## How critical is tooth count on the pulleys?

Questions, Suggestions, Tips, Etc

### How critical is tooth count on the pulleys?

So the subject is fairly self explanatory. As long as I'm cool with using the belt calculator to get the numbers for mm/step, do I really care what tooth count the pulleys are, is close (18 vs 20, etc) going to be close enough? Obviously the math has a few less decimal places when the numbers are a factor of 10, but does it really matter?
jkittle99

Posts: 13
Joined: Tue Mar 12, 2013 6:19 pm

### Re: How critical is tooth count on the pulleys?

It did for some particular controller that could only configure a limited number of steps/in values (like 0.001" / step). For a better controller this is not an issue.
BenJackson

Posts: 522
Joined: Fri Apr 15, 2011 6:13 pm

### Re: How critical is tooth count on the pulleys?

Regarding tooth count:

The larger the tooth count, the greater the pitch diameter and the more torque the motor needs to accelerate to a velocity. A 20 tooth is 0.509" and an 18 tooth is 0.459". This is an 11% increase in pitch diameter. My kneejerk thought is that for Hadron-style systems this is trivial relative to the torque the NEMA 17 motors typically produce.

Parker Daedal had a great catalog of motion systems with a workbook appendix for various motion styles. And of course Pacific Scientific (now Danaher) has a great motion package to calculate torque requirements and do motor sizing. http://www.kollmorgen.com/en-us/service-and-support/technical/motioneering/

My 2 cents
Cre8ivdsgn

Posts: 52
Joined: Mon Aug 15, 2011 12:42 am

### Re: How critical is tooth count on the pulleys?

The torque is not an issue with reasonable values as long as the acceleration on the parts does not change. The only issue is resolution.

You want the belt to run reasonably parallel to the track or the resolution and tension would vary with position. If the pulley is much larger than the idler to would be a problem and the point where the belt attaches would be a problem.
Bart
"If you didn't build it, you will never own it."
bdring

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Joined: Sun Nov 22, 2009 7:33 pm
Location: Chicago, IL, USA

### Re: How critical is tooth count on the pulleys?

Some very good information. Thanks guys!
jkittle99

Posts: 13
Joined: Tue Mar 12, 2013 6:19 pm

### Re: How critical is tooth count on the pulleys?

BenJackson wrote:It did for some particular controller that could only configure a limited number of steps/in values (like 0.001" / step). For a better controller this is not an issue.

I think the controller you're referring to is the RetinaEngraveUSB, but this has been rectified in later software/firmware versions.
StigOE

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Joined: Thu May 12, 2011 9:08 pm
Location: Norway