Wood Joinery with Techno CNC

Last time I was lucky enough, and/or the CAD/CAM job was really neatly done. Outcome: the wooden container came out to be a beautiful piece with finished details.

This time the techno CNC sorcery won, I could not make a seamless wooden joint after a several attempts. As always I worked on the assignment on weekend when the shop is usually empty. I did some sketching first with paper and pen, looked at the reference examples on Subtraction class page, and then made vectorworks drawings:


I tried Oval-shoulder halving and Tenon halving with ellipse and rounded square shaped window. For the oval shoulder I tried two different drawings: One with zero tolerance and other with a 0.01″. The pieces with zero tolerance needed a lot of sanding, and the ones with 0.01″ tolerance were somewhat simpler to assemble.

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It required considerable efforts on sanding the surface areas and hammering the pieces to fit them together, but this could have been a lot better and easier with more tolerance.

I ran into and learned a lot from two issues-
1. Stupid mistake I did in CAM: I made a significant mistake in the parts that had oval and rounded square windows. In setting contour and engraving orders, I had put the engraving first, then outside contour for the whole piece, and then the contour for window inside the piece. As a result the piece was not stable when the oval window was being cut. I had to pause the router and fix the piece into the spoilboard with two screws so that it wouldn’t wobble. The oval window got completely spoiled though, but I was able to manage it in time for the square window.
2. Bad quality of the material: The ply had an uneven, kind of burnt layer underneath the oval window piece. The layer got chipped off as engraving reached a certain depth.

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