View Full Version : how is a gear tooth vernier gage used???

03-20-2005, 12:39 AM
i'm not really thinking of bidding on this (and it will go for $250 now that i posted it here), but how the heck do you use one of these things?????


andy b.

Forrest Addy
03-20-2005, 12:59 AM
Using a gear tooth vernier caliper is easy enough. Set the gear's chordal addendum on the addendum vernier (works on the blade thingy) and straddle the gear tooth with the caliper. Bring the jaws together a tiny bit at a time till no free motion is felt when you wiggle the beam a trifle.

You use it to measure gear teeth, coarser screw threads (expecially Acme and square threads), thicknesses of bevels, etc.

Don't forget the mystery words "chordal addendum". That's the height from the pitchline to the tip of the gear tooth. The "chordal" comes in because you have to calculate the chordal height of the little arc subtended by the gear tooth at the pitchline and add it to the addendum. There's some discussion, a formula, and some tables in "Machinery's Handbook".

[This message has been edited by Forrest Addy (edited 03-20-2005).]

03-20-2005, 03:15 AM

There was an article some time back in HSM or MW on a simple adapter for a ordinary caliper to mimic this tool. You are right these go for stupid money! LK

03-20-2005, 05:05 AM
I have a book which gives a good formula for measuring across a few teeth at a time, all you need is a micrometer with disc type anvils to get between the teeth, much cheaper than a gear tooth vernier.
Also be aware that the vernier is not good at measuring fine pitch gears, it is just too bulky, so if you are into the smaller stuff, forget it.

John Stevenson
03-20-2005, 06:42 AM
When you really get bit by the gear bug you NEED one of these http://bbs.homeshopmachinist.net//biggrin.gif


Ideal for geriatric gear heads with lens's like coke bottle bottoms.

John S.

BTW. I always thought a Geriatric was a German fast bowler?

Spin Doctor
03-20-2005, 06:45 AM
One word of warning about Gear Tooth Verniers. They have a 20 division vernier scale insteadof 25. Found out the hard way http://bbs.homeshopmachinist.net//eek.gif

Alan in Oz
03-20-2005, 07:24 AM
This link may be useful http://www.omnigearandmachine.com/gear_tooth_verniers.htm

03-20-2005, 08:07 AM

you just blew my mind.

John S.,

i wouldn't even want to guess at what that contraption costs.


i need to find me a book on gears and figure this out.

andy b.