Sep 11, 2006, 08:56 PM Flying Extraordinaire United States, FL, Fort Myers Joined May 2006 69 Posts Discussion Measuring the pitch of a spur gear?? How does one accurately measure the pitch of a spur gear? I have a dc motor with a gear on it and want to get a corresponding belt gear that matches. I went to https://sdp-si.com/ but can't accurately measure the pitch to match to the correct gear belt. Any ideas? suggestions?
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 Sep 11, 2006, 09:21 PM Ascended Master Palmdale, CA Joined Oct 2000 13,621 Posts If you know who made the spur gear, ask them. Or find a matching gear whose specs are known.
 Sep 12, 2006, 12:53 AM Registered User Australia, NSW, Sydney Joined Feb 2003 1,114 Posts If it's for a toothed belt they only come in discrete pitches, 1/4, 3/8, 1/2 etc. So if you measure the distance between peaks you should be able to work out which one it is. The pitch diameter is taken below the outside diameter of the pulleys, but measuring on the peaks should get you close enough. Graham.
 Sep 12, 2006, 03:58 AM Registered User East Anglia, UK Joined Sep 2002 29,709 Posts Get some plasticene and roll the wheel over it. Count the distance and the toothpmarks. Do the Math.
Sep 12, 2006, 01:42 PM
Flying Extraordinaire
United States, FL, Fort Myers
Joined May 2006
69 Posts
What is plasticene? how hard would it be to make my own belt gear?? If I used putty as you say and roll the gear over it then I would have a mold correct? can you buy liquid rubber to make your own??

thanks

Quote:
 Originally Posted by vintage1 Get some plasticene and roll the wheel over it. Count the distance and the toothpmarks. Do the Math.
 Sep 12, 2006, 01:59 PM aka: A.Roger Wilfong Novi, Michigan, United States Joined Jan 2001 2,610 Posts Measure the diameter of the gear across the peaks of the teeth. Measure the diameter from valley to valley. Take the average of these two numbers - it will be close enough to the "pitch diameter" for our purposes. Count the number of teeth and divide by the "pitch diameter". Round to the nearest whole digit and you'll have the pitch. Plasticine is a form of clay similar to the kids modeling clay (not PlayDough). It is what the Aardman studio used to create the characters in "Wallace and Grommit", "Chicken Run" and the rest of their clay-mation films. - Roger
 Sep 12, 2006, 03:18 PM Registered User East Anglia, UK Joined Sep 2002 29,709 Posts I too thought of making my own belts..sadly what you need is a fairly complex composite of kevlar and rubber..best to just buy them. Moulding the cogs may not be so far fetched tho.
 Sep 13, 2006, 01:13 PM I like the violent stuff! Costa Mesa, CA Joined Oct 2004 1,291 Posts Vintage is on the right track. At work I roll it over a piece of carbon paper measure the distance between points and do the math.

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