The Giant Spirograph

What’s eight feet across, has 90 teeth, and makes beautiful designs? Not a shark with an art degree, but this giant version of the classic Spirograph drawing toy. Chalk is the medium, and streets and sidewalks are the canvas.

This oversized art tool features a six-piece outer ring for easy transportability, and three different sized inner gears to vary the patterns you're able to draw. Multiple chalk locations let you customize your designs even further.

This is a relatively simple build, but it requires patience. You'll be cutting out a lot of gear teeth, and it's worth the time to get them right so everything fits well together.

Required tools:

• Jigsaw
• Handheld router
• Hacksaw
• Drill
• 5/16" drill bit
• 1/4" drill bit
• 1-1/2" drill bit
• 1/2" diameter pattern bit for the router, with at least 1" of cutting depth
• Wrenches to fit the nuts listed below

A bandsaw and drill press can make things easier, but they aren't necessary.

Required materials:

• 3/4" plywood (1 sheet)
• 1/2" plywood (1 sheet)
• 3/4" MDF (1/4 sheet, or 2'x4')
• Thick sidewalk chalk (approximately 1" diameter)
• Spray adhesive
• 1.5" swivel casters (3 per inner gear)
• 1/4" carriage bolts, 3/4" long (12 per inner gear)
• 1/4" washers (12 per inner gear)
• 1/4" hex nuts (12 per inner gear)
• 5/16" carriage bolts, 3" long (9 per inner gear)
• 5/16" washers (27 per inner gear)
• 5/16" nuts (27 per inner gear)
• 1" PVC pipe, 6" long
• 1" PVC pipe couplers (qty varies per inner gear — see PDF attachments)

You may not want to build all three inner gears right away, so I've specified the materials per gear instead of total. Multiply anything listed as "per gear" by three to build the complete set as in the plans.

You'll need to print some of the attached files on a large-format printer capable of handling paper 3 feet wide. Your local print shop can help, and it shouldn't be too expensive.

Which files? I've put them into a few different arrangements so you can use whichever ones work best for you.

outer_gear_segment.pdf
This is the pattern for one segment of the outer ring.

22_tooth_gear.pdf
35_tooth_gear.pdf
44_tooth_gear.pdf
With these, each inner gear is contained in its own file. The thick black lines should be cut out. The light blue lines are simply guides, with marks at each inch. The red circles should be drilled (use one of the guide marks as a center) to the same size as your pipe fittings. Bolt holes are marked for drilling to attach the wheel support. If you only want to make one inner gear, use one of these.

44_35_22_gears_nested.pdf
This file has all of the gears nested together. It'll save you a few dollars on printing, but you'll pay for it with the frustration of having to find center and measure and mark all of the holes for wheels and chalk.

wheel_support.pdf
This is simply a six inch circle with locations marked to be drilled for the supporting bolts. Your caster will go in the middle of this circle, but I didn't mark bolt holes for that because the pattern will depend on the specific casters you use. If you don't print spirograph_combined.pdf, you'll need three of these per inner gear. The good news is that it's sized for 8.5x11" paper.

spirograph_combined.pdf
This file has all of the above combined into one 36"x128" file. That's right, 10 feet of paper. You can ignore everything else and print just this.

Each sheet has a 1" square on it to ensure that the files are printed the same size and weren't accidentally scaled by the printer. If the parts aren't the same size, the gears won't mesh. You can either measure the squares or simply hold them against each other in front of a light.

The outer ring consists of six identical segments that fit together like a puzzle. To ease production, we'll make a pattern and use that to guide our router.

With spray adhesive, glue the pattern for the outer ring segment to a piece of MDF. Cut along the lines with your jigsaw, and smooth any rough spots with sandpaper. Drill two mounting holes through the middle of the pattern as marked.

It's a tight fit, but it is possible to get all six segments out of one sheet of plywood. Place the MDF pattern onto your 3/4" plywood, then drill through the mounting holes and through the plywood. Put a bolt through each and hand-tighten the nuts.

Trace the pattern with a pencil, then unbolt and remove the pattern. Cut roughly around the outside of your line with a jigsaw, but don't worry about being too exact because the pattern bit in the router will clean it up.

You could cut the entire thing out with the router bit (it's what you see me doing in the picture), but that puts a lot more pressure on the bit and will wear it out faster. By rough-cutting first with your jigsaw, the bit only has to clean up one edge instead of cutting all the way through.

