I believe I come into the CNC unit with a unique perspective on the subtractive manufacturing technique. I have extensive experience with CNC mills in the OEDK machine shop, fabricating aluminum and steel parts for Rice Eclipse. However, the vast majority of these parts use the CNC functionality of the mill as more of convivence, rather than out of necessity. That is, the CNC would be used to make a symmetric ring of bolt holes automatically, rather than drilling each one manually, jogging over to individual x and y coordinates. Eclipse has been dipping its toe into more complex geometries that necessitate the use of a CNC mill (or CNC lathe) such as the complex geometry of the diverging portion of a rocket nozzle, or an intricate restraining plate for our rocket engine test stand, but these are far and few between. I personally also skipped over the wood CNC “step” that most people take and went right into metal – which means I’m virtually clueless about the intricacies of wood milling, such as types of mill tips, techniques to reduce damage to the part, etc.

For this homework assignment, I started by picking an image from The Noun Project website. I opted for a space shuttle outline, as I’m a big fan of the space shuttle and just really liked the design that I stumbled upon on the site. I also knew I wanted this design to be smaller and intricate – I wanted to challenge myself to use the smaller endmills that I don’t see much of in metalworking. I also wanted to give at least one copy of the wood piece to my girlfriend, who is a huge space nerd and loves the space shuttle. I wanted to make the design small so she could put it on her nightstand.

Once the design was picked out, I launched into learning and experimentation. I started by picking out some material. I started with some 0.75” thick plywood, thinking a thick material would be good for carving into. However, upon closer inspection, I noticed that the thick plies were already starting to delaminate, which didn’t seem conducive to a good part. I instead moved to two thinner pieces of plywood, totaling around ½” thick with 1/8” plies. I knew the initial cut on the Carvey would be 1/8” thick, so I figured taking off one full layer would be best for appearance.

Once starting the CNC process, I was shocked at how simple the Easel interface was. It was extremely simple to import an SVG and plan cuts around it. I was able to get right into putting my pieces.

My first cut on the chosen plywood was with a 1/6” fishtail up-cut bit; my design was small enough so that I couldn’t use the standard 1/8” bits. While the design turned out well, it was pretty rough around the edges. At first, I thought this was due to the material, as I wasn’t sure plywood was the best choice for this application. As such, I moved to a piece of fine MDF with a similar thickness. This piece turned out much cleaner but still had small splinters sticking it. It was at this point that I decided to move to a down-cut bit – I did some googling and found that the down-cut bits were made to solve the exact problems I was having. Following this advice, I switched to a down cut bit and cut again on the MDF. It was much, much cleaner, but had some small irregularities in the lines. It seemed that the down-cut bit needed a slightly larger pocket in order to make the same size cuts as the up-cut. It was also at this point I noticed some of the smaller features of my piece on my MDF pieces were close to breaking off. The small fin portions and even the small shapes on the wings were wobbly when touched, due most likely to the reduced strength of the small sections of MDF. So, for my final two pieces, I took in all of these lessons learned. I went back to the 0.5” plywood, scaled up the design, and used a 1/16” down-cut bit. This combination produced my final pieces.

       

Overall, the cuts were pretty clean. The only issue was some small edges and corners chipping off, but due to time constraints, I couldn’t afford to start over on both parts. I sanded up both parts to clean things up and then cut the surrounding wood to make both parts roughly the same size. I then coated both parts with a semi-transparent white stain to give a subtle white color (like the actual shuttles) while still preserving the wood texture. I may try to add more detail in the form of black detailed lines in the grooves of the wood to make it look even more like the real-life space shuttle. Overall, time constraints with other classes as well as working on the chess piece midterm project prevented me from putting lots of time and effort into these CNC pieces, but I feel that I still produced a good result that is pleasing to look at. I’d be happy to give this to my girlfriend as a small gift sometime in the future.

Costs:
– Labor: 5 hours at $12/hr = $60.00
– Machine Cost: 2 hours at $25/hr = $50.00
– Wood (stock from OEDK): ~$10
– Stain: $10 for 1 quart = ~$0.50
– Auxiliary materials: rags, popsicle sticks, etc. = ~$1
Total cost: $121.50