Gallery, Projects and General > How do I??

Involute Gears - Identification of Pressure Angle.

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Pete W.:
Hi there, all,   :mmr: 

N.B.:  this is NOT a 'for sale' posting!

I am having a 'spring clean' in my workshop    :clap:   :clap:   :clap:   :clap:   :clap:   :clap:  and have discovered a number of gearwheels that are surplus to requirements.  I am about to compile a description prior to listing them on a well-known auction site and I like my listing descriptions to be complete and accurate.

I know how to determine the D.P. (they are Imperial) of these gears and measurement of the thickness and centre hole dimensions is straightforward.  I would like to include the pressure angle in my description.  However, I have no idea how to measure that parameter.   :scratch:   :scratch:   :scratch:   :scratch:   :scratch:   :scratch: 

Wikipedia states that 20° is the usual value but that 14½° is a less common value.  I have read that both values are found on various lathe gearwheels.

So, my question is: is there a simple measurement procedure, using equipment I am likely to have, that would enable me to distinguish between 20° and 14½° pressure angle?  (I do not possess a gear-tooth vernier gauge.) 

DMIOM:
Pete - not sure if they're any use but have a look at this or this (courtesy Mr Google)

Dave

Pete W.:
Hi there, Dave,

Thank you for your reply.   :bow:   :thumbup:   :bow:   :thumbup:   :bow:   :thumbup: 

I had done a Google search but I missed those links. 

The first one looks like the way I should go - just a vernier caliper, a pencil, the back of an envelope and, if a senior moment blitzes my arithmetic, break glass and deploy the slide rule!    :D   :D   :D 

Lew_Merrick_PE:

--- Quote from: Pete W. on September 02, 2013, 08:41:04 AM ---Wikipedia states that 20° is the usual value but that 14½° is a less common value.
--- End quote ---
Which should warn you about Wikipedia -- 14-1/2° PA was the primary standard for inch-based gear well into the 1970's.  20° PA entered usage during WWI, but did not become common for gear until the early-/mid-1960's.  One of my premiere screw-ups as an apprentice was failing to recognize the difference (because apprentice texts of that time assumed 14-1/2° PA as a matter of course).

Pete W.:
Hi there, Lew,

Thank you for that warning.

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