Combine two of those mounts with one of those couplers, add two NEMA 17 steppers (the one on the right is that one), slide a baseplate underneath, sprinkle with various screws, and shazam you get a stepper motor dynamometer:

Stepper Dynamometer

The baseplate puts the mounts 65 mm apart on the 10-32 screw centers, which is entirely a function of the coupler length, and is easy with manual CNC on the Sherline.

Changing the motors is straightforward: loosen coupler setscrew, remove base screws, slide motor away from coupler, remove mount screws. Won’t happen that often, methinks.

The general idea is to drive one stepper with a known current, apply a known resistive load to the other motor’s windings, and then plot torque vs. speed. It won’t be quite that simple, of course, but should produce some interesting data.

This simple cylinder connects two NEMA 17 stepper motors together:

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.