How to Make Wooden Gears

Wooden gears and sprockets have been in use for millennia. While the history of early gears is somewhat unclear, they were first written about by the Greek mathematician Hero of Alexandria in 50 AD. However, there is evidence that the Greeks used them in the third century BC, when Archimedes invented them. Other evidence points to the Chinese as the inventors, who may have used gears in chariots centuries before. Of course, like many ancient inventions, neither precludes the other, as many inventions came about in different places at different times. Due to the lack of reliable communications and commercialization, inventions didn’t spread as rapidly as they do today.

While some of those early gears may have been made of metal, there were also a lot of gears made of wood. One of the more prolific uses of wood gears was with water wheels. We usually only see the wheel itself, but the wheel rotates around an axle (a whole tree trunk), that goes into the lower room of the mill, where it is run through a right-angle gear drive, and possibly other gears to increase the speed, allowing the power developed to be sent upstairs into the working area of the mill.

Many early clocks used wood gears, too, although few examples remain today. The constant wear on the wood demonstrated the need to switch to metal gears, which provided more accuracy and durability.

Today, wood gears are more of a novelty than anything else. Woodworkers make wood gears more for decorative purposes than anything else. That doesn’t mean they have to be limited to that use, though, as they can be pretty helpful for those who make their own jigs and power tools. There are many ways that wood gears can be used for making that tooling, such as in moving a sliding table. It all depends on the woodworker’s imagination.

Many people who make these gears cheat a bit, just like the companies who manufacture wood gears for sale. By “cheat,” I’m referring to making them via laser cutting. While that works well and produces clean gears efficiently, it takes something enjoyable and challenging out of the process. Making wood gears isn’t just getting the finished gears and enjoying the road from here to there.

Let’s Talk Gears

There’s a fair amount of misunderstanding about gears that we should probably clear before making any gears. First, “gear” and “sprocket” are often used interchangeably, even though they aren’t the same thing. The fundamental difference is that gears mesh with other gears, while sprockets are designed to be used with chains or toothed belts.

The second thing we need to understand is that for any set of gears to work, all the teeth of the gear must be the same size and shape. It doesn’t matter if we’re talking about spur gears, internal gears, helical gears, or bevel gears. In each case, the teeth on every gear used in the set must match.

One exception is when two gears are mounted on the same shaft and turn together. In that case, one gear can be toothed to work with one set, and the other can have a different size and/or type of tooth to work with another set. This is quite common, especially when using gears and sprockets together.

The other exception with wood gears is something specific to water wheels. The water wheel’s axle often has a crown wheel attached to the other end. This is a round wheel, with dowels sticking out around the perimeter, much like candles on a birthday cake. These “teeth” on the crown wheel interface with a lantern pinion, a barrel-shaped device with wheels on either end, connected by a series of dowels. The crown wheel and lantern pinion are used mainly because they don’t require high precision. When mounted, the lantern pinion sits so that the spokes of the crown wheel go between its dowels, so that as the water wheel turns, the force developed is sent at 90 degrees up through the floor of the mill.

In the case of wood gears, we can’t make the teeth too small, as they lose strength. I’m unsure if anyone knows the bottom end of tooth size, but it would depend, at least in part, on the material used. If a circle were fabricated out of sections of maple so that there was end-grain sticking out all around the circle’s perimeter, it would have the strength to cut smaller teeth, but for most applications, it is best not to go smaller than 10mm.

Material selection is essential—the need for all the teeth to be firm limits the manufacture of wood gears to some plywood. But not just any plywood will work. Softwood construction plywood has too coarse a grain with too many voids to make gears. Using something with a fine wood grain and no voids is much better.

How Gears are Used

Gears can do three basic things: change the speed of rotation, change how much force is transmitted, and change the direction of rotation. Changing the direction of rotation doesn’t impact the other two, but changing either the speed or the direction affects the amount of available force.

First, the number of teeth on the two gears affects the output speed. If there is a significant input gear with a small output gear, the speed will increase, as each revolution of the input gear will equal several revolutions of the utput gear. In contrast, if a small input gear is used with a large output gear, it will take several revolutions of the input gear to equal one revolution of the output gear, slowing the speed. Count the number of teeth in each gear and use that as a ratio to calculate precisely how much of a difference.

