# Week 6: CNC Milling - Making Something Big <a href="../index.html">Back to Home</a> This week we were given a 96" x 48" piece of OSB, a plywood alternative that has a reputation for splintering, and access to the ShopBot CNC router, a machine with a reputation for imprecision, to construct "something big" through CNC joinery techniques. One key difference in using a CNC router vs a lasercutter is that the former can't cut sharp inside corners, necessitating T-bone or dogbone slots so that the drill bit (1/4" in diameter) can make the turn while still allowing the piece to be slotted in completely to the end of the slot. Files for download: * <a href="files/vivzhong_layout_twosides_whole_final.dxf">File for milling pieces to construct White Tree of Gondor</a> ## Initial Design I've always wanted to make something aesthetic and beautiful, and this week I finally had the chance: a coat hanger in the shape of a tree. I started out by looking for inspiration among Google results for "tree coat hanger", but then realized that I was forgetting one of the best trees of them all: the White Tree of Gondor. I found a high-res image (thanks Reddit) and converted the PNG to SVG and then to PDF with CloudConvert in order to import it into Rhino; the program conveniently imported the image as a closed curve. <img src="images/tree_image.jpg"/> For stability, I wanted to have four sides to the tree. Inititally, I wanted to take the easy way out and just duplicate the tree, cut slits down the middle of the trunk, and then assemble by slotting one tree down through the other. But there wasn't enough room on the board, so I then deconstructed each side into the root, trunk, and branch sections that would fit together like jigsaw, with four-way connectors incorporating dogbones around the jigsaw connection points. <img src="images/foursides_layout.jpg"/> Assembled: <img src="images/foursides_assembled.jpg"/> ## Changes After TA Review I sent my design to Zach, got the following feedback and made changes accordingly: | Feedback | Change | | | | |------------------------------------------------------------------------|------------------------------------------------------------------------------------------------|---|---|---| | So many branches would take too long to cut on the ShopBot | I limited the four sides to two sides, save for the roots of which I needed four for stability | | | | | The dogbones are too close together; the piece would have fallen apart | I moved the dogbones such that there was at least 1" between the cutouts. | | | | | The sharp corners would all be imprecisely cut on the ShopBot | I made liberal use of the Fillet tool to smooth any inside angles | | | | I then realized that the dogbones' radius were smaller than the drill bit, so I changed the dogbones into T-bones. Evolution of the connector pieces: <img src="images/connector_evolution.jpg"/> Final layout of pieces: <img src="images/twosides_layout.jpg"/> Final note: This week marked my discovery of something I really should have found earlier: use of the Orient tool. Thank Eru for the Orient tool. ## Cutting Before cutting, we had to upload the design to VCarve and calculate the toolpath, adding tabs to keep the pieces in place as the maching cut them out. We then had to go around the board and drill screws through the board into the ShopBot bed to secure it. Alas, the board was apparently very bowed, so the machine drill bit went too deep, ploughing through the entire board in one pass instead of two. This meant that the tabs didn't really happen, which meant the pieces were not secured. Luckily Zach noticed it early on, and saved my pieces by adding screws as the ShopBot cut them out. <img src="images/zach_savior.jpeg"/> When I tried to assemble it hastily, I realized that I should have put slits in the tree itself so that the connectors would keep the pieces together even without a perfect fit. Not sure why I didn't think to do it until it was too late. <img src="images/hastily_constructed_tree.jpeg"/> I'll come back later to sand and probably glue.