Stepper motors can run very quietly. They need not make any more noise when attached to the scope as when held in your hand. It's common star party etiquette to run a quiet operation, and you will make a good impression of your system.
The noise of the switching stepper motor windings is greatly amplified when attached to metal and wood mounts. The mount acts as a drum.
To run them quietly, isolate the stepper from wood and other resonant materials by a thin piece of rubber or styrofoam or something similar such as a mouse pad (neoprene). Use nylon screws or nylon bolts to attach the stepper to its mounting plate, further isolating the screws with rubber grommets. Use a short piece of automobile vacuum hose to attach the stepper to the input drive shaft of the gear reducer, leaving a gap of a millimeter between the shafts.
Another suggestion that receives rave reviews is to mount the motor with rubber standoffs, such as available from SmallParts.
Paul Shankland suggests using a PC wrist support made of a long strip of gel material. He goes on to say, "Cut away the hard rubber base revealing the material (color of vanilla pudding) underneath, with the cloth left on top - it's a tacky but cohesive firm gel, - looks like some syntheic blubber, and leaves a faint tacky resiude - very resiliant, absorbent, but of a resilience that with clamps, would not let the torque whip the steppers out of alignment. I think PERFECT for the job. I left the scope drive in my stateroom on the ship, so I took it in to toy with the damping qualities between bzillion meetings today and PRESTO- amazing quieting! BEST I have EVER heard!! Or not heard. The motors, about 95% haphazardly wrapped in the stuff, were sitting on a steel bench which amplifies noise heinously - but when I powered up the microstepping AND slewing, I thought the steppers were broken - I could not hear a thing!"
Here's a suggestion from Jean-Charles Vachon:
"I use a motor with a 2.25 inch square flange and I built aroud it walls leaving about 3/8 to 1/2 of an inch of space to put the wool.
"A word about the wool. Ascoustic wool and insulation
wool are not the same.Insulation wool has poor acoustic
properties. Insulation wool is a low density wool in contrast to
acoustic wool which is a high density wool.
"I would have to look for characteristics for acoustic wool. I do not remember by heart. It has been a long time I did not work with that. 7 years of retirement start to show. What I remember is that it is rated in pounds per square yard I believe. For instance in acoustic treatment we normaly use 3, 3.5 and 4 pounds per square yard. The heavyer the better is the product for acoustic treatment.If I am not mistaking acoustic tiles are around 3 pounds per yard which makes them excellent performer.
"A good way to see if the wool is firm enough is that it must stand up alone. The ceiling tiles are rigid enough for that.
Now if you put this around the motor particularly the square flange the motor does not move. I am just returning from the basement to check that particular aspect, nothing moves.
"I also drive the motors with a gizmo called Wellnut. This is a rubber thing with 10/32" threads at one end and a rubber hole at the other. It has 3/4" in length.They are of all sizes. The one I use can accept, in its hole, the 1/4" shaft from the motor dirrectly.The rubber is not hard and it makes an excellent universal joint that will accept and compensate for small misalingment between motor and worm.
"This is found at your hardware store and here cost 84 cents
only. This is the best thing we found to couple the motors to the
worm, thanks to Allan who made the discovery. I intend to use
them as well for my optical encoders.
"With acoustic wool well in place the motors should not move.
"To give you and idea of the results I got here with that : the noise from the fan of my computer is louder than the motor I have treated with the wool.
A suggestion from Tom Krajci on
reducing stepper motor noise:
"I've applied poster putty around my alt and az stepper motor bodies, and found that it's cut the motor noise by more than half. Poster putty is an adhesive putty that is used to hang lightweight objects on the wall without damaging wall paper, etc. It's sticky enough to stay in place, but the best advantage is that it's moldable to just about any shape, so I can get it into tight corners."
Although generally a very difficult item to find, Joe Zeglinski suggests looking into small scale device, "vibration isolation mounts and materials", used specifically to shock mount and vibration isolate PC hard drives and axial fans in noisy metal cases. Elastomeric motor mounts should help in significantly reducing stepper motor noise. He suggests one example might be products such as those produced by EAR at http://www.earsc.com