That ratio will also allow for calculating how the change in speed affects the change in available force. If the ratio is 10:1, meaning that an input speed of 10 gives an output speed of 1 (ten times as many teeth on the input gear as on the output gear), the force provided will be 10 times the input force.

This is commonly used with gear motors. It involves taking a motor’s natural speed, which is either 1800 RPM or 3600 RPM for an AC motor, and reducing it to what is needed. For example, reducing 1800 RPM to 180 RPM will allow a 1/10 HP motor to do work that would otherwise require a 1 HP motor at 1800 RPM.

It All Starts with the Design

The number of teeth each gear has and not the size of the gear is the starting point for the design of any gear train. In some cases, the size of the teeth is determined by the need to shoehorn the gear into a specific amount of space, but that’s assuming the luxury of working with hardened steel gears, which can carry much more load than wood gears can. Still, the idea fits, as wood gears that need to take a lot of load would need to either be made of thicker plywood (perhaps laminating several sheets together or made larger to have more prominent teeth (or a combination of the two).

For our sake we’re going to assume ½” gear tooth size, as that’s a common, easily available size that just about any woodworker will have in their kit. If we need a gear with 10 teeth in it, we need to calculate based on 20 teeth, as the space between them needs to be the same size as the teeth. So, 20 times 0.5” gives us a circumference around the circle of 10”. To find out what diameter that is, we divide the 10” by Pi, Π, which is 3.14, and we get 3.18”. So we must draw a circle with a 3.18” diameter or a 1.59” radius.

After drawing that circle with a compass or on the computer, we need to draw our 20 – ½” circles around the circle so that each touches its neighbor. Let’s step through this process:

If using a compass:

1. Start by drawing two lines, perpendicular to each other, in the center of a piece of paper (best to use cover stock). 
2. Sharpen the compass’s lead and set the compass to 1.59”
3. Place the compass point at the intersection of the two lines and scribe a circle around them. 
4. Reset the compass to 0.25” (this might require a relatively small compass)
5. Pick a point on the circle’s circumference and set the compass point. Then, scribe a circle around that point. 
6. Move the compass so that the lead of the compass is at the intersection of the large circle and the small one that has just been drawn. Then set the compass point on the 3.18” circle, wherever it naturally falls. 
7. Scribe another ½” circle. 
8. Continue around the circle this way until the 20^th circle meets back up with the edge of the first. 

If using a computer:

1. Open any vector drawing program and make two perpendicular lines on a blank page.
2. Make a 3.18” diameter circle, centered on those perpendicular lines.
3. Since we need 20 ½” diameter circles, we’ll divide 360 degrees by 20 to get 18 degrees. 
4. Make a series of lines, each with one end on the center of the crosshairs and the other end rotated 18 degrees and offset from its neighbor. Most vector drawing programs allow you to type the value in, providing the exact placement of those lines. 
5. Make a ½” diameter circle. 
6. Move that circle to its center at the intersection of the 3.18” diameter circle and any lines radiating from it. 
7. Copy the ½” circle and move the copy to center it on another intersection. 
8. Continue this way until all 20 of the circles have been drawn. 
9. Print out the drawing, preferably on cover stock.

The diagram above was made in an older version of Corel Draw, following the above directions. I have also created an almost identical diagram in AutoSketch to prove it can be done. The diagram below removes all the extra lines, making it easier to see how the gear will look when cut out.

This sort of gear will work well when used on the flat, along with other gears, to increase or reduce speed. However, round teeth like this are not the best design when the gears are perpendicular to each other, as this would be needed to change the direction of the movement.

An excellent tool for designing gears is available online. All that’s needed is to insert the number of teeth in each gear, tooth spacing, and a few other pieces of information. The application makes the design real time, allowing you to print a full-sized pattern. This app is available at WoodGears.

Making the Simplest Form of Wooden Gear

There are ways to cheat to get good wood gear without having to go through all the trouble of cutting out all the teeth. While this is not really something that any of us would want to do for decorative gears, it can be useful for shop equipment.

