V-belt stepped pulleys are commonly used in mechanical drives where a speed selection is desired. Here the concept is extended to synchronous belt drives providing speed selection with the many advantages of synchronous, i.e., toothed, belt.
A typical two-step pulley is pictured on the left and a typical BLDC spindle motor application is pictured on the right. Here the spindle pulley has a flange on the larger pulley, but the flange is not required.
Note that larger pulley has a tapered area, matching the flange taper, to guide the belt onto the pulley face. Pulley faces have a width standard for the selected belt width. A single long cup-face 10-32 set screw enters through the larger pulley face and binds both pulleys to the shaft.
A typical application will match a pair of step pulleys such that the center distance is maintained within the adjustment range for each step. A relatively short center distance is suggested to ensure that the belt remains centered on the pulley faces. Longer center distance may require wider belt or idler pulleys to maintain centering. The pictured application uses an 44 tooth XL belt. The two-step motor pulley has 5/16” bore and 15 and 30 teeth step pulleys. The spindle pulley has 5/8” bore and 20 and 30 teeth step pulleys. This provide either a 50% speed reduction or a 50% speed increase.
Synchronous drives are primarily used where angular positioning is provided by the motor axis rather than driven axis. This is common with stepper and servo motors. However synchronous belt has other advantages as compared with V-belt:
Higher power density enables smaller pulley sizes;
Longer belt service life;
Reduced belt tension - longer bearing life;
Reduced noise and vibration;
Reduced tendency for belt to take a “set” from storage periods.
As this is a startup business we do not yet have stock sizes. We expect to be able to offer stock sizes in the future at reduced prices. Please request a quote via email.
Pulleys are machined from pulley bar stock to match your exact specifications but, if you prefer, you can specify only belt size (width and pitch), pulley teeth and bore diameter and use our default specifications for other dimensions.
Our machining capability is currently limited to aluminum pulley stock with maximum of three pulley steps and 3 inch pulley diameter.
Note: Some free online web belt length calculators will warn if the smaller pulley does not exceed the recommended tooth engagement.
XL (1/5” pitch) 3/8” width belt size - 0.45” pulley face width;
0.1” spacing between pulley faces for guide taper;
Hub-less if larger pulley is under 2” diameter. If the larger pulley is 2” to 3” diameter a 2” diameter, 3.8” wide hub extension will be added to the larger pulley. A hub extension may be specified for smaller pulley diameters if set screw entry through the pulley face may be a problem.
A steel flange is added to the smaller pulley;
No flange is added to the larger pulley as it is generally not required. May be added upon request.
A single cup-face 10-32 set screw is added entering the larger pulley face or hub if a hub is specified. Additional set screws can be requested.
The pulleys are not machined for interchangeable components, but that can be accommodated upon request.
Request a quote using the following form.