Reattach the pattern and bolt it down tightly, then follow the perimeter with your pattern bit in the router.

Repeat this six times for a complete ring.

Roughly cut the patterns for the inner gears out of the paper; you don't need to follow the lines exactly at this stage, but only around the outside of the gears.

Lay out all three (or just one, if that's what you want to start with) on the sheet of 1/2" plywood to figure out how to best fit them all on the same sheet, then spray-mount them.

Using your jigsaw, start cutting along the lines of the pattern. Settle in with some good music and find a groove, because this step can be pretty tedious. I found it easier to cut all the way around the outside first, then all of the edges of the teeth, then finally square the bottoms.

To cut the circles that the wheels will pass through, drill a starter hole large enough for your jigsaw blade to fit into, then cut along the line. If you're using the template with the nested gears (it doesn't contain guides for the circles), use a compass to draw three 4" circles equally spaced around the edge of the gear and about 1" in from the innermost edge of the teeth.

The gears ride on swiveling caster wheels that allow them to rotate and roll. We can't attach the casters directly to the gear, because then the inner gear would be riding 2" above the outer gear, without their teeth ever touching. Instead, we'll mount the wheels on a small platform.

Cut three five-and-a-half-inch circles from the same 1/2" plywood you used for the inner gear. Drill three holes in each, evenly spaced around the circle and about 1/2" in from the edge. There's a PDF template for this to make it easier.

Put these circles over the holes on the gear, and drill a corresponding hole in the gear. Be sure to mark which circle goes with which hole, because if they don't have their holes in exactly the same spots, they won't be interchangeable.

Drill holes as needed to match the mounting pattern of your casters and mount one in the center of each circle.

From the bottom of the gear (there isn't really a top or bottom yet, but this step will make one), assemble the wheel mount as follows:

• Insert a 3" carriage bolt through a hole in the gear
• Put on a washer
• Tighten a nut against the washer
• Thread another nut partway onto the bolt, leaving an inch of space between it and the nut below it
• Add another washer
• Repeat for each of the holes
• Drop the mounting circle onto the three bolts, with the caster wheel going through the hole in the gear
• Put on another washer
• Cap it off with a nut

It seems complicated, but take a look at the photo above to better understand it.

You'll need to repeat for each wheel on the gear, and once all three are done you'll need to adjust the nuts up and down on the bolts to get the caster wheel to barely poke out the bottom.

By now you have outer gear segments and you have at least one inner gear; it's time to put them together and see if they mesh!

You may need to adjust the nuts on the wheel mount to get the clearance correct. You want the inner gear to ride high enough off the ground that it doesn't catch on every bump in the road, but low enough that the gears mesh.

You're almost done!

The chalk is held in place by a short piece of PVC pipe inserted into pipe couplers at various locations on the inner gear. Chalk near the edge of the gear will draw a wavier line than chalk near the center of the gear.

Drill holes the same diameter as your pipe couplers at various radii from the center. You can follow the spots marked on the template or choose your own locations.

Cut the pipe couplers in half with a hacksaw, and glue one into each hole. Be sure you mount it the right direction so that your pipe can be inserted from above.

Cut a six inch piece of PVC pipe. Insert it into a pipe coupler, and drop your chalk in. You can experiment with a short piece of dowel on top of the chalk to provide downward pressure (as in the photo above), but I found that the weight of the chalk itself was usually enough.

Repeat the "Inner Gear" steps for each remaining size gear, or start playing with what you already have done.

When all the mechanical work is done, finish the Giant Spirograph however you like, whether painted in bright colors like mine, natural or stained wood, or even patterns. How about using a small Spirograph to decorate the large one?

To use your Giant Spirograph, find a smooth piece of asphalt or concrete and lay out the segments of the outer ring.

Choose an inner gear, drop a piece of sidewalk chalk into one of the holes, and start rolling it around.

Moving a gear around the outer ring is easiest with a team. Each person pulls it around where they can reach, then rolls it along to the next person. The gears have enough mass that they can roll at least halfway around the circle if you really shove. The wheel supports work well as handles to move the gear around the outer ring.

Switch chalk colors and locations, and combine gears to make patterns. You can even roll one of the smaller gears around a larger gear, without using the outer ring at all.

Happy chalking!