Involute Gears - Identification of Pressure Angle.

Gallery, Projects and General > How do I??

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awemawson:
Take the gear, roll it in Plasticine to form a rack. Cut along the length of the rack so you can see the profile in elevation. Measure the angle

drmico60:
I have looked at ways of identifying the pressure angle of gears. The simplest procedure is to roll it in plasticine, slice through the impression and measure the angle. When I tried this it did not work very well for two main reasons:
1. On the gears I was trying to identify (mini-lathe change gears) the plasticine would not pull away cleanly from the gear when trying to make an impression. Often material was left between the teeth of the gear or the impression was distorted.
2. Cutting through the impression also causes distortion and the measured angle can differ depending on the direction of cut.
In the end I resorted to a photographic method which is outlined on this webpage:
http://mikesworkshop.weebly.com/change-gear-pressure-angle.html
This method seems to give good results and will positively differentiate between 14.5 degree and 20 degree gears.
Mike

BillTodd:
One quick way , if accuate id is not important i.e. a beer bet, is to look at the root of the teeth, if the root is square shaped it usually means it's a 14.5PA gear .

Bill

awemawson:

--- Quote from: drmico60 on September 02, 2013, 12:13:34 PM ---I have looked at ways of identifying the pressure angle of gears. The simplest procedure is to roll it in plasticine, slice through the impression and measure the angle. When I tried this it did not work very well for two main reasons:
1. On the gears I was trying to identify (mini-lathe change gears) the plasticine would not pull away cleanly from the gear when trying to make an impression. Often material was left between the teeth of the gear or the impression was distorted.
2. Cutting through the impression also causes distortion and the measured angle can differ depending on the direction of cut.
In the end I resorted to a photographic method which is outlined on this webpage:
http://mikesworkshop.weebly.com/change-gear-pressure-angle.html
This method seems to give good results and will positively differentiate between 14.5 degree and 20 degree gears.
Mike

--- End quote ---

Talcum powder on your gear will cure the sticking. Placing the impression in the freezer before cutting will cure the distortion.

(I do the same with side of bacon before slicing them works wonders. A side of bacon needs about an hour in the freezer but I can't quote a time for plasicine !!)

Pete W.:
Hi there, Andrew,

Thank you for your suggestion.

--- Quote from: awemawson on September 02, 2013, 11:51:40 AM ---Take the gear, roll it in Plasticine to form a rack. Cut along the length of the rack so you can see the profile in elevation. Measure the angle

--- End quote ---

It had me flummoxed for a few minutes - where on the rack would I measure the angle? :scratch: :scratch: :scratch:

Then the penny dropped. You don't wrap the Plasticene around the gear - you roll the gear along the Plasticene.
So you're regenerating the rack appropriate to that DP gear, which for involute gears is a straight sided rack!!! :thumbup: :thumbup: :thumbup:

OK, I've got it!!! Thanks.

Thank you also to everyone else that has contributed. :mmr:

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