Stepper Motor Shaft Coupler

This simple cylinder connects two NEMA 17 stepper motors together:

Stepper Shaft Coupler

Stepper Shaft Coupler

It’s quick-and-dirty:

  • Cut 2+ inches of 0.375 drill rod, face both ends
  • Drill #8 = 0.199 inch = 5.06 mm (because #9 = 0.196 inch = 4.98 mm is a bit too snug)
  • Cross-drill #41 in the Sherline (because #43 makes for stiff tapping)
  • Tap 4-40 for the setscrews
  • File off rough edges, run #8 drill through the bore to clean out tapping chips &c

Now, you probably don’t want to do this in real life, because you want a coupler with a bit of compliance to soak up the inevitable misalignment and dampen the mechanical resonances.



  1. #1 by Brent on 2011-08-24 - 09:37

    Why would you wan to connect two steppers directly together? Or is that bit saved for the next installment?

    • #2 by José Romero (@cyborgar) on 2011-08-24 - 10:19

      Stepper motor wrestling!

    • #3 by Ed on 2011-08-24 - 17:56

      Why would you want to connect two steppers directly together?

      It’s a dynamometer: one will be a generator. Well, an alternator, but you get the idea: load the output, measure the power, divide by RPM, and get torque. I think it’s easier than a de Prony brake, but maybe less accurate.

      saved for the next installment?

      If I worked all this stuff out in advance, it’d look a lot like, uh, work.

      As it turns out, though, this will be part of a Circuit Cellar column, so you’re seeing the pieces as they happen… which is sort of the point of this whole bloggish thing.

  2. #4 by smellsofbikes on 2011-08-24 - 13:44

    I’d be interested in hearing your approximation of which drill to use for taps. I use the listed size for aluminum and one larger for steel.

    • #5 by Ed on 2011-08-24 - 18:01

      approximation of which drill to use for taps

      I use pretty much whatever the chart says for aluminum and plastic: roughly 75% threads. For steel, we think alike: one size larger gives lower tapping force and fewer broken taps. I don’t need the ultimate possible strength, so pretty much anything will suffice.

      There’s a table taped to my stainless steel screw box listing the tap and clearance drills… saves me a trip through the big chart for almost everything I make. For the 3D printer stuff, I’m slowly building a list of screw & nut sizes that should produce near-net holes; eventually I should turn it into an include file.

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