How to Cut Spur Gears

One of the greatest discoveries in mechanical action has been the gear. It links together two more more separate axles to transmit power. By changing the ratio of teeth between two gears, you can adjust both the speed of rotation and the strength. Gears are present in countless devices and mechanisms, from your CD-ROM drive, to your car's transmission, to your kitchen can opener.

The most common of gears, and the one most would picture, is the spur gear. This gear features the teeth on the outside of the wheel, just like those in a watch or similar mechanism. Depending on the material you are making your gear out of, there are a number of techniques to cut a spur gear. A few of these will be described here, with the assumption that the reader knows how to use the machines that are mentioned.

Things You'll Need

• Material for your gear (Paper, wood, steel, aluminum, brass, etc.)
• Cutting tools (scissors, saw, milling machine, etc.)
• Marking tools (pencil, pen, scriber)

Instructions

1. Make a paper gear. This is the easiest way to make gears, and is useful for paper and cardboard automaton and devices such as paper clocks. The process involved is to have an outline of the gear drawn or printed twice, once for each side. These will have the teeth in place, along with an extra paper border of tabs along the teeth. After the two faces are cut out, these tabs are folded in, providing a place for a third, long and thin piece of paper to wrap around the outline of the teeth. Being secured with glue, this forms the depth dimension to the gears.

2. Make a wooden gear. These gears have been used in a number of devices and mechanisms for many years, before they got replaced with their metal counterparts. There are two styles to wooden gears. The first style is one where, like the paper gears, the teeth are cut with the wheel. An outline is drawn and the gear cut out with a saw. The other kind has removable teeth, useful when breakage occurs. The wheel has holes cut around its periphery, and the teeth are inserted and wedged in place.

3. Make a metal gear by outline. Metal gears are the standard, with steel being used in automobiles and brass and bronze in your analog pocket watch. The first method to machining gears in metals is to repeat the process described for wooden gears. Once an outline is traced and scribed into the material. The bulk of the material is cut away with a saw, and the final work done with files and jeweler's saws.

4. Make a metal gear by milling. Milling a gear involves the use of a milling cutter, similar to a drill bit, but whose shape matches that of space in between two teeth. Once the metal wheel is secured to the milling machine table via an index stand, the cutter is used to mill one gap between two teeth. The gear is then rotated the distance between two teeth, and the cut is repeated. This cycle continues until the gear is made.

5. Make a metal gear by hobbing. A much simpler way to make a gear with a milling machine is to hob the gear. A hob is similar to a screw, except that the twist has the profile of the gap between teeth and that it is interrupted in many places, providing a cutting edge. To hob a gear, the blank wheel is mounted on a stand which can freely rotate. Some wheels have small starter cuts made in a similar way as above. The wheel is then advanced into the spinning hob, which will not only cut the gaps between teeth, but whose twist will also spin the gear in order to cut the entire circumference.

Tips & Warnings

• There are countless methods for cutting gears, and numerous books on the subject. Stay educated. Take your time and exercise careful setup and patient cuts. Once a cut is made, it cannot be undone.

• Even when making paper gears, exercise caution when using cutting tools. Machine tools are very powerful tools for cutting and shaping metals. Just remember, you are softer than metal.