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Old Sep 11, 2006, 09:56 PM
Flying Extraordinaire
United States, FL, Fort Myers
Joined May 2006
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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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Old Sep 11, 2006, 10:21 PM
Ascended Master
Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
13,499 Posts
If you know who made the spur gear, ask them.
Or find a matching gear whose specs are known.
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Old Sep 12, 2006, 01:53 AM
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Australia, NSW, Sydney
Joined Feb 2003
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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.
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Old Sep 12, 2006, 04:58 AM
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East Anglia, UK
Joined Sep 2002
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Get some plasticene and roll the wheel over it. Count the distance and the toothpmarks. Do the Math.
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Old Sep 12, 2006, 02:42 PM
Flying Extraordinaire
United States, FL, Fort Myers
Joined May 2006
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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.
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Old Sep 12, 2006, 02:59 PM
aka: A.Roger Wilfong
gnofliwr's Avatar
Novi, Michigan, United States
Joined Jan 2001
2,550 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
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Old Sep 12, 2006, 04:18 PM
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East Anglia, UK
Joined Sep 2002
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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.
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Old Sep 13, 2006, 02:13 PM
I like the violent stuff!
Costa Mesa, CA
Joined Oct 2004
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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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