Science/Engineering/Technical forums

Hi, for my cnc router project I need to make three tooth belt pulleys but I am not quite sure of how to go about. I have made a kind of poor man's dividing head using cog wheels from my lathe which I believe is quite accurate. I don't seem to succeed with making a pulley that fits the belt. I get it just a few percent wrong. Now, I don't have any data for my belts cause I scavenged it from an old printer. Measuring the tooth division I get about 2.036 mm. I guess it's a 0.8 inch division which seems to be a common Standard. What outer diameter should I calculate to use, is the fact that the belt is bend around the pulley affect the division? There must be a offset position inside the thickness that the bending does nor create compression, nor expansion and that is where I should calculate the pulley diameter from? Something like d = ( n-cogs * division) / PI + 2* offset. Any one knows?
Thanks, Lars

Seriously, just buy the pulleys, they are cheap. I have seen people make their own and they never work as well. The groove profile changes depending on the number of teeth just like a gear.

I like sdp-si.com Good prices and quick service. Plastic ones will be more than enough for most any cnc machine, I have built a lot of them.

Thanks Jerry, I am starting to realize that is the best option after all trials and failures. The link you send seems to have everything. Nice, they even ship abroad. I have not found a good supplier in Sweden yet but there must be, shipping two small pulleys from US seems like a bit overkill.

Shipping from the US can be cheap if you just use the US mail - but it takes forever, as in "slow boat" - 2 months or so. UPS and Fedex are a lot faster, and a lot more expensive.

With all the vendors I deal with, I generate a wish list and hold off ordering till my list is a decent size. Sometimes holds me back a little bit, time-wise, but it helps with that issue. I do save money that way - sometimes some of the stuff on the list I realize I didn't need by the time I finally make the order!

For the curious reader I found this good paper on calculations on tooth belts and pulleys: http://www.aratron.se/file/9berakning.pdf

You can also use Gearotic to figure the profile.

http://gearotic.com