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Securing pulley to stepper motor shaft

Securing pulley to stepper motor shaft

Securing pulley to stepper motor shaft

A stepper motor with a 5mm shaft was specced and passed along to me to affix a 14-tooth pulley to. The motor has a flat machined on the shaft and is clearly set up for a setscrew-style attachment. Additionally, the pulleys in the correct sizing also use setscrews. This is a problem because although I am familiar with design fundamentals for keyed shafts, clamping shaft collars, and other similar methods of securing components onto shafts, I have never worked with setscrews in this application. I am having trouble finding any literature on the design of setscrew couplings beyond just disparaging articles or passing references in textbooks to a torque spec. The pulley will be driven back and forth rapidly and is a critical component for the larger system so I would not feel comfortable just affixing it with any old setscrew and without a proper design process to prove that the connection is adequate.
Essentially, what I am asking is
- Is there any literature for proper design of setscrew shaft attachments that I am just missing?
- Do you have any suggestions or input on best practices for such an application?
Thank you!

RE: Securing pulley to stepper motor shaft


I hate set screws. On something that runs continuously, they may be adequate. I would never trust them on an actuator. You did write "stepper motor".

Search the W.M Berg, Nordex, PIC Design, and SDP/SI catalogues for clamp type hubs. You ought to be able to attach your pulley using unmodified off-the-shelf parts.

Note how many if not most of the components in these catalogues are interchangeable with the other vendors.


RE: Securing pulley to stepper motor shaft

I hate set screws as well, they always seem to be a worse way of doing something that has already been correctly solved. It's on a stepper motor indeed and it's supposed to move back and forth relatively rapidly (5Hz or so), so I really don't like the idea of using a set screw in general even with a flat on the shaft. Thank you for the recommendations, I'll take a look at each of the sites!

RE: Securing pulley to stepper motor shaft

Fun Misumi video.

I don't think The style and assembly orientation of the key at 1:13 was vetted by any of their engineering groups.

Similarly, the resting place of the taper lock at 1:50 looks way too deep.

RE: Securing pulley to stepper motor shaft

Machine design is not my bag, I will take your advice. however interesting video yes, at least gives quick options.

RE: Securing pulley to stepper motor shaft

The attached info from Unbrako is a start.

Note the "holding power" was defined as .010" relative movement of shaft and collar.
For my money whatever it means that is a BIG FAIL.

Where does the recommended dynamic situation factor of 8.0 compare to your best estimate of actual loading ?

RE: Securing pulley to stepper motor shaft

How about drilling a small hole on the shaft flat area and a split spring dowel pin? It will take care of both circumferential and axial movements.


RE: Securing pulley to stepper motor shaft

There are shaft locking compounds that are good for this.

RE: Securing pulley to stepper motor shaft

The small diameter and D shaft really limit your pptions. Is the pulley hub metal? If so, I'm with Dave, use a retaining compound and forget the set screw. A primer should be used to improve the strength, especially if any components are aluminum.

A second option, if your pulley has an unfinished bore, is to run an interference fit.

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