One of the most difficult and yet common mechanical systems is a gear train. A great way to transmit mechanical power from one place to another or to increase or decrease power (torque) or increase or decrease the speed of something.

The problems are always that to make efficient gears needs quite a lot of drawing and mathematical skill as well as the ability to machine complex shapes.

For a lot of amateur work it isn't necessary to have maximum efficiency and therefore we can get away with a much easier to make, even with hand tools, system.

A gear is basically a series of teeth on a wheel.

http://automata.co.uk/gears.htm

provides a very good explanation of how gears work and how to work out gear ratios.

(Note in the diagram above they have labeled an incorrect number of teeth on the gears - sorry)

Step 1: Formula and Maths (the Bad News)

Formula for drawing and making gear teeth are all over the web BUT they seem, to the beginner, very complicated.

from http://www.engineersedge.com/gear_formula.htm

So I decided to simplify the issue and it works very well at both large scale and small scale. At small scale it works best with machine cutting with laser cutters for example when very small gears can successfully be made this way.

Step 2:

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Step 3: The Easy Way

So how.
1. the shape of the teeth is simplified to be half a circle

Step 4: Working Out the Size of Everything

2.We can now easily sort out some simple maths to make our gear

a. How big/small do we need the gear teeth to be, (diameter) - The smaller the gear the smaller the teeth need to be.
b. All the teeth that are going to mesh, (connect), together must be the same size so calculate your smallest gear first.

3. Lets start with a gear tooth size of 10 mm

I want a gear with 5 teeth on it so the circle will be 10 x 10mm round (circumference)= 100 mm

To draw that circle I need to find the diameter so I use a bit of maths and a calculator a divide the circumference (100 mm) by Pi = 3.142

This gives me a diameter of 31.8mm I can draw this with a compass and then fit exactly 10 circles 10mm diameter round it with my compass.

If your able this is easier to do with even the most basic drawing software. If your using software you should be able to rotate the tooth circle round the main circle and will need to know how far to rotate each tooth - This is easily calculated by 360 deg / the number of circles so for our 10 circles 360/10=36 deg rotation for each tooth.

Step 5: Making the Tooth Shape.

delete the top of one circle and the bottom of the next circle. To make this work out there must be an EVEN number of circles.

4. We have our first gear. This can be cut in wood or metal with basic hand tools, saws and files.

5. It is easy to repeat this process for any number of gears as we need them. Keep the circle size the same and they will fit together.

Step 6: You Have Your Gear

6 Because this semi-circle shaped gear tooth is easy to cut you can do it with hand tools, a sabre (jig) saw or even a coping saw.

In the past I have made a template of 9 or 10 teeth from plywood and use it as a guide for my hand router and cut the gear teeth with little trouble.

If you have access to a laser cutter these can be cut from 3 or 5 mm acrylic and work well down to very tiny sizes.

Step 7: UPDATE

Just to add this to these ideas. Some time ago i tried making simple plywood circles and gluing on the outside a cut down timing belt from a car. This worked as well and is a LOT quicker to do.

You need to select a diameter that will suite the teeth spacing on the belt. I elected to cut between 2 teeth and make my join there.