# How to generate involute gear milling Gcode

I need to make some gears/pinions myself. I have access to a high quality 4-axis CNC mill, but not to a lathe. I'd like to cut these gears out of flat stock (facing), rather than round (edgewise) using narrow end mills. Being able to prototype this in plastic sheets is important to me.

I've found a bunch of sites that explain hobbing and that have formulas for pitch etc, but no sites that actually generate the splines for the gear teeth to turn into Gcode.

Before I sit down with Mathematica and derive it from first principles, does anyone know of a good resource for this?

• I can't answer the question, but just remember that if the gears are to be used in an automotive application, they would need to be case hardened - this process causes the metal to shrink, meaning they have to be cut slightly larger to end up the right size. I've heard it described as "an art, not a science"!
– Nick C
Mar 26 '12 at 11:23
• That's a great reminder! Luckily, while used in my car, these are for an accessory, not power -- I'm not that ambitious :-) (At least not yet) Mar 27 '12 at 16:08

## theory

Some sites that I found useful in helping me understand why gear teeth are those funky involute curves, without getting bogged down in equations:

## practice

I hear a lot of people take this ".scad" script: "Parametric Involute Bevel and Spur Gears". They tweak the "number_of_teeth" and other parameters to their liking, and then use OpenSCAD to calculate all the involutes and other splines and show a solid model of that gear. Then they export a ".stl" sold model file and use RepSnapper or RepRapPro or Skeinforge or etc. to convert it to Gcode.

There's some example Gcode in Reyes's paper "Algorithm to Describe the Ideal Spur Gear Profile".

A few people somehow use a spreadsheet to generate the Gcode -- Ferreira "Using Spreadsheets to Parameterize Spur Gear Design for Laser Cutters" and Joe Martin "Plain gear tooth calculator".

Has anyone here used the delphusa "Gear-Wheel Designer with GCode Generator" ?

• It would have been great to have this answer a year ago :-) I ended up writing my own involute gear designer software: github.com/jwatte/gears Feb 12 '13 at 20:53
• Wow, thank you very much for posting that code online. I'm going to fork that code right now. Feb 13 '13 at 20:12