# How can I create WORKING gears in Illustrator?

## How can I create WORKING gears in Illustrator?

### Question

I cannot seem to get this right.. I want to create 2 gears that **work together**.

I can create gears, but I cannot seem to figure out the math needed to make them **uniform**, or where they *work together*.

**There is a mathematical way to do this.** I do not know the formula..

# What I'm trying to accomplish.

**What I tried:**

- Create a circle
`800px x 800px`

- Create a circle
`600px x 600px`

- Create a star with inner radius 200 (400 diameter), 500 (1000 diameter) outer, with 12 points.
- Compound the smaller circle and star. Intersect the remainder.

Do the same thing, except **half each value and the points**.

I would think this would make a 2:1 gear ratio where both gears match exactly, but they don't...

### Accepted Answer

The same way one would create a real working gear. Here are tools which will create gears:

- http://geargenerator.com --- this tool will allow one to save an SVG which can be edited in any vector drawing program
- http://sourceforge.net/projects/gggears/?source=directory --- opensource tool
- http://www.idleamusements.com/?page_id=367 --- an on-line tool, it will create a .dxf which can then be opened in Illustrator
- http://www.cabinetpartspro.com/GearMaker/GearMaker_Setup.exe --- Windows tool

See the site http://woodgears.ca/ for more information on gears --- they have a Gear template generator as well: http://woodgears.ca/gear_cutting/template.html

Alternately, you can draw them by hand --- you just need to use basic geometry to ensure that the diameter of each gear is an integral ratio.

### Popular Answer

I'm not a graphic designer or user of Illustrator, but I am a mechanical engineer. I won't bother going into the details of a properly engineered gear, but just how to get yours to "look right".

Your teeth do not have the same depth as each other because you are simply cutting all your dimensions in half. Instead, the bases and tips of the teeth need to be the same distance away from each other in both sizes of gear. The dimension that should be cut in half is the diameter of the "pitch circle".

The pitch circle is somewhere between the tips and bases of the gears. You can just put it halfway between for your purposes. (In properly designed gears for minimal noise and backlash, etc., there is a complicated formula to determine where to position the pitch circle and how to contour the teeth accordingly--see @joojaa's answer.)

So for the big gear where the two circles are at 600 and 800 diameter, your pitch circle is 700 in diameter with the tips and bases +/-100 in diameter. So your small gear should be 350 in diameter with the tips and bases +/-100 in diameter. Therefore, your small gear should use circles of 250 and 450 in diameter.