Question about belt reductions

[millman52]

I was wondering what width & pitch belts others are using & how much (3:1-4:1 etc.) on their initial reductions to operate a combination Ox fuel/plasma table. Will be using stepper motors.

[Torchhead]

For Rack and pinion with a DP of about an inch (3.14 inches of travel per rev) a 3:1 belt reduction puts you back even where one rev is close to 1" of travel. From your steppers you can expect from 500 to 800 RPM (once again depends on the stepper voltage applied) with higher RPM at about 20 to 25 times the stepper nameplate voltage. That equates to 500 to 800 IPM. In reality you probably don't want more than 400 to 500 IPM so even more aggressive reduction will trade the speed you don't need for the torque you do.

A lot of tables have been build with 3/8" wide XL belts of .080 or .20 pitch. You of course need to match the pulley pitch to the belts.

[massajamesb]

I know I have answered this one for you before, Neil, but I will answer on here for those who don't already know.

I have a 15 tooth pulley on my stepper, and a 40 tooth on the spur gear shaft, with .2 xl pitch pulleys and belts available here.
http://stores.ebay.com/HUBBARD-CNC-C...QQftidZ2QQtZkm
There are of course other places to get these, but I have always had good luck with Brent, who owns that store.

With my pulleys (15-motor, 40- drive) I have a 1:2.66 ratio, meaning that my motor must turn 2.66 (40/15) full revolutions to make one full revolution of the driven gear.
My driven gear is a spur gear, 20 pitch, 20 degree pressure angle, 20 tooth. For every revolution of the spur gear, my machine moves 3.14 inches (this will vary, depending on which spur gear you have being driven)
so, 3.14"/2.66 is 1.18" of travel for every revolution of the motor.

With this as just an example, figure out what the maximum speed you will need on your machine, and do the math backwards to help you find your desired gear reduction. There are a number of other factors involved in choosing your gear reduction and stepper motor, but this will help get you in the ballpark.

I hope this doesn't confuse all the newbies, and I hope I got it all straight without leaving anything out.