![[IMG_20171228_022043.jpg]] # Introduction In my senior year of high school, I experimented with making laser-cut leather coffee cup sleeves for a friend: | ![[cup_1.jpg]] | ![[cup_2.jpg]] | ![[cup_3.jpg]] | ![[cup_4.jpg]] | | -------------- | -------------- | -------------- | -------------- | I never ended up making a proper, final version of this. The year after, I befriended Ella; she loved coffee, and I wanted to make her something similar. However, she's strictly vegan, so leather wasn't an option. # Version 1 ## Initial designs I had already outlined a coffee cup sleeve, traced it in illustrator, and printed it out to ensure it fit. I just put my previous website's logo on it for the sake of testing. ![[cup_5.png]] For Ella, I came up with a couple designs: one that was a favorite quote, and one that was a screenshot from our texts that was an inside joke. | ![[cup_design_1.png]] | ![[cup_design_2.png]] | | --------------------- | --------------------- | ## Deciding on a material In lieu of leather, I went in search of alternatives: prioritizing insulation and a solid feel. After getting some leather from a dedicated leather shop, to compare the alternatives to, I browsed a few craft stores. Several kinds of cloth felt flimsy and didn't have the solid feel that I'd wanted. Pleather comes recommended, but it's made of PVC which emits cyanide gas in a laser cutter; it didn't feel solid enough anyways. I decided that wood was the only alternative which would give me that luxurious, well-built feeling that I valued from the leather version, so I decided to use my favorite material: 1/8" Birch Plywood. Balsa was a valid alternative: it may have been more conducive to bending and could be made stronger with several protective coats of finish. <figure> <img src="Website/Media/Cup/cup_7.jpeg" alt="Initial sleeve designs"> <figcaption>Birch plywood (above) and balsa wood (below).</figcaption> </figure> I cut these out with my favorite machine from the UWB Makerspace: the ULS 1' x 2' laser cutter. ![[cup_6.jpeg]] ## Approaching wood bending > [!Warning] Note: I did this project in pretty much one day > I was fixated and in a bit of a rush, so I couldn't invest too much time into this. From whatever I could find on the internet, I had a couple options: 1. Steam bending 2. Ammonia bending I didn't have the time, money, nor resources for the latter; and I didn't have time to make a proper steam rig for the former. I knew I could boil the wood, but the plywood still wouldn't bend that easily. I felt out of options, and I needed to figure out something else. I shuffled between home, UW Bothell, and Canyon Park Junior High several times - getting advice from Tod Mass (my former woodshop and engineering teacher) and Ivan Owen (who ran the UWB Co-Motion Makerspace). Mr. Mass mentioned living laser-cut hinges, as I'd done before for a previous project; but this wasn't an option because I wouldn't be able to engrave a design on the surface. Another suggestion he made was kerf cuts on the back. I didn't have access to a tablesaw for this, but, I did have a desktop CNC machine at the UWB makerspace. Mr. Owen approved of the idea and taught me how to use the machine. I drew kerf cuts on the sleeve outline, then utilized the scrap material from my previous cut as a rig to hold the already laser-cut wood in-place during milling. I experimented with several different depths of kerfs and eventually narrowed it down to a very specific measurement: the depth which would just barely reach the last ply, such that the last ply could bend like thick paper. | ![[cup_8.jpg]] | ![[cup_9.jpg]] | ![[cup_10.jpg]] | ![[cup_11.jpeg]] | | -------------- | -------------- | --------------- | ---------------- | > [!info] Fun fact > I named the CNC machine and am quite proud of what I'd picked out. When I got home, I soaked this in boiling water and bent it around a cup with relative ease. After this little victory, I decided to forgo experimenting with balsa wood. ## Bending the designs Design 2 went rather well: | ![[cup_12.jpg]] | ![[cup_13.jpg]] | | --------------- | --------------- | However, Design 1 didn't: | ![[cup_14.jpg]] | ![[cup_15.jpg]] | | --------------- | --------------- | | | | | | | ![[cup_16.jpeg]] > [!question] > Why did Design 1 break where Design 2 didn't? I will acknowledge I got a bit impatient when noticing cracks while bending Design 1, however, they would have formed regardless of how long I