Joint Experiment

Our second CNC assignment is to create a wooden joint. We needed to mill the wood carefully so the result provides a solid connection between the two pieces.

I designed and milled a Blind finger tenon joint. I am pleased with the final result:

Two pieces of 0.5 inch wood. One has two small protrusions and the other has two identically sized and shaped holes.

Two pieces of 0.5 inch wood joined together. The wood with the protrusions is inserted into the one with the holes. The view is from the side.

Two pieces of 0.5 inch wood joined together. The wood with the protrusions is inserted into the one with the holes. The view is from the top.

The most difficult part of this assignment was designing the joint in Vectorworks with the proper tolerances. The tolerances were guesses for how much wiggle room I should incorporate into my design. In the end I guessed 0.01 inches. It proved to be a very good guess.

I created the G-code on the CAM machine and fired up the CNC.

wood rectangle screwed down to CNC bed, also made of wood. The CNC's drill bit hovers above the wood.

After milling the first few pockets I paused the job and added two screws to keep my pieces in place. After the contours are cut the pieces would otherwise not be connected to anything and would be free to fly around the room.

wood rectangle with holes cut into it, and hole with screw in it.

I resumed the job and cut the contours.

CNC cutting into rectangle piece of wood

After a few minutes the contours are cut. Now, the big question: how well do the two pieces fit?

wood rectangle with two pieces cut out of it, with both pieces screwed down.

I found that the fit was pretty good. The finger tenons extended a little bit through the finger holes but not significantly so.

Two pieces of 0.5 inch wood joined together. The protrusions of one fit into the hole of the other, but in this case the protrusions are a bit too long and they extend out the bottom a bit.

Two pieces of 0.5 inch wood joined together. The protrusions of one fit into the hole of the other, but since this is the top view, you can't tell.

I wanted to try and see if I could get an even better fit. I went back to my laptop to model a slightly different piece in Vectorworks. Then I moved the model to the CAM station:

computer screen with design of shapes on it, showing where the CNC will cut.

And back to the CNC computer:

CNC computer screen with job loaded and buttons to stop or start the job.

The second and last piece was quickly milled. When it finished I found it fit the perfectly.

I am going to use the results of this experiment in my midterm project for this class. My goal is to make a towel rack for my bathroom because I hate the one I have. This project sounds simple and perhaps that not exciting but there is a lot of detail to focus on and learn from. I'm interested in the project and I'm excited to work on it.

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