Timing Belt speed reducers

One of my customers wanted to use one of my MCG ID23005 nema 23 servo motor on an axis that was not suited for a direct drive. I calculated that to use 80% of the output power of the motor that he would need a 5.4 to 1 reduction. This reduction would require use of a jack shaft between the motor and the output shaft.
He did not have the equipment to make a speed reducer so I offered to build it for him at a nominal price.
I designed a base plate and a motor plate that would fit his nema 23 mounting flange. Using a .1875 end mill I bored the base plate and the motor plate to fit .250 ID ball bearings. I also bored two other .625" OD holes for two more bearing to support the jack shaft.
In the design process I used the center distance calculator at stock drives Inc. When I received the parts and install the .080 pitch pulleys on their shafts and into the base and motor plate I found it quite difficult to insert the main drive shaft bearing into the base plate with the timing belt over the jack shaft pulley and the output shaft pulley but after several attempts finally got it assembled.
The question I have is the center distance calculator designed to give the belt a really tight fit over the pulleys? It sure seems like the belt is overly taunt but I double checked my drawing against their calculator dimensions and it right on. The base plate and motor plates are also right on. Other wise the speed reducer works as it should.

Dan Mauch
economical 3D scanner software and kits
low cost stepper and servo motors.
cases for Gecko drives
kits and assembled 3-4 axis drives
www.camtronics-cnc.com
www.seanet.com/~dmauch


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