Rotem Abeles - How to make (almost) everything – Fall 2013

WEEK 5 – CNC

This week’s task was to build something big using CNC.

I wanted to build a table and a chair for my daughter to use at home. I took measurements and found that the chair should be around 8” X 10” X 13” with another 8-10” for the back support.

I didn’t want to glow it or use any irreversible method, so I designed T-shapes pegs to hold the pieces together, and I wanted to build the chair using plywood.

Following my successful experience with last week Tinkercad, I used it again. However, in this case it was pretty annoying since Tinkercad workbench is only 10”X10” and has a very limited zoom-out range.

The good thing with Tinkercad is that it had pre-set letters, which gave me the idea of making the parts from my daughter’s name – Maya.

Tinkercad can export to .stl and .svg, but partworks cannot read either of them. I tried using 123D CNC utility, which can export toolpaths directly, but that wasn’t customable enough and I didn’t feel comfortable to use it as is on the machine.

Joelle was kind to convert my .stl file to .ai on her Adobe illustrator, which partworks can process.

When I got to the shopbot I found that we had only OSB plates, which is really unsuitable for kids’ furniture, but I decided to use it anyway for a proof of concept.

I learned the importance of thoughtfully placing tabs the hard way, as some of my T-shaped joints were sucked in by the shopbot vacuum!

I didn’t change my design for the different thickness of the OSB (0.4375”) compared the plywood (0.5”) using the difference as tolerance for my joints. This proved right, and I was able to build a (relatively) solid chair, which I could disassemble and take home.

The next day I volunteered to help unload the new boards, with an intention to rebuild the chair with plywood. After examining the boards I decided to go with MDF, which seemed a stronger material and was not too heavy due to the small size of the chair.

I implemented the lesson from the OSB experience and strategically placed tabs on all pieces, and I also increased the spread between parts on the board.

I noticed that the machine cuts MDF in a very clean manner, leaving the dust inside the cuts (making it very easy to clean afterwards).

MDF proved a very good fit for this job, both in finish and in strength. However, the OSB was much more forgiving to my lack of dog-bones, and the same parts in MDF just didn’t fit.

After a couple of hours of sanding and finishing, especially manually adding dog-bones, the pieces were able to connect.

I was very happy with the outcome, and so was the client J

Looking ahead, when I’ll have some spare time, I’ll try building my 2” foam design, which doesn’t use T-shape connectors.