How critical is tooth count on the pulleys?

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How critical is tooth count on the pulleys?

Postby jkittle99 » Thu Mar 21, 2013 1:48 am

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

Postby BenJackson » Thu Mar 21, 2013 3:14 am

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

Postby Cre8ivdsgn » Thu Mar 21, 2013 11:37 am

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
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Re: How critical is tooth count on the pulleys?

Postby bdring » Thu Mar 21, 2013 1:30 pm

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.
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"If you didn't build it, you will never own it."
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Re: How critical is tooth count on the pulleys?

Postby jkittle99 » Fri Mar 22, 2013 12:29 am

Some very good information. Thanks guys!
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Re: How critical is tooth count on the pulleys?

Postby StigOE » Fri Mar 22, 2013 12:04 pm

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.
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