This is a toy that looks complicated and seems like it demands real precision to work at all but honestly, it's pretty straight forward and there is a bit of wiggle room in the measurements. (Wiggle... caterpillar... never mind.)
The toy came together over several weekends of trial and error. Hubris and the occasional flying disk o' death off of the miter saw delayed me but I'm fairly confident that one of these could be made (but maybe not painted) in a day without too much grief.
So to begin at the beginning...
A few years ago I made my first caterpillar automata. Ultimately, I called it "The Very Hungry Caterpillar That Photographed Very Poorly." It was a gift for one of my nieces and it is still working today.
I didn't have a set of plans for that one. It was just a proof of concept that became a finished toy. That was the same approach I took with this one; build and test as I went along.
I needed to make a toy for little one's school auction and for a friend's newborn. I wanted to try my hand with some more automata and I recently came across Woody Mammoth's version of a caterpillar toy on the web. I really liked the look of his, so it seemed like the way to go.
So... for those following along at home; here is Cam Terminology 101:
Now on to the build.
I used a pine dowel for these. One batch seemed to have rougher edges that splintered a bit but a lot of factors can go into that. They cleaned up fine.
The front and back pieces were 3" tall. They have a 9/32" hole right through their very center and need to line up since the rod need to go through both holes.
Once the holes were done I glued one end to the front of the top and the other to the back of the bottom to make two "L" shaped pieces. I put a coat of beeswax and mineral oil on them but was careful not to get any on the surfaces that will need glue during final assembly.
So then there is some test fitting to see where that locking disk needs to be placed to have the followers line up with the cams. By having the bases of the followers be a little less that 1/2" wide and the cams exactly 1/2" wide, it makes it run pretty smoothly. I hit a few of the "feet" of the followers on the beltsander once or twice just to give a little more room. Once I was happy with the alignment, I glued the locking disk in place and the top and the bottom together.
Now the the body...
I purchased a 1 1/4" diameter poplar dowel from the local old school hardware store. I used it for the 7 main body segments. I also cut one disk each from a 1 1/8" and a 1" dowel for segments toward the tail. Each segment needs to be just short of 1/2" thick. The poplar dowel splintered a lot less than the same sized pine dowel I used for the cams and had a smoother,denser end grain after it was cut and sanded.
Benjamin Forstner) to get a nice flat bottomed hole. I made the holes 3/8" deep. You could probably make this with 3/16 dowels but I find the birch dowels I get in that size to be pretty fragile. Your millage may vary.
The smart thing to do now is to test your body segments to make sure they don't rub against each other too much AND THEN paint and finish them even though they will be slightly thicker once painted. Just be sure to keep the segments in the same order you test fitted them. 1/16" one way of the other really makes a difference. You don't want too much wiggle room between the pieces though since it can allow the followers to get out of alignment and interfere with each other. Don't let this stress you out. It's a toy. Not the engine on an airplane. It will work fine.
Okay then.. all set.
The full critter
And here he is in action. I did the cams slightly different on this one with an extended cam in the tail (not needed) and a longer cam for the head that worked as the locking piece as well.
My guess is that most parents of the last 40 or so years are familiar with Eric Carle's "The Very Hungry Caterpillar." It's a great book and it has a very distinctive style. I could never match it but I figured I could capture the vibe by using some of the same colors and shapes.
People really like the pleasant wiggle and whimsical nature of this toy. It really has whet my appetite for simple automata. Stay tuned.