Gear control measurements don't conform

[perilous]

Hello.

As you know there are two main methods to control gears after production, over pin and gear span measurement. I checked these two on a gear produced in our workshop. The Wk for three gears was OK but over pin had the unconformity in the scale of 0.5 mm! Where is the problem? What do you think?

 

[perilous]

Actually I was to meant to say I'd measured Wk for 3 "teeth"!

 

[spigor]

Did you count the teeth in the gear?

 

[perilous]

Yea of course. All the parameters seem to be correct. The W3 is correct!

 

[israelkk]

Can you provide the gear drawing with the requirements as they appear in the drawing? How the gear was manufactured?

 

[spigor]

Is the difference 0.5 mm exactly? This is the common reading error with some caliper designs.
Are you sure the MOW and span dimensions are calculated correctly?

 

[gearcutter]

Several things can cause this; here are some issues that I've encountered -

1. Incorrect pressure angle was cut (gear cut to the correct BTL but MOP will be different).
2. Measuring a helical gear.
3. Measuring a helical gear with an odd number of teeth (more-often-than-not, the calcs for MOP have been done incorrectly).
4. Using pins instead of balls (this becomes more obvious as the helix angle increases).

 

[gearcutter]

I forgot to add one -

5. If a helical gear; are your MOP calcs done in the transverse or normal plane? Most calcs/specs call for the measurement to be taken in the transverse plane.

 

[mfgenggear]

Gearcutter

In American the most common dim's are specified in English & the dim's specified in the Normal Plane.
including Measurement over wires. MOW checks are more common in the USA.
The # teeth,Normal DP, & Normal PA & helix angle. the computer will automatically compute the necessary adjustments.
it is true for ODD # of teeth the MOW will be specified on 1/2 of the MOW.
because of the inaccuracy with two pins.

Perilous
that said to reiterate Gearcutters comments are correct about Geometry.
in other words the M.O.W. is only one attribute. the lead, the Involute & TCE (Total Composite Error), must be inspect as whole. you could have the correct M.O.W. but incorrect involute. depending on the the manufacturing method.

Are the Inspection tools calibrated. are the balls or pins calibrated.
verifying span measurement or MOW is a very simple and precise method.
I prefer MOW. because it was prevalent in the USA.

Mfgenggear

 

[mfgenggear]

I forgot to add if the involute & lead are correct then the DP and pa are correct.

Mfgenggear