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Old 14-03-18, 08:50 AM   #1
Dan_pt
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Default Working out what gear to order.

Hi, I need to replace the magneto gear on a Ruston APE as it has two damaged teeth. I have looked on the HPC website and I need to work out the DP of the old gear to order a replacement. Do I measure the distance between the teeth or is there a formula I need to work to or is it a case of the number of teeth Vs the diameter? Sorry if this is a silly question but I don't want to order the wrong one!

Dan.
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Old 14-03-18, 09:33 AM   #2
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What is the outside dia and number of teeth, from that I can look up the DP and pitch dia.
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Old 14-03-18, 09:34 AM   #3
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All you need is the Outside Diameter & the No of Teeth.

OD = (N+2)/P

OD = Outside Diam
N = No of Teeth
P = Diametral Pitch (DP)

For Metric gears

Module = 1/DP
And therefore Module = OD/(N+2)

Hope that helps !
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Old 14-03-18, 10:19 AM   #4
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Thank you for the help. I will measure it later on.

Dan.
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Old 14-03-18, 10:31 AM   #5
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Quote:
Originally Posted by Dan_pt View Post
Hi, I need to replace the magneto gear on a Ruston APE as it has two damaged teeth. I have looked on the HPC website and I need to work out the DP of the old gear to order a replacement. Do I measure the distance between the teeth or is there a formula I need to work to or is it a case of the number of teeth Vs the diameter? Sorry if this is a silly question but I don't want to order the wrong one!

Dan.
Do HPC still do a paper catalogue? It used to have useful full scale silhouettes of various tooth profiles which was a big help in identifying.

NHH

Last edited by nickh; 14-03-18 at 11:37 AM.
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Old 14-03-18, 10:40 AM   #6
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I have no idea Nick. I just looked at their website. The gear I need is under 2" diameter so should be quite reasonably priced. Hopefully all tht will need doing to the new gear is to have a taper machined into it to suit the magneto shaft.

Dan.
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Old 14-03-18, 11:26 AM   #7
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I was also wondering about the paper catalogue, the printed tooth profiles are very useful. Not least because there is another variable; gear teeth also have a pressure angle, and they're not all the same.

I have found the HPC gears are very high quality but tend to be quite thick. There's a fair chance you will also need to slim it down a bit.

MP
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Old 14-03-18, 05:59 PM   #8
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I have measured my gear and it comes out at between 1.77 and 1.8 inches depending on where I measured it

Using the above formula it comes out at 10 DP. Does that sound right?
It has 16 teeth.

Dan.
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Old 14-03-18, 06:19 PM   #9
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Based on your info, HPC gears list one, their G10-16 comes in at 16 teeth and 1.8 in diameter, 21 ish....plus carr

A 10 dp gear cutter in hss is about the same price....if you got a mill and indexer to make your own gears....

Last edited by Chippie; 14-03-18 at 06:21 PM.
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Old 14-03-18, 06:20 PM   #10
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Looking in the Machinery Handbook it is 10 DP.
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