took. Obviously, thicker pieces of wood are stronger than thinner pieces of wood, meanwhile, thinner pieces of wood are more flexible and easier to bend than thicker pieces of wood, i.e. have smaller chances of cracking. The conclusion I'd reached was that the overall thickness seldom matters past a certain threshold. The cause of the cracks was not due to an incorrect overall thickness, but rather, the sharper differences in thickness throughout the single piece of wood - specifically those caused by the deeper, vector laser engravings. As seen in the first two images below, the cracks only occurred where the vector laser engraving was cut deeper than the rest of the design. The last image shows how the shallower, lighter part of the raster laser engraving had no cracks. | ![[cup_17.jpg]] | ![[cup_18.jpg]] | ![[cup_19.jpg]] | | --------------- | --------------- | --------------- | | | | | Another way that I'd interpreted this is that the modulus of elasticity varied across the material - with thinner regions bending significantly more than thicker regions given the same applied force; the sections with large differences in moduli of elasticity is where the fractures occurred. I continued with Design 2: glued the ends together, clamped it around the cup, and let it sit overnight. ![[cup_20.jpeg]] ## Finishing up this version The day after, I tested applying 2-3 coats of mineral oil to the broken piece to give the final product some protection and a glossy/ transparent finish. It turned out as expected, so I applied it to the final design. A few days after, I gave the coffee cup sleeve to her and she seemed happy with the result! I also ended up realizing that because of the kerf cuts, the sleeve provided excellent insulation - much more effectively than the cardboard standard; and it likely insulated better than one made of leather. # Version 2 | ![[IMG_20171228_022043.jpg]] | ![[IMG_20171228_001909.jpg]] | | ---------------------------- | ---------------------------- | | ![[IMG_20171227_174615.jpg]] | ![[IMG_20171227_174637.jpg]] | ![[IMG_20171228_003107.jpg]] | | ---------------------------- | ---------------------------- | ---------------------------- | I made these over a year after, and here are the steps I followed: 1. Come up with a design using the template with Illustrator (or an equivalent software), w/ proper RGB values for rastering and cutting. Make sure the engraving is as shallow as can be while still being visible; no vector cuts unless they're evenly cut along the horizontal length of the sleeve. 2. Engrave and cut the design on 1/8th inch birch plywood. *It is much easier if the grain aligns vertically* (so that it bends far more easily). Otherwise, if you want a bit of a challenge and make a rustic, driftwood look that's *significantly* harder to bend (needs to be kerf cut much deeper and bent more carefully; risks splinters), then you can have the grain align horizontally. You can see the difference here: ![[IMG_20171228_100118.jpg]] 3. Use a CNC machine to make kerf cuts; cut just enough so that the last ply is exposed. I'd highly recommend testing this out on scrap before doing it on the engraved piece since you have to be incredibly precise here, and I seldom trust the reported tolerances of any machine. 4. Boil water; get a flat dish wide enough to fit the wood, a heat-proof pad, heat-proof gloves, a stick, and have your solid cup with clamps nearby. 5. Pour the water in the dish and thoroughly soak the wood. 6. While it's still hot (but not boiling), use your hands to gently massage the wood into shape - bending it over and over again, little by little, until eventually (with enough time and heat and soaking) the desired shape/ flexibility is reached. Time is necessary for the wood to become flexible enough; you may need to keep the water hot. If you've been massaging for an hour with no good results, the wood is too thick or you're not pushing hard enough. After you've started massaging, you can start bending slightly more aggressively: bend until you feel like it might start cracking if you were to push more, but err on the side of patience; a crack cannot be fixed. 7. Remove and dry it with some towels. 8. Clamp the sleeve onto the wood - relax for a couple minutes - then unclamp, apply glue, and clamp again. 9. Make sure to wipe off any excess glue - this is difficult to fix later. And then you're done! Apply mineral oil or leave it for a more rustic driftwood look.