Identifying Spur Gears

I have a bag of assorted small spur gears, some steel, some fibre, up to about 1.25in od and up to ½in bore. But whilst I can count the teeth I have no idea of how to identify them any further.

Can anyone tell me how to identify them please, what to check, etc?

Chris

If they are metric, divide the diameter in mm by (number of teeth+2) to get the module.

If imperial, divide (number of teeth+2) by diameter in inches to get the Diametric Pitch.

If you have meshing gears they should give consistent results (allowing for errors in measuring outside diameter, especially on gears with an odd number of teeth).

Note that gears can be undersize and some metric and imperial sizes are very close (25 dp is near to 1 mod, for example).

Rather harder to check things like the tooth angle, except by comparison with known gears.

Neil

Edited By Neil Wyatt on 25/11/2014 17:52:38

Hi Chris,
There was a very good article in MEW 158 (December 2009) on making gears.This details most of the formula to do with gears. If you use the relationship between the number of teeth and the tooth tip diameter you should be able to work out the modulus or DP value. I used this to identify modulus 1 gears in assorted boxes of gears at model engineering exhibitions to get some more gears to use for screw cutting a greater range of threads.

Les.

Hi, thanks Neil and Les. With your help and reference to MEW 158 have managed to determine my little gears are DP 36 and with a PA of 14.5degrees so far, so well on the way with them. Thanks to you both,

Chris

Hi Neil,

Just FYI the correct term is diametral pitch, not diametric pitch, for inch size gears. May as well get the nomenclature correct.

Ready now for the usual mass accusations of anorak-ness and pedantry.

Cheers JD

Should that be Anorakal-ness?

:0)

Martin

A friend of mine once described to me a particularly boring lecture on a hot summers day while on day release course at the local college, where he fell asleep. When, on being woken by the lecturer and asked, "well, what is a spur gear then lad?" his quick witted replied was, "the one you've got left over sir!

A year or so ago someone produced a series of silhouettes of each gear, I can't find it, put in "gears" in the search panel, and you get 3 pages of threads.

Ian S C

Contact HPC gears, they used to be called Hinchcliffe Precision Components, they have a wonderful catalogue with thousands of gears in it. Both Imperial and metric, all you need to do is measure your gears and compare with theirs. There are many charts of the different sizes available. The staff are extremely helpful. Hope this is some use. Martin R.

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Jeff,

In times when even the O.E.D. is letting us down; it's good to see you trying to preserve the English language.

MichaelG.

Another feature of the HPC catalogue is that it has silhouette outlines of all the gear teeth profiles.

Google for 'HPCGEARS' and you should find their website.

Ian P

The Davall Stock Gears catalogue is good too.

The OED reflects English as she is spoke, not as she should be!

And as far as diametric/diametral - neither of them is in the OED anyway! Colllins (which always gives more useful definitions (rather than origins, IMHO) than the OED) says diametral is a less common word ffor diametric.

:-P

Neil

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Oh ... what's this ?

MichaelG.

Hmm, not in the non-subscriber online OED as far as I could see, though.

Neil