Wednesday night's workshop demonstrated how to use bike parts to make a spirograph drawing machine. The instructables' site we chose to base the workshop from is here. I was able to make a few improvements to the design, which also cut the making time down.
Here it is:
Step 1: The tools, parts and pieces.
*compass or sting attached to a pencil
*double sided tape
*scrap 1/4" plywood
*scrap 1/4" plywood
*hammer and point driver (or a chain breaker)
*WD-40 (to clean the chain and gears)
*drill and drill bits
*scroll saw (could use saber-saw)
*Hot glue gun + sticks
*recycled bike chain
*recycled bike gears
*scrap pieces of wood about 1/8" thick
Step 2: Prepare the chain
Using the hammer and point driver (or chain breaker) release the pin from the joint in the chain. Once you've done this you can add or shorten the chain, making the circumference of the chain your desired length, thus the size of your drawing can be customized.
Step 3: Find the circumference and plot onto plywood.
I simply laid out the chain in the most accurate circle I could get by "eyeing" it. Then I took my ruler and found the largest measurement for the diameter. Using the compass, I plotted the radius (center point) of the circle. At this point, I make the compass a hair smaller than the outermost circumference measurement. This way, you can sand the circle to the perfect size (you can always take more off, but you cannot add wood back on).
Step 4: Drill and cut on scroll saw.
Using a large drill bit (larger than 1/4"), drill a hole on the inside of the circle close to the edge. Take your wood to the scroll saw and cut along the inside of your line. (Note: if you are cutting a large circle out of your plywood, you may be able to save those scraps to make a smaller spirograph with a smaller chain.)
Step 5: Sand circumference to size and glue
Using an oscillating sander, sand the circumference to where the
chain will fit tightly within the circle. (Note: be careful, because it is easy to take too much off.) Once fitted, use the hot glue gun to glue the outer edge of the chain to the inside of your plywood cutout. (Note: also, be careful not to let the hot glue seep into the gaps of the chain, or else the gear will bump into the glue messing up your lines). Don't use too much glue, but enough to make it hold well.
Step 6: Preparing the gears.
The graphs you can generate will depend on the number of teeth in your chainring and the number of links in your chain. If you think of the graph as a star, the number of points in the star will be the lowest common multiple of the tooth number and link number divided by the tooth number. The number of times you have to trace around is the lowest common multiple divided by the link number.
Here are some examples off the instructable's post:
130:52 -> 5 points (5x52 = 260 = 130x2)
130:48 -> 65 points (65x48 = 3120 = 130x24)
84:52 -> 21 points (21x52 = 1092 = 84x12)
84:48 -> 7 points (7x48 = 336 = 84x4)
I didn't really pay attention to this, but I had a number of gears to switch out with in case they were proportional and wouldn't skip beats.
In the instrucable's post, they used the gear just as it was. This led to gooey residue getting on the page and choppy transitions in the line when the pencil got close to the chain, thus making it come loose from its path. To problem solve this, I cut out a small disc of wood that did not interfere with the gears (just smaller than the circumference of the gear). Make sure the disc of wood is no thicker than an 1/8". Because this elevates the gear, the pressure of your pencil (when close to the circumference of the circle), does not make your gear come loose from the chain. Also, this prevents the metal of the gear from scraping your paper with the gook that it picks up from the chain. Another advantage to this addition is that you can customize your marker/pencil holes. Simply drill holes into the exposed wood using different sizes for different marking utensils, and in various places. This makes one gear have a number of options for one drawing.
To attach the disc of wood to your gear, simply use double sided tape between the two, then use a clamp to apply pressure, therefore there will be a strong hold. Then you're ready to drill.
Step 7: The good stuff!
Clamp your chain template on top of your paper on a table (or I prefer to just have a friend hold it down). Enjoy making cool drawings and colorful designs!
You can play around with the shape of your circumference to make unique shapes too!
Hope you all had fun, and feel like you learned something!