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10/12 pitch?

10/12 pitch?

10/12 pitch?

So I was given a print with a gear on it and simply says 10/12 pitch and tooth number.

Does that translate into DP? Module?

Converting it to diametral pitch, Pressure angle, and # of teeth would be great.

RE: 10/12 pitch?

I think it is 10DP but with tooth height taken from DP12, most likely 20PA, close to AGMA stub.

RE: 10/12 pitch?

is there any other information like Pitch Diameter, Base Diameter, Major & Minor diameter, Measurement over wires, Max effective & Min actual circular tooth thickness?

RE: 10/12 pitch?

as well as my last post it should have # Teeth. Diametral Pitch & Pressure Angle

RE: 10/12 pitch?

@Spigor I've never heard of that. Wild... I just found this in a google search. Fellows Stub

"Another interesting system is shown in fig.6 it is the combination or split pitch system and uses the circular pitch and circular tooth thickness from one diametral pitch and the addendum and whole depth from another. On a gear of ¾ DP, for example, the gear is basically a 3 DP gear with the shorter addendum and whole depth for a 4 DP gear; hence, it is a stub form. Some caution should be used with this system of stub specification. ¾ DP has been mistaken for .75 DP, which is substantially larger in size."

What a pain in the rear to draw/program.

RE: 10/12 pitch?

A source I found said this:

In those cases where a pinion having a relatively small number of teeth must operate with a gear having three or more times as many teeth, a condition known as interference is sometimes encountered. Several solutions to this problem have already been given.

It then offers Stub gear profiles as a solution.

The underline above is my situation.

RE: 10/12 pitch?

@roark clearly you are newbie with gears.
Do not guess on the spline data.

This a most likely a spline.
The mating part is a female spline.

A correct drawing will specify
The required specification
Whether a gear or spline
Major and minor diameter.
True involute diameter tif or SAP
If a spline
Max effective tooth thickness
Min Actual

If you machine this wrong with the wrong geometry, it will not fit the mating part.
Strongly suggest you contact the customer
And obtain all of the information properly needed.

RE: 10/12 pitch?

Is this an internal gear set? Or is the pinion cut with a cylindrical tool rather than with a rack tool, e.g. shaped rather than hobbed?

A stub tooth form might address some problems encountered with small number of teeth on the pinion, e.g. excessive undercut and sharp pointing of the tip, as well as interference related. Many teeth would usually be required on the gear to get enough contact.

As some interference types can only occur in the internal meshing or when the pinion is cut with a cylindrical tool, no wonder that Fellows has invented their own stub tooth form.

Again I would recommend further reading of the DIN 3992 and DIN 3993 for good general info. My way of doing this is to perform a computer aided analytical inspection and a simulation of meshing to identify any possible performance and manufacturing problems and solve them.

Hope it helps.

RE: 10/12 pitch?

@spigor to what specification, it needs to be on the print.if it is a gear
What quality rating to which specification.
Involute, TCE, TTCE, pitch error, total pitch error, what tooth thickness,
The engineer should have specified the correct geometry.

RE: 10/12 pitch?


The interface drawing the supplier gave me for their product calls it a "pinion gear".

All it said was number of teeth and 10/12 pitch. That's it. Obviously not a "correct drawing" if I'm not able to interpret what they are talking about. I'm trying to get more out of them... but the part is old enough I'm willing to bet they are having to call people in retirement to explain it. Most of this stuff's last engineering action was in the 1970's. That's just how some of this old stuff is before AS9100 took over.

You are absolutely right. Usually on gears I have made include an entire AGMA data table in the drawing notes down to the dimension over pins inspection data. That said... "normally" If I know the big 3 (DP,PA,#T) and make them to a typical gear quality, there isn't much that a few extra thousandths of backlash won't solve in my world.

Do you have a theory as to what "10/12" pitch means with a possible design guide/specification?

RE: 10/12 pitch?

Absolutely, all that specs should be on the drawing, as stated in e.g. DIN 3966 “Information on Gear Teeth in Drawings; Information on Involute Teeth for Cylindrical Gears”.
But sometimes you get a drawing with very little information, and I believe that is the case in this thread.
Thank you for your good words.

RE: 10/12 pitch?


If they have no clue
Do you have a CNC checker?
Ask the customer to send you both parts
That mate.
Reverse engineer both details.
Inspect the major and minor diameter.
Count the teeth, inspect the gear profile visually. Optical comparator.
A must, verify both gears with a cnc gear checker.if you have the correct # Teeth, diametral pitch and pressure angle.
Then the involute profile will be straight.
Inspect the exact measurement over wires
Now calculate the exact tooth thickness.
If this is an American print try to match to a US specification.
Look at inspected pitch error, and involute. Match it to the correct AGMA.
If the print is metric then match it to
DIN or equivlant.
Ash gear in their catalog has different
Specification summaries.
Take a look.

If no parts available, then re-engineer both mating parts.but it can compound
If there is a gear train.
All parts have to roll properly.

RE: 10/12 pitch?

@spigor & @Roarks

in some cases the shop would machine to a standard stub pitch gear.
but they had specification to follow. I knew this spec. but I can't remember it. it's old. 1950 I believe.
10 Diametral pitch (teeth in diameter)
12 diametral pitch = addendum (stub pitch)

use the 10DP in the calculations only for Tooth Thickness & involute.
this could possible be a fellows stub pitch design.
but the customer should put this on the purchase order.
to indemnify the manufacture.

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