How to measure and copy a broken gear?

Hello, i was given the following Gear for copying and 3d Printing. It is big 100mm diam. x40h mm

My doubt regards:

Measuring the diameters and number of teeth is the easy part.
But what about the other ones like module pitch and Pressure angle? How do i properly do this only with a caliper?

I use solidworks and rhinoceros. what gear generator would you recommend?

3 Answers

Sorting out this gear is a process of building up the details of this particular gear. Some details will come from careful measurement. If you know a bit about the machine it came from this may help you to know if it is a modern ISO standard metric gear or is it an imperial gear. Combining a bit of detective work and the information from careful measurement and details you will find in engineering texts on gears you will get to a point where you will have a reasonable idea of the probable gear details. I would then generate a gear model. From this I would print on paper a 2D of the assumed gear profile at 1 : 1 and lay the broken gear on top and compare, then if all looks good make the replacement.

As, going by your grabcad profile you come from an architectural background so probably don't have much of a library of mechanical design texts so I have included a document Gear Basics 1.pdf to help with your detective work

I would take a high resolution scan of the gear and use cad software to take the measurements, it will be hard to measure all the parameters with only calipers

Gear generator:

If the gear has a 100mm OD and 45 teeth it approximately matches Module 2 (Module = OD / (T + 2), I.e 100/47 ~ 2.12. Since module 2.12 is non-standard I suspect it might be the closest imperial size which is 12 DP (or module 2.117). Can't find an off the shelf 12 DP/45 teeth, but I do find module 2 gears with 45 teeth. There is a chance that it is a proprietary gear size of course.
The current industry standard for spur gears has a 20 degree pressure angle, but I guess it depends on how old the machine is.