Techno Router: Making a wooden container on CNC

Of all the machines we’ve learned so far in Subtraction class, techno router is the one I enjoyed the most. It felt like using a scaled up Othermill router where bed size has been enlarged considerably from 5.5 X 4.5 inches to 8 X 4 feet. Also this assignment involved the most hacks and impromptu workarounds than other machines.

I thought of complex ideas initially, such as making a simple chair or stool with a few joints, but soon dropped that idea as making drawings in vectorworks for the first time was really tricky. I then decided to make a cylindrical wooden container with a lid, and made a few sketches:

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As shown in the drawings, I wanted to make stackable ring layers that would form the walls of container, with interlocking protrusions and cavities. However I dropped that idea as the size and shape of the mill bit was another complex parameter in designing the joints. Finally I made digital drawings of flat rings that could be stacked and glued on top of each other to form a cylinder.

For some reason the MasterCAM always threw an error when I tried to apply contour operation to more than one objects, “The selected sub-chain does not touch the branch point.” I googled the error and most of the blogs mentioned some fixes in vectorworks which I did not understand. As a solution I tried making a similar drawing with .dwg extension in Adobe Illustrator, and it fixed the error. I was able to apply all the contour and pocket operations. (Using illustrator triggered another problem later!)

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Three circles from the column on the left are the bottom (solid circle) and two lids (I planned to make two, just in case), with some engraving on the rim so that it would snap on the opening of cylinder. I set three operations:

  1. Cut the inside circles from the rings (Contour, counter-clockwise)
  2. Engrave rims of the lids (Pockets)
  3. Cut all circles and rings from outside (Contour, clockwise).

Next I prepared the techno router with a plank fixed to the bed. I required a 2’6″ x 1’6″, but found a slightly bigger sheet of plywood.

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Next I set the origin and preprocessed the GCode file,

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…And then something weird happened on hitting fire. The router head further advanced in -Y direction and started cutting a circle:

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I immediately hit the pause button, thanks to Ben’s instructions. The reason was I was working in bottom-right quadrant in the MasterCAM software, and I had completely forgotten to take care of it when I shifted from Vectorworks to Illustrator! This is evident from the blue MasterCAM image shown above. I thought of possible solutions andcould think of two:

  1. Go back to MasterCAM, move the drawing to top-right quadrant, export GCode and start all over again.
  2. Put the sheet in bottom-right quadrant. That is, set the Zero a couple feet away in +Y direction, and start the operation from beginning. The drawing would still be cut in bottom-right quadrant.

I decided to go ahead with the second option as it was quicker. I stopped the current file, moved the head approx 3 feet in +Y direction, and selected Zero All. This worked perfectly well, with drawing set in +X and -Y directions. Next part involved patience, vacuuming, and monitoring the router operation:

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The ply had a few underneath cavities and therefore a few rings were not perfect. Good I cut a few extra:

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Next I applied glue and stacked the rings one by one on top of the bottom piece, and applied clamps to hold everything together for about an hour:

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The cylinder looked beautiful and I sanded it evenly on the belt sander tool in the shop. This part involved careful handling as the cylinder was a bit slippery on the sander, because it was rolling like a wheel as soon as it touched the sander belt. The next trick was sanding it from inside. I used one of the circular pieces cut out from within the rings, glued sandpaper to its rim, and mounted it on drill machine. This custom-sander was really effective in finishing the inside surface of cylinder:

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I used the same tool to sand the lid. The sanding made the lid a little smaller in dimension, and allowed it to snap perfectly on top of the cylinder:

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Here’s how the final product looks:

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