Growing projects one dimension at a time

What do Ikea, Captain EO, and CNC router tables have in common? They all use 2D materials to make 3D things and it’s easy for you to do, too. (even without any of those things)

Mini Rocket

Mini Half-Lap Rocket

There are a TON of things that people use every day made from flat materials… tables, cookie sheets, bookshelves, wooden Santa Clause puzzle kits, picture frames, and even this MDF rocket. Sure factories use automated power saws, die cutters, and tools that cost more than your house, but that’s only because those tools are required by manufacturers to keep their costs per item down. If you only have to make one of something, your technique doesn’t have to be so sophisticated. Even CNC machines and 3D printers can be overkill. The only tools you’ll need for some DIY projects are a sturdy work surface, a saw, and a drill.

There are many ways to use sheet material to make structures and they all use some combination of opposing forces to make the structure strong. One of the most common (and my favorite) is to use columns between plates to expand the flat dimension of your material. This does two things: First, it makes even a flexible plate more rigid (stronger) the same way an I-beam gets its strength from three relatively thin plates (in engineering terms, this increases the moment of inertia without increasing the weight). Secondly, it adds a lot of volume to what you are making without adding much weight. On a large scale, you could use PVC pipe, a few washers, threaded rod, and some nuts to make the columns. The opposing compression in the pipe and tension in the threaded rod make the column super strong, stable, and rigid.

Arduino with Standoffs

Standoffs are a perfect example of column-separated plates

Another joinery technique is actually the subject of this project day: the half-lap rocket. The idea here is to cut opposing grooves in material so they fit together like a puzzle. When the two pieces are joined together, the structure will be very strong because a force that would bend an unsupported thin plate in half is being opposed by the other plate not wanting to bend along its edge.

One of my favorite projects lately has been some small MDF rockets made out of two cutouts in 1/8″ thick material. The outline of each one is identical and the only difference is that one piece has a slot from the top to the middle and the other has a matching slot from the bottom to the middle. When you put the two pieces together, the rocket is free-standing and 3-dimensional. The best part is, you can make the same figure with some MDF and a coping saw, just follow these simple steps!

1) Draw the object you are going to cut out. Feel free to make anything you like. The guiding principle for the rockets was to make them symmetric with the half-laps made on the dividing line. If you want to use my design to make a rocket ship, print this PDF.

2) Cut out the shapes. Make sure the cutouts are as clean as possible. They will become a stencil in the next step.

3) Trace the stencils onto your material. Remember, the slots won’t work unless the material and the slots are both about 1/8in thick. If your material is a different size, adjust the slot width to match. Make sure to leave some room around the tracings so your cuts in the next steps won’t start right next to the finished cutout.

4) Use a coping saw to cut between the two tracings and cut away most of the excess material. The idea is not to start cutting on the lines of the tracings, but rather to leave room so your cuts aren’t starting right next to the cutout in the next steps.

5) Using a drill, drill a 1/8″ hole at the end of each of the two slots, this will make it easier to finish them. If you don’t have a drill available, you can use a back and forth method to clear the material from the end of the slot in step 7.

6) Make your detailed cuts by cutting lines from the edges of your material to the sharp inside corners. Remember, coping saws can cut contours just fine, but it won’t cut hard angles easily and could even break your blade. Make multiple cuts to take the excess material away in wedges or strips.

7) Now that the exterior of the tracing is gone, cut the grooves. If you have a piece of thick scrap with a straight edge, you can clamp it to your cutout with the edge right on the line of the groove so as you cut, it will make sure the blade doesn’t go too far astray if you lose your line.

8) With the two halves of the rockets done, you can sand the edges smooth, put them together with a little glue in between, and you’re done!

If you’d like to add some finishing touches, you can paint them with a crazy design or add some LEDs for a more retro high-tech effect.

Bonus project!


Coping Saw Guide made from 1/8″ aluminum bar

I find its best to use a cutting guide to improve the precision of my cuts and make life easier in general. You can make one with a long strip of scrap. Thick, rigid material is best. Mine is made from a scrap of aluminum plate. Cut a V in one end of the scrap at about a 60 degree angle and secure the other end to your work bench. As you cut, if you keep the saw blade close to the crook in the V, there will be more support on the material, so more of your energy will go into cutting and less into keeping the material flat on the edge of your bench, allowing you to control the direction of your cuts.

Using the techniques here, you can make a LOT of things from mini animals to project enclosures. The possibilities are as limitless as your imagination.

That was my project day, how was yours?

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One thought on “Growing projects one dimension at a time

  1. Pingback: The ThrAxis – A Scratch-Built CNC Mill | It's Project Day!

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