Aztec Calendar was my first experience making wooden gears and they turned
out rather well. I became interested in making things with moving pieces.
I have several projects planned that involve gears in different configurations
and various moving parts. So I began experimenting with different gears and
mechanisms for future use in these projects. One of the things that I wanted to
experiment with was a homemade "chain drive" system -- a way to transfer power from one
axle to another parallel axle. Below are some of my trials and errors and some
I decided to use short sections of dowel that were connected by string. In my first
attempt I cut sections of dowel that were 2" in length. I drilled a tiny hole
through the dowel at 1/4" from each end. I drilled these holes at my drill press
using a special jig made to
hold cylindrical objects. The jig has sides that are sloped at a 45-degree angle
to hold these round objects steady while drilling.
These gears were slightly different than the ones I had made before. The first time
I cut gears I used a band saw to cut out the teeth from the edge of the circle.
This time I chose to make gears by adding the teeth rather than cutting them out.
I started with two circles that were 3" in diameter. Each circle was 1 & 1/2"
thick (two pieces of 3/4" plywood glued together). Then I held each gear in a clamp
on my drill press as I drilled holes into the edge. Each hole would then be fitted
with a 3/8" dowel that extended from the edge of the circle by about 1". When
finished, these gears looked like the old Tinker Toys I used to play with as a kid -- a
circle with a peg protruding from the edges along a radius every 45-degrees. These
8 radii would be the "teeth" that would drive the chain.
To prevent having to tie off each dowel, I decided to use small beads as spacers in between
each dowel. This would ensure the correct spacing and also might add some visual
interest while the chain is in motion. When I purchased the small beads at the
craft store, I also purchased some clear plastic cord that is used to string the beads.
My first version of this chain drive utilized this plastic cord. Unfortunately,
this plastic cord tends to stretch just a little when enough force is applied. When
the first chain was placed around the two gears and turned, I noticed that the plastic
started to stretch in certain places. This chain worked for a while, but eventually
the stretching cord caused the dowels to be spaced improperly and the chain no longer
meshed smoothly with the gears.
In my second attempt I decided to use 8 lb test fishing line in stead of the plastic cord.
That would be stronger and would not stretch. Again I chose to use beads as
spacers, although this time I used different colors. I also shortened each dowel
segment -- from 2" down to 1 & 1/2". I wanted them to fit a little more tightly
around the gear teeth.
These changes seemed to help somewhat. First of all, the fishing line was much
stronger and, of course, did not stretch at all. Second, the dowels were now the
same width as the gears which looks more appropriate. However, the chain still has a
tendency to come off the gears as I'm turning it. It might help if the gear teeth
were a little longer. Also, the beads, while excellent as spacers and ensuring the
correct distance between the dowels, sometimes tend to bind a little while going around
the gear. Perhaps these gears simply have too small a diameter for them.
Larger gears would cause the chain to turn at an angle that was not so sharp and
that might be easier on the chain. My next attempt will involve slightly
larger gears and dowels that have no beads as spacers -- just fishing line tied off around
each dowel segment.
The rack that I used to run this chain drive on is just a rectangular frame of 1 & 1/2" x
1 & 1/2" wood screwed together at the corners. I cut dadoes in the underside so that
I can stand the frame on two pieces of plywood and change the height as necessary.
The four pieces the hold the 1/2" axles are just scrap plywood with 1/2" holes
drilled through them. These are just clamped in place. That way I can slide
the axles closer together or farther apart to install the chain and then to vary the
tension on the chain once it's in place. The whole assembly breaks down quickly
and easily for storage.