computer-controlled machining
This is the "make something big" week. Everybody gets one 4'x8'x7/16" sheet of OSB and then makes something big with it. My shop section has access to a ShopBot CNC Router and a Shaper. The ShopBot is 2.5 axis cnc router, meaning that it can move in the x-y plane and has some z-axis movement, but it can't go up and down while doing x-y plane cuts. Functionally, the ShopBot has capabilities that are analogous to a laser cutter. The Shaper is a hand held routing tool that's very cool. You lay down a patterned tape on your cutting surface, which the Shaper uses to locate itself, and it guides you through the motion of cutting your piece, where you handle the rough the shapes and it handles the detailing.
I ended up using neither of these machines haha (though I'd like to use the Shaper sometime after this week). The EECS shop section this week was in the IDC (International Design Center, building N51) so we had more limited shop hours. When I went in to cut, the power was out to the shop. But! there is a bigger, fancier CNC router (Onsrud) in that building that was working, and I got to cut on that. The Onsrud has a vacuum bed, automatic tool head changes, and all sorts of other functionality that I'm not fully aware of yet. The CAM tool that was used with it was MasterCAM, which a nice guy at the shop helped set up for me. If I'd been using the shopbot, I probably would've used VCarve, which from watching other people use seems reasonably intuitive? And apparently for the Shaper, Fusion360 does a good job of generating the tool paths.
I didn't know what I really wanted to cut (I'd CAD-ed a chair, but its features were probably too delicate to be structural, and I'd also CAD-ed a pseudo-rocking chair, but it seemed large and impractical), so I ended up making a coffee table for one of the lounges in my dorm because the table we have is ~struggling~. I messed up the sizing for one set of legs on the table, so those just got left out of the construction. The lesson there is to always pre-assemble your parts in the CAD environment. I got lazy and decided that I only needed a 2D drawing and now I have a gently wobbly table. Oh well.
I used Fusion360 to draw the parts, but I did the layout/minor edits in AutoCAD.
The table is more or less a press-fit construction. An important consideration for using a CNC router is that the tool diameter (in this case 1/4") is a significant size, and that parts coming loose off the cutting bed can both be hazardous and design-ruining. With the ShopBot, the stock is held in place by wood screws going directly into a sacrificial bed layer. When people were cutting on the ShopBot, they also tended to have to pause the cut, drill a mostly cut part into place, and then continue going (in a addition to adding tabs in VCarve, the cam software). Since I used the Onsrud, this was unnecessary because it has a vacuum bed. It was still necessary to account for tool width in making the press fit joints. Functionally, this looks like adding point geometry to any inset/outset tab where a non-rounded edge matters. The machine then drills those holes out, which leaves kind of a dog bone shape.
I added in 2 1x3 blocks to stabilize my table, and now it supports at least 1 person sitting/standing on it, so I think it's good? I also added one layer of satin finish polyurethane to the top, and some white stripes. Maybe I'll paint in the top different colors at some point? (but probably not lol). If I get a chance to, I'll get some better stock and cut out my other designs with the Shaper, too.
