Tuesday, December 7, 2010

CNC Electronics: Choices

Some random facts I've learnt about CNC electronics:

- there is math involved with deciding optimal voltage for motors, and subsequently deciding a large enough power supply and drivers. A lot of the "kits" on ebay are of badly matched components that would not work optimally.

The most important thing with a CNC build is apparently you need to understand this is an entire hobby in itself: the learning, building, maintaining of a CNC. It's not just purchasing a tool that will then output parts.

The upside is great though, a CNC would be an excellent start to many home fabrication business (tons of art options, hobbiest support, synth building, pedal building, etc, etc)

This website seems like a great resource for starters, walking through a lot of the terminology and choices involved in a CNC build. The rest of this post is a lot of summarized info stolen from that crevicereamer link. (what a name)


For PCB milling around 60-80 oz./inch NEMA 17 motors should be more than sufficient. Trying to find numbers for wood and thin aluminum.

"BIPOLAR PARALLEL" wired steppers are the best design for CNC as they maintain their torque at high speeds.

"Stepper motors need around 20 times their rated voltage to perform at their best."

"For the EXACT Max/Best power needed for a stepper motor the formula is 32 times the square root of motor inductance in mH. EXAMPLE: A motor with 4 mH inductance would need a 64 Volt PSU. The PSU must be sized for the lowest voltage motor--So a 64 Volt motor combined with an 85V motor would need a 64V PSU. You would then pick the PSU that is at or as closely below 65V."

"AMPERAGE: To determine the PSU amperage required the formula is 0.6 times total motor amps. EXAMPLE: Ampere rating for three 3 Amp motors would be (3+3+3) times .60 = 5.4 Amp PSU. Some apply a safety margin and use 0.67 as a factor instead. You only consider the Amps for ONE phase of a 2 phase motor. A motor rated at 3A per phase will count as 3A in the calculation--NOT 6A."

From Amazon, this looks like a decent deal: Zen Toolworks CNC Carving Machine



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