Press‐fit car with rotatable wheels

Using the laser cutter, I built a press‐fit car with cardboard. The wheels can rotate though the friction is large. I started with designing a 3D model of the car in Fusion 360. I found online a nice picture of a car and traced the outline in sketch. I extruded the shape in sculpt enviroment and edited the points to create the desired car shape. The 3D model then exported to 123D make to generate slices for laser cutting. For easy assembly later, I added a notch factor of 0.5 to create the chamfer to guide the cardboard. After choosing the number of slice and the slice direction, I export the drawing into illustator to add the wheel structures.

Because the automatic generated drawings can't accomodate moving parts, I added the wheels manually in illustator. The wheel design is inspired by Dan Chen. I cutted a round hole in one of the body slice as the hub. And the eight keys fit through the hub, connecting the wheels together as shown below.

After finishing the designing, I went on to cut the pieces. The first trial didn't quite work because the cardboard is thicker than I designed. As the consequence, it's really hard to fit the joint. I managed to put some pieces together to form a car shape and tested the wheels. So I decided make a new one with bigger slots. Instead of going through the entire process to change the slot dimension (the slicing is parametric but I need to add the wheel struture each time I change the design), I thought it will be much easier to scale the entire design slightly. This is not problem for me as I don't need the car to be a certain size and it fix the fitting problem. So I tried different scaling and found 110% gives a reasonable easy joint fit.

However what I didn't expect is that although a single joint is easy enough to assemble, when I assemble the whole thing one slices need to fit in all slots at once. And the friction makes it so hard to force through. In the end I have to crunch the slices with a plier before I can fit them through.

Another difficulty is that many pieces are very similar to each other and really hard to tell which piece should go where. It took me 4 hours to assemble the car. So the tip for future would be mark the pieces with numbers before take it down from laser cutter and use bigger slots for complicated fits.

For the Vinyl cutting, I cut a small sticker and put it on my phone. The detail the cutter can achieve is quite amazing.