Modifying AT pulley for reduced backlash

[David Child]

It's a bit of an off-the-wall idea, but has anyone considered skimming the outside diameter of an AT pulley to reduce backlash?

If you look at this diagram on the Brecko website, it is clear that the belt tooth peak does not contact the bottom of the pulley profile with standard T pulleys and the belly valley has a more substantial clearance on AT pulleys.This is in stark contrast to the reduced and zero backlash pulleys.

So, for a rough but hopefully effective solution, reduce the peak of the pulley profile so that the belt bottoms out fully and there is more belt valley clearance.

In the AT design specs, the belt teeth are supposed to bottom out. I presume they don't in a standard pulley due to either lifetime concerns or manufacturing tolerances or both.

https://www.brecoflex.com/blog/timing-belt-and-pulley-backlash-reduction#:~:text=Pulleys%20with%20Reduced%20or%20 Zero,many%20T%20and%20AT%20pitches.

32571

[EddyCurrent]

Are you actually seeing backlash on your pulleys ? it's not something I've noticed or thought much about.

Edit: I've just seen the older post by Muzzer on this topic.

[David Child]

Are you actually seeing backlash on your pulleys ? it's not something I've noticed or thought much about.

Edit: I've just seen the older post by Muzzer on this topic.

To clarify, yes, I have substantial backlash on 5mm HTD pulleys. On researching, I found that the lowest-backlash toothed belt drive is AT profile and that the pulleys are available in three quality standards: standard, reduced backlash, and zero backlash.

The problem is I can't find a stockist of the sizes I want in zero backlash, and the ones that are available are an eye-watering price.

Hence my inquiry re skimming standard AT pulleys. It appeared from the manufacturer's schematic that the most significant difference between the 3 qualities is that the belt tooth profile progressively "fills" the pulley tooth profile as the backlash reduces. ergo, skim the pulley to make less volume available in the pulley tooth profile forcing the belt tooth to fill the available area.

I assume there will be downsides, probably reduced belt service life, but at my usage rate, that's a compromise I'm happy to make.

Cheers

[Muzzer]

No harm in trying and seeing what happens. The crappy pullies I encountered were not designed to have backlash - they were simply very poor quality. The tooth profiles should result in zero backlash out of the box. I suspect most of the hobby / commodity products we see on the market are made from extrusions made by a small number of producers, so are of similar, indifferent accuracy. On the other hand, true professional industrial products cost an arm and a leg but that cost is fine for the end users. Interesting that they sell 3 grades, when clearly only one of them actually meets the specification!