I just want to make a gear
I Just Want to Make a Gear...
Andrew Prestridge | September 8, 2020
The invention and perfection of the involute gear is one of the least heralded advances in mechanical engineering. Due to their essential function (transmitting torque and movement) they are hidden deep inside castings or shrouded with protective covers. Out of view, the modern gear is doing more than ever as we have challenged designers to transmit more torque, in lighter packages, while running quietly, and at the same time cost less. Luckily, good designers, materials, and better and more accurate gear processing equipment have been able to continue this path for high-end applications.
Finite Element Model of a Spur Gear
And How to Take Advantage of It
But what if you don’t work for GM, Ford, Chrysler, Tesla, or Big Industry? How could an individual possibly take all the accumulated millennia of knowledge and make their own gears? How can the Maker Movement include gearing in their toolkit? How can we get a grip on gears that have many tall hurdles and slippery rabbit holes where one can get lost?
CAD and machine tools have been rapidly increasing in capability and decreasing in cost, so the ability to mill, route and 3D-print gears is in reach to a larger audience. So how do I get started? Here are some simple answers:
The Math-free Path
If you own a 3D-Printer, it comes down to finding a file (.DXF, .SFG, .STL, .STEP, or others) of a gear that you would like to print. We created a free gear generator for your use. The next step is setting up the center distance between two gears you have printed to get them to mesh properly. You can do this through a calculator or by feel like most watchmakers.
If you own a CNC router, the pathway is identical to the 3D-printer process, use a compatible filetype (2D or 3D), load a sheet of plywood/plastic/brass and you are on your way.
The Involute Curve (…and the math begins)
Just knowing the terminology “involute” you are way ahead. This is the shape of the meshing gear surface that allows gears to roll (and not slide!) The rolling characteristic of gears is a realization in history dating back to at least 1500AD and involves the famous mathematician Euler. This is where the math starts to creep into the making process and this is the first big hurdle. If you cannot find your gear online in a format you like, you may want to create one from scratch with a CAD program. The formulas are actually not too difficult, and you can make a parametric set of variables that will draw gears of any tooth count.
Gear Blank Size and Quality Control
This is usually the hurdle that is steep enough to halt most in their tracks. And you must know it if you are to design the gear blank dimensions for many processes. Our Gear Dimension Calculator in conjunction with the Measurement Over Pins calculator will enable you to make gears AND QC them so you can dial-in your process.
Measurement Over Pins - A Key Quality Metric
Profile Shift Correction or Addendum Modification
This is the next step in the understanding of gears and relates to backlash, profile angle, gear mesh etc. These variables allow designers to make enhanced designs for gears that lead to stronger and quieter gears in mesh. This is the start of another level of skill that you can learn more about in our MOP blogpost.
|Process Equipment||Drawing of Gear Outline & Tooth Count (involute is in the drawing)||Involute is in the cutter||Gear Blank Dimensions||Knowledge of Pressure Angle, Tooth Count, Tooth Form (Involute||Profile Shift Correction, or Addendum Modification on Specification||Machine Tool Setup, CAD/CAM Toolpath|
|Watchmaker, lathe, files||YES||NO||YES||NO||NO||NO|
|CNC Gear Hobber||YES||YES||YES||YES||YES||YES|
|CNC Gear Grinder||YES||YES||YES||YES||YES||YES|
Bold-Italic: Our Spur Gear Generator creates the .DXF and .SVG files for upload into your machine or CAD/CAM program.
Bolded: Our Gear Dimension Calculator solves Involute math for you and is helpful in these areas of gear processing.
*Making plastic gears from a mold is a process, but the mold making of the original gear originates from one of the above processes
Making a Gear
Use a Generator
Using a gear generator is the easiest way to make a gear without specialized equipment
Buy a Cutter
Machine tools may have bits or cutters that have the involute gear form built in
Inspect and QC
Using Measurement over Pins can tell you if your gear is the right size and shape