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John Bump
5,717 followers -
Mad scientist
Mad scientist

5,717 followers
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Subaru is in the shop for a failed head gasket, so I drove the Spitfire to work. It did fine on the 100 km/h sections, even. I was cruising along and saw a guy coming towards me in a beautiful mint-green 1968 E-type Jag. I waved at him. He hadn't managed to get past looking shocked at the sight of the Spitfire before he was past. Yeah, sure, your car is worth $200,000 more than mine, but we're both driving Little British Cars in a sea of monster trucks and SUV's, pal.
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People had asked about the casting porosity I'm getting in my 3d print to cast aluminum experiments. Here's what happens when I run a flycutter across one of the castings. I'll put it under a microscope later tonight, but this already looks good enough (once I finish machining the surface flat) to be oil- or water-tight against a gasket. Stuff like this is hard to fixture securely enough to surface in a single pass!
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Another round of casting. This time I didn't seal it with wax, just cast around the raw printed PLA, and it worked fine. (You can see surface features reflecting the print infill structure in the resulting casting.) The plaster of paris worked fine, with a longer burnout using a slower heat increase. My dimensional error (measured vs. intended, as a result of aluminum significantly shrinking as it cools) is now 0.2%, although the range of measurements runs from 1.5% to -2%. I have to think about that some more. But, I have generally worked the bugs out and can move to casting usable parts.
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7/31/18
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Today I tried some variations on the aluminum casting theme, and got a perfectly acceptable casting. Printed PLA, coated with wax. This time I ramped the burnout oven up in three steps, hoping the more gentle thermal shock wouldn't crack the mold. It cracked anyway. But the second thing I tried worked well: I reassembled the cracked mold pieces and put the whole works (hot) into a dry sand/clay mix, to hold it in place, and then put some steel plate on top to prevent the aluminum floating the top of the mold off. I think I'm about at the end of the road for using plaster of paris. It's too delicate. But the rest of the system seems to be working quite well. This plate is the carburetor end of an intake manifold, to bolt to a SU side draft carburetor, and has allowed me to characterize my casting process to determine how much the aluminum shrinks in cooling. When I do stuff that has to bolt up to an engine, I need to expand the original print enough so that the resulting casting comes out the right size. This is the first time I've cast something with holes in it. They came out perfectly. The weird line across the whole casting is where the upper 30% of the mold cracked and I reassembled it: a thin flashing of aluminum leaked into the crack. The joggle on the face is 0.5mm thick, which is well within the tolerance I need for machining this flat, so if this were the right size, it would be a usable casting.
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7/22/18
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Video of player add-on for standard piano, Dougherty Museum, Longmont. This is the most marvelous thing I've seen in a long time.
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Video of player piano with drums and tambourine, Dougherty Museum, Longmont
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Video of platter-type music box, playing a punched steel record. Dougherty Museum, Longmont.
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About 200 tons of old steam-powered farm equipment, including the first John Deere and Case products and steam tractors the size of small buildings. I'd never seen transverse engines in tractors before. (It seems like a really silly design, wasteful of space.)
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7/15/18
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Cadillacs, Rolls-Royces, and other amazing 1920's finery, Dougherty Museum, Longmont.
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7/15/18
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Stanley Automotive Works steam-powered 9 passenger touring car, plus a 25 horsepower Stanley steam engine, Dougherty Museum, Longmont.
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7/15/18
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