Sooyeon Jeong

Computer-Controlled Machining

I made a frame with a headboard for a twin mattress for this week's assignment. I designed the cuts with Inkscape. At first I tried to use FreeCAD since I wanted to see how the 3D structure would look like before cutting the plywood but ended using Inkscape, which I was already comfortable with. The original design had star shapes and text but I removed them because the tool diameter was bigger than what I would have wanted the graphics to look like. Everything was supposed to be press-fitted.

I exported the file into .pdf format and imported it into PartsWorks software in the machine shop computer. Some of the vectors were funky, not imported as closed vector shapes but made each edge of the cut into a small thin rectangle shape. So, I modified them appropriately. I loaded the plywood onto the CNC machine bed, made four clearance holes on the wood and then screwed the material onto the sacrificial board. ShopBot was already turned on when I got to the machine shop so I zeroed the x and y axes using the ShopBot control software, and used Controls>C2 to automatically zeroed the z axis by placing a metal plate below the tool. Tom Lutz helped me a lot during this process. I made T bone shaped fillets on the press-fit slits for the parts. This is to make sure the angled edges would be cut out enough since the tool is shaped circular. For each shape, I made two tabs. I made two toolpathes. Both of them were profile toolpaths but the first one would cut the press-fit slits from inside/left and the second toolpath was cut from outside/right setting. Cut Depth was set to 0.52 in and the actual depth for the material was 0.5 in. Then after turning on the spindle with the key, I started the cutting process and pressed the green button.

However, after cutting the material and trying to assemble the bed frame, I realized that there was an error in the design; the length between two slits on the headboard was too wide. So instead of using the slips to press-fit the parts, I decided to screw the sides of the frame to the headboard and the footboard. In our lab, we had some #8-2 inch screws. The screws went into the material fairly well but when they were inserted to the side of the cut, the wood started cracking. For better assembly, I should have used angled brackets instead.

Finally, the assembled bed frame looked like this. When I put force onto the middle parts where a mattress would go onto, one part was bending significantly than the other parts. I am guessing this was because the slits were cut too widely so there was room for the part to wiggle and bend. If I redo this assignment again, I will have to buy stronger material so that the parts would not bend as much and make the joints stronger by putting angled brackets instead of press-fitting and screwing parts together. Also, I would choose a smoother material for the sleeper to not get splinters from the frame.