Subtraction Week 6 – CNC Project

March 3, 2016 / By

Planning

 

I had originally planned on making a guitar, I grabbed the plans for a Les Paul from here and set about finding some material. I made a pilgrimage to Rosenzweig lumber in the Bronx on Friday. I asked for Ash, Alder or basswood. I Tried Ash and learned how dense it was. I don’t think I would have been carrying that back on the subway. They had some good pieces of basswood but again, in about 10 foot planks. The only piece they had readily available that day that was wide enough and short enough to carry that I could find was a piece of walnut. “Great”, I thought until the price tag was totted up: $276. I don’t think I was ready to make that commitment on my first time making a guitar.

As a result of this experience I learned what a board foot was and the value of shopping for material with a little foreknowledge. I will probably return to Rosenzweig for the material when I make the guitar in the near future. Unless there is a delivery service that will do a better job.

So, in lieu of the guitar , I made the git-chair.

 

Materials

 

3/4 inch plywood from Home Depot. More plies but worse quality than what we have been using so far in my opinion. Despite some surface imperfections it cut well, however.

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Set-Up

 

I’m a lot quicker with Mastercam now than when we started. The operations were simple, cut out the pieces and pocket the holes in the “headstock” or back of the chair. I cut over the weekend and was worried about taking too much time as the CNC was booked out. In hindsight I could have left some of the finer details in from the original file as shallow pockets. I screwed the plywood down and cut.

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Process

 

I soon ran into this problem which was worrying when it first happened.

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At first I thought it was a problem with the plywood. It was actually a result of trying to cut the leg pieces too close together. There wasn’t enough support for the remaining plywood on the 2nd to last pass or so. I spaced out the legs in my .dwg and that remedied the problem.

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I ended up with this. I thought the back was too small for an adult sized chair so I stretched it out while keeping the base size in illustrator and recut it.

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The pieces were all a bit rough around the edges and I needed to sand the legs down a bit so that they would fit into the pockets on the back of the chair so I took everything to the belt sander.

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I drilled some pilot holes for the screws on the drill press, which I forgot to document, and measured out on both sides. I then glued the legs in with gorilla glue.

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Finished Product

 

Besides a lack of detail, I think the legs are what really let this piece down. They need to be more decorative and have a brace. If I was to add some finish, I would take apart the chair and add some of the detail I stripped away with the laser cutter. The legs would be a total redesign, I would make a simple x shaped brace and then attach them to that, most likely with screws as they need to be load bearing. I’ll see how well the chair holds up to someone sitting on it in the morning, though.

Having said all that, I do feel wiser for having done this project. I learned properly about the capabilities of the belt sander and I now feel reasonably confident in taking on the CNC guitar project: with realistic expectations for how long it will take. Probably about a 2-3 hour job for the body including pockets and another sub 2 hour job for the neck and bridge. Having said that, The stock will probably be about 2 inches thick so it might even take longer. One for a quiet day at ITP most likely.

 

 

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