Computer Controlled Machining

Design

For this assignment we have been given a 48x96 inch (7/16 inch thick) sheet of strand board. The only requirements for this assignment are to make something big. Our machinerary of choice is the Shaper Origin at the International Design Center (IDC). But I am also interested in using the ShopBot 3-axis CNC router to do some cool maps designs, if there is time.

So my original thought was to make some sort of plant stand, specificially for my fabulous aloe vera plant that is slightly too big to sit on my window anymore. I found a few interesting ideas online, but they all seemed rather plain.

Then I thought I should examine what kind of patterns I could put on such a planter. I found a really nice idea from April Johnson's design where she used a Voronoi pattern. I decided this would be a great challenge! I also wanted to make sure that the sides could be connected with box joints. You can see my initial pattern here.

Voronoi

In math, a Voronoi diagram is a way to split up and partition a plane according to the distance of points in a subset. The subset or partitions are referred to as Voronoi cells and they make really nice patterns.

I found someone's existing open-source code under the GNU GPL v3 (code) . But I would have to agument it a bit to fit the parameters of the cutter.

The first attempts looked really nice though! I have been using OpenSCAD for almost all of my 3D modeling

Joint Design (and hacking)

I decided to use joints for the frame base of the plant stand, and then use wood glue to put the top in place. The sides of the table have box joints modified to work with CNC. Because CNC routers cannot cut sharp corners I added a "dog-bone" joint with little circles at the corner. Since I am using OpenSCAD, which has no idea what points are, I added my own circles at the edge of the slots. This page has a nice description of all kinds of joints.

I initially wanted to have the top also connected with joints, but I thought this might be too difficult.

I did have to change the joints a bit. I misunderstood the "dog-bone" design and placed the circles too far away from joint. Since the milling machine can't make close corners, we add a small circle to the joints. The circle radius should be the bit size, so that my radius was the bit size over 2. The dimensions of the bases were a height of 30 inches, and a width of 12 inches (to match the plant stand that I have at home). The top was 12.5 inches, so there would be a little bit of extra material on the top.

Milling

Since my design was rather complicated, and consisted of a lot of intricate cuts, I used the CNC machine in the basement of IDC. This machine has a vacuum so that the board does not have to be drilled in place. I had to remove a few of the Voronoi cut outs because they were too small and the drill bit would not be able to cut them. I also had to make the cut-outs smaller so that there was a couple inches between the border and the design. Zach helped with this.

We had to stop the mill a couple minutes in because the drill bit caught onto one of the design cut-outs. In order to eliminate this in the future, we went back to the design and had the mill only cut partially the way through. This leaves a onion skin behind that can be stripped off later (although that ended up being quite a pain).

Sanding and Preparation

Removing the onion skin layer was a lot of work! I had a LOT of hekp, since we had to punch out all the cutouts (which was fine), but then we had to sand the inside with a file. Finally, we sanded the front and back sides with a round sander and prepared to put the pieces together.

Putting it all Together

To my surprise, most of the joints held up great! We used a few clamps to make sure that everything lined up correctly. I also ended up gluing two of the sides together so that I could transport it easily. I also glued the top on.

The Finale

My large aloe vera plant is very happy to have a new home!