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There are several manufacturers of these testers. Vibrac in Amherst NH is probably the best known. They have lab or production systems that can measure motors with a wide range of inertia matching. (expensive but good) Magtrol has equipment that can do the job. Also, a company in the Chicago...

There are a few sites on the web that deal in used and surplus motors. Be aware of the output config. of the motor (gears, shaft features) to save a headache. Thomson is now owned by Danaher Controls, it that helps.

Brush AC motors are designed to operate in one direction. The commutator is shifted for optimum performance. If it is brushless and electronically commutated, then reversing is accomplished through the drive circuit.

You are looking at a very large motor. This type of setup develops moderate voltage with little current in a stock form.

Check with Lin Engineering in Calif. He makes small angle steppers and can help with details of inertia.

Some of the disc drive houses require balancing. There is a specific machine that does this, can't recall the name, but it's German and very tempermental

I think it is more common to freeze the shaft. This will allow a tighter interference when the temperatures normalize.

Thanks for all the suggestions. I am using a fairly standard NMB 608 with double shield. I will have an axial load of 200 lbs and a radial load of about 50 lbs. ressed on a shaft with an interference of a couple of tenths. We're using a tolerance ring to help center the bearing in a loose nest.

I've checked with NMB and NTN. I'll follow-up with the ones you mentioned. Thanks

Is there a simple rule of thumb for determining preload. I have checked the mfr's pages and they just say heavy enough to do the job and light enough not to cause excess heating.

In some cases, the cogging is due to an imbalance in the magnetic fields. This is especially true on canstack type steppers where the stator and rotor poles are equal numbered. I agree with the suggestion of increasing the pole tips, but this will detract from positional control if this is...