Does this exsist?

Do you want to determine the module?

Do = (N + 2) * Mod

Do: Outer Diameter N: Number of teeth Mod: Module

Or to determine the wear:

Nick, too lazy to go to tinyurl.com

That formula does not give me the answer in Mod or DP or does it?

Another baddie in this is that I can have say a 10-12DP gear.

The teeths are one DP size and the OD is the other DP size.

I can't see how that gives me the Mod or DP of the gear.

The point is that I have both Mod and DP and absolute no marking on the gears :-(

Found this for calculation:

And this: But direct measurement of one single teeth? No.

Uffe, go here:

If you go to the Technical Section, you can download the entire PDF catalogue, around 43Mb, or order a printed one. Alternatively, go to the Spur Gear page and select either Module (metric) or DP gears from the pull down menu, then select the size.

This will bring up a PDF of the catalogue page, and on each page they print a silhouette of the tooth form at actual size. If you print the page with the PDF scaled to 100% this will give you a rough and ready gauge of sorts.

Peter

And now, after some shuffling around?

Mod = Do / (N + 2) But this doesn't help to determine wear. You can only determine the module. After that and a book like "gearcutting practice" you can determine the wear (width of tooth changes) with the aformentioned "funny caliper".

Nick

Just to clarify my answer: It does give you the module of the gear. There are exceptions when the gear does have a modified profile. Normally, you don't find that. Except in car's gearboxes or other highly specialized gears where there are extreme loads with a little number of teeth and/or several gears are crowded on one axle. But then, you could always use the ... ummm ... howsitcalled ... the medium diameter (average between OD and ID at tooth ground). Face diameter? Too lazy to look that up. :-)

Ni-lazy sunday-ck

Pitch Circle Diameter. Where the contact path crosses the line joining the centres.

You mean gear tooth gauges ? That's what it reads like to me but no one else has picked up on this ?

or

John S.

In North America, the Boston Gear Company can supply gear tooth/pitch gauges through their dealers. Their catalogue also has a printed one that can be of some use.

Steve R.

It just came to my mind: If you have two gears that mesh, you can determine the module more accurate by measuring the distance of the centers.

a = (Z1 + Z2) * mod

a: distance of centers (axles) in [mm] Z1: Number of teeth of gear 1 Z2: ... of gear 2

mod = a / (Z1 + Z2)

The method with the gages isn't very accurate. There are DP and Mod sizes that are quite near to each other, and you'll have problems determining of which breed it is.

Nick

That assumes that the two gears have been accurately meshed so that their PCDs just touch. Not always a good assumption.

Regards, Tony

But better anyhow than assuming that the OD is accurate. At least I assume so. :-)

Nick

That's not at all clear ;-)

Regards, Tony

If they're that close, does it really matter which (depending on the application, of course)

...and of course there are CP sizes, too ;-)

Tim

Having arrived at the size of the teet how do you decide what the pressure angle is. I need to do this as I have a spur gear to make for a vintage car speedo drive and I know that often a pressure angle of

14 1/2 degrees was used in the 1920's

Roll the gear through modelling clay and measure the angle of the teeth of clay rack, this is the PA Peter

Elegantly simple; thanks.

marking on the

And made even easier if you then cut the clay rack with a craft knife along its length to give a clean edge that you can look at with one of those graticule eyepieces. The difference between 14 1/2 and 20 PA is easily seen.

AWEM

Thanks. I will have to take a closer look at those. It looks like what I'm asking for :-)