One of the great things about 3D printing is you can print multiple parts that are printed interlocked in their proper spots so they come off the printer already assembled!
This past October, I tried my hand at "moving parts" to make a “Dial-O-Lantern” toy for my kids. The concept was a 3D printed Jack-O-Lantern with three sliding pieces that would allow you to “dial” and configure between 3 different sets of eyes, 3 sets of noses, and 3 sets of mouths-- a total of 27 different face combinations. The pumpkin printed completely assembled and has a removable lid so an LED light can be placed inside.
I modeled my pumpkin in Blender, which is free and open source. Since I do not own a 3D printer of my own, I had my pumpkin printed by Shapeways in their Strong & Flexible Plastics, the color orange of course! : )
In this Instructables article, I’ll go over the thought process behind some of my design decisions and then my modeling approach in Blender. Attached at the end is the final .STL file of my pumpkin which you can print for yourself. If you don’t have a printer or your printer isn’t capable of interlocking parts, you can also order one to be printed by Shapeways.
This model is licensed Creative Commons (With Attribution and No Commercial Use Without Permission)
With every 3D printing project I take on, I have found the crucial first step is to decide on my materials and familiarize myself with the material requirements. I knew right off the bat that I wanted to print in the Strong & Flexible Plastics from Shapeways. I hit up the material’s design requirements. I was specifically interested in the clearance between the separate parts. My pumpkin was going to be three separate pieces. I needed to know how close those pieces could be without getting fused together. In this case, I needed to make sure my parts were 0.5mm apart.
Now that I knew how far apart all the pieces needed to be, I had a trickier question. How to connect and make the three pieces of the pumpkin slide together? I did a lot of sketching and brainstorming on paper and I went through many revisions of ideas, some exceedingly complex. Sometimes it pays off to get an outside pair of eyes! A brainstorming session with my husband produced a nice simplified concept. I went with a tongue and groove approach. It would be similar to how Pergo flooring connects together, only in a sphere. The top and the bottom pieces would form grooves and the middle piece would have tongues that would fit inside.
Using the minimum clearances and settling on a minimum wall thickness of 1 mm, I had an idea of how large my connections were going to be.
Believe it or not, the connection sizes dictated the size of the final pumpkin. Anywhere there were connection rails, I wouldn’t be able to cut out any of the facial features. I didn’t want to end up with a pumpkin where the eyes were oddly spaced from the nose. I wanted to make sure the distance between facial features appeared right. Once I knew how much “uncarvable” space I was going to have on all my pieces, I made some mock cylinders in Blender the same height and then I experimented with some dummy triangles to get a feel for how big a pumpkin I would need for the proportions to look right.