Tuesday, December 7, 2010

More on (Stepper) Motors

So, I will fully admit. I know next to nothing about machining. I know even less about gears, collets, shafts. The only bearings I've ever used were on a skateboard. Most of the reading I do on CNC-ZONE could be summarized as one big "that's what she said". I'm working on it, so bear with me.

"Hey, lets build a CNC"
"Ok cool, let's get some motors on ebay"
"This auction is for a new Applied Motion Products NEMA 17 sized precision stepper motor, part number 4017-871. This double-ended stepper motor has a 303 stainless steel shaft with a 19 tooth, 120 pitch, 20° pressure angle, pinion machined into one end of the shaft. The other end of the precision 5.000 mm diameter shaft extends 11 mm (0.433 inch) beyond the motor housing."
photo by Kristian D.

Lets work through that step by step shall we?

"NEMA 17" - Describes a standard for the size of the mount for the motor. Mounting holes for the motor are 1.7" apart, looks like this.

"double-ended stepper motor" - the axle sticks out the back.
"303 stainless steel shaft" - 303 is a grade of stainless steel.
"19 tooth, 120 pitch, 20° pressure angle, pinion" - A pinion is a small round gear. The pitch and pressure angle of a gear are a bit more complex:

I asked an architect friend about this and he said:
- P=N/PD for diametric pitch.
- circular pitch = 3.1416 / diametral pitch

I couldn't get the math to work that well but I'm sure I'm doing something wrong. Not sure what though :). The key things to know is that the pitch and pressure angle must match for any gears which work together.

"machined into one end of the shaft" - Thats what she said.



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