice the length and twice the width in those respective dimensions. So, the interior bounding box is 10” by 14”, and the whole thing is a bit taller than the Mantis to accommodate the Dremel.

I don’t have the oft-used Arduino Mega for the brains of the machine, so I did some searching for suitable GCode-parsing firmware that would fit on a Duemilanove (with ATmega328P, 32K of program flash). I hope to use ReplicatorG with Skeinforge as the go-between for machine and design.

I found a great project called Teacup, an optimized rewrite of the FiveD firmware used with RepRaps. The firmware fits on the mega328, interprets GCode in real time, and has all the settings I need. I believe it’s made for 3D printers, but it should work fine for milling, a simpler operation.

I ordered three Sparkfun EasyDriver chips for controlling the stepper motors. The motors in question are NEMA 17 steppers, EM-257, from Epson, 1.8 degrees per step (200 step per rev). They seem to be manufactured by Astrosyn, and I found a datasheet. They’re fairly powerful little motors, but are a little bit difficult to mount.

For the power supply I’m repurposing an old HP server power supply brick. The whole machine should make quite a buzzing racket, and for that reason I decided I would call the machine the BeeCNC (in the spirit of insects like the Mantis, but a bit noisier). I’ll post some pictures soon.

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