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Very interesting. I've been trying to find a way to go sleek lights without cutting any metal away, but I'm getting tired of looking at options. I think this might be a better route, at least for the time being. I'm excited to see how this pans out. Good work!
Well my first foray into urethane casting has had its ups and its downs. Its a lot more work than I thought it would be, and getting a perfect part is a lot harder than expected. It also takes a lot longer to cast a part than I had hoped - currently it takes me almost 45 minutes to setup, mix, pour and clean up. That means 3 hours per set of headlights, not to mention the modification of the Sonar housings. I have ideas on how to speed this up, but I sure do miss just hitting "start" on the 3D printer and walking away. I wish the printed parts lived up to my expectations of strength and surface finish.
The first two castings came out pretty good, but I am having some air entrapment issues.
Then with the third attempt disaster struck. I created Venom...
I thought maybe my cheapo digital scale had malfunctioned and I had screwed up the mix ratio. So I picked up a mechanical lab balance and a set of calibration weights at a local auction. Turns out the cheapo digital scale is actually pretty damn accurate (+/- 1 g or about 0.7% of the part weight). So the only explanation for the black goo is that I must have forgotten to heed the warning on the Side B jug that says "Shake well before EACH use". They aren't kidding - this stuff separates within hours.
Casting #4 turned out almost perfect. Thoroughly shaking the B side resulted in the fastest cure yet. I also was able to relieve the major bubbles by putting the entire mold in the vac chamber after pouring, and pulling medium vacuum on it to help the material flow in.
Casting #5 turned out like crap, even though I did almost exactly the same process as #4. I think I pulled too much vacuum on the entire mold and it ended up creating more bubbles than ever before so the part has big voids in it. So the trial and error continues. I am going to get a smaller vacuum chamber so I can reach full vacuum quicker when degassing the urethane. You only have 5-6 minutes working time once you start to mix, and currently my 3 gallon chamber takes ~90-120 seconds to reach full vacuum, which means I can't let it degass for very long before I need to pull it out and pour.
03-01-19, 04:24 PM