The secret is to use a serpentine belt designed for use with a sprocket. These belts have ribs running across the width rather than ridges running down their length. The ribs work rather well as gear teeth in applications where there isn’t a lot of load on the gear. Proper spacing of the gears is necessary so that the teeth make good contact without crushing the rubber and causing excessive drag on the gear train.

Cut the belt to provide the correct number of teeth to make this gear. Ensure they have complete teeth and a whole valley at one end. Measure how long this section of belt is and divide that by Pi to determine the diameter of the wood disc needed to mount it.

Draw a circle with the correct diameter directly onto the plywood used to make the gear. Be sure to mark the center well also. Then cut the circle out, cutting it slightly large. Drill out the center and put a matching-sized pin through a scrap piece of plywood to act as a sanding jig to help ensure that the finished circle is exactly the right size. This piece of plywood must be clamped to the belt sander table with the gear blank set on it. Turn the gear blank around, sanding all sides. Then, readjust the jig, moving it slightly closer. Keep moving it in, step by step, trimming off a little bit more, all the way around, until the disk is the right size.

To finish the gear, the belt must be glued t the outside of the plywood disk, teeth out. Contact cement would be best for this as it adheres well to wood and rubber. Use an ample amount on the plywood, as it will tend to soak into the end grain of the inner plywood.

Making a Wooden Toothed Gear

Making the pattern is the most challenging part of making any wood gear. Once that is done, it’s just a matter of drilling and cutting to get the desired gear. If cover stock is available, I’d recommend printing the pattern on it rather than on ordinary printer paper. The heavier cover stock is less likely to become damaged when used, even though it would still be destroyed if cut.

Start by gluing the pattern to the piece of plywood used to make the gear. I recommend using rubber cement for this. Gears can be of any thickness, but wooden gears of the type we are making are typically between ½” and ¾” thick. Rough-cut the outer dimension of the gear.

If the pattern is cut out, the outline and all the pertinent points can be traced as an alternative to gluing it to the wood. This eliminates the worry about the pattern tearing right be cutting out the gear.

Mark all the locations to be drilled using an automatic center punch, a scribe, or a scratch awl. If we compare the first diagram with all the guidelines with the second one, it’s clear that every other circle is drilled out, making the spaces between the teeth. The circles that represent the teeth themselves are not drilled out. Mark the center as well, as that will need a hole drilled.

Please note that accuracy is paramount. One trick that can help those who have trouble getting the exact center when trying to use the above-mentioned tools for marking the center of a hole is to chuck up a finishing nail in a cordless drill and then sharpen the nail with a grinder, making it needle-sharp. The needle-sharp point makes it easier to locate the exact crosshairs, and the drill will allow that modified nail to drill an indentation into the wood.

Double-check the hole locations, making sure that none of the teeth were marked accidentally. Then, drill a small pilot hole (1/8”) through the gear in all of the locations. Use a sacrificial backing board while drilling to help prevent blowout.

Replace the drill bit with a ½” drill bit or whatever size the gear teeth are. Drill the hole out again, forming the space between the gear teeth. Unless a brad point drill is used, this may need to be done in stages. Drill out the center hole for the axle as well.

The rest of the teeth must be cut out on the band saw. However, the table should be tilted five degrees to provide clearance for the gears to mesh together if the gears are used in a right-angle configuration. Cut only the right side of each slot and then tilt the table five degrees to the other side so that both sides of the teeth will be beveled equally. If the table doesn’t tilt in the other direction (many don’t), then clamp a piece of plywood to the table with a spacer underneath the right side to create a five-degree tilt in the other direction.

With the teeth cut in both directions, go back around the outside of the gear, cutting the teeth off to length. Smooth the teeth with a file, then sand the entire thing.

Cutting the Teeth on a Router

It is also possible to cut the teeth on a router table. To do so, a simple sled for the gear blank to ride upon and two pieces of wood clamped to the router table to act as fences are necessary. The overall shape of this is trapezoidal, with the angle of the fences and the sides of the sled matching the angle needed for the sides of the gear teeth. The sum of the space between the sled and the two fences controls the size of the teeth.

Once this jig is set up, the fence is slid along one of the fences to cut one side of the gap between teeth and then slid along the other fence to cut the other side of that gap. A block clamped to the back of the router table can help ensure that the router bit doesn’t cut too deep.