Retrotechtacular: The Master Hands Of The Early Automotive Industry

When motion pictures came along as a major medium in the 1920s or so, it didn’t take long for corporations to recognize their power and start producing promotional pieces. A lot of them are of the “march of progress” genre, featuring swarms of workers happy in their labors and creating the future with their bare hands. If we’re being honest, a lot of it is hard to watch, but “Master Hands,” which shows the creation of cars in the 1930s, is somehow more palatable, mostly because it’s mercifully free of the flowery narration that usually accompanies such flicks.

“Master Hands” was produced in 1936 and focuses on the incredibly labor-intensive process of turning out cars, which appear to be the Chevrolet Master Deluxe, likely the 1937 model year thanks to its independent front suspension. The film is set at General Motors’ Flint Assembly plant in Flint, Michigan, and shows the entire manufacturing process from start to finish. And by start, we mean start; the film begins with the meticulous work of master toolmakers creating the dies and molds needed for forging and casting every part of the car. The mold makers and foundrymen come next, lighting their massive furnaces and packing the countless sand molds needed for casting parts. Gigantic presses stamp out everything from wheels to frame rails to body panels, before everything comes together at the end of the line in a delicate ballet of steel and men.

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Making A Concrete Sign

While paging through the feed a few days ago our attention was caught by something a little away from the ordinary in Hackaday terms, a DIY video about creating cast concrete signage from [Proper DIY] which we’ve placed below the break. A deceptively easy-looking mould-making process has a few tricks that  will make the difference between a hard-wearing sign that lasts for years, and a lump of concrete.

So, to make a cast concrete sign, you throw together a mould with some letters, and chuck in some concrete? Not so fast, because the key appears to be preparation, and ensuring that there are no 90-degree corners on the mould parts. The letters are carefully shaped and sealed with varnish before being attached to the mould with silicone adhesive, and all the corners are beveled. Finally a light oil is used as a release agent, and hefty vibration takes care of any air bubbles.

The result is a set of signs, but we can see these techniques finding uses outside signage. For example, how about casting using a 3D printed mould?

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Nuke Your Own Uranium Glass Castings In The Microwave

Fair warning: if you’re going to try to mold uranium glass in a microwave kiln, you might want to not later use the oven for preparing food. Just a thought.

A little spicy…

Granted, uranium glass isn’t as dangerous as it might sound. Especially considering its creepy green glow, which almost seems to be somehow self-powered. The uranium glass used by [gigabecquerel] for this project is only about 1% U3O8, and isn’t really that radioactive. But radioactive or not, melting glass inside a microwave can be problematic, and appropriate precautions should be taken. This would include making the raw material for the project, called frit, which was accomplished by smacking a few bits of uranium glass with a hammer. We’d recommend a respirator and some good ventilation for this step.

The powdered uranium glass then goes into a graphite-coated plaster mold, which was made from a silicone mold, which in turn came from a 3D print. The charged mold then goes into a microwave kiln, which is essentially an insulating chamber that contains a silicon carbide crucible inside a standard microwave oven. Although it seems like [gigabecquerel] used a commercially available kiln, we recently saw a DIY metal-melting microwave forge that would probably do the trick.

The actual casting process is pretty simple — it’s really just ten minutes in the microwave on high until the frit gets hot enough to liquefy and flow into the mold. The results were pretty good; the glass medallion picked up the detail in the mold, but also the crack that developed in the plaster. [gigabecquerel] thinks that a mold milled from solid graphite would work better, but he doesn’t have the facilities for that. If anyone tries this out, we’d love to hear about it.

1000 Aluminium Cans Cast Into A Guitar

Aluminium cans are all around us, and are one of readily recyclable. While you can turn them into more cans, [Burls Art] had other ideas. Instead, he turned roughly 1000 cans into a custom aluminium guitar.

Both the body and neck of the electric guitar are made out of aluminium. It’s an impressive effort, as manufacturing a usable neck requires care to end up with something actually playable when you’re done with it.

Producing the guitar started with a big propane furnace to melt all the cans down so they could be cast into parts for the guitar. 38 lbs of cans went into the project, and were first dried out before being placed into the furnace for safety reasons. Aluminium cans aren’t made of the best alloy for casting, but you can use them in a pinch. The cans were first melted down and formed into ingots to be later used for producing the neck and body.

[Burls Art] then built sand casting molds for his parts with a material called Petrobond. Wood plugs were used to form the sand into the desired shape. The neck casting came out remarkably well, and was finished with a grinder, hacksaw, and sandpaper to get it to the right shape and install the frets. The body proved more difficult, with its multiple cavities, but it came together after a second attempt at casting.

Fully kitted out with pickups and hardware, the finished product looks great, and weighs 12.3 pounds. It sounds remarkably like a regular electric guitar, too. It does pick up fingerprints easily, and does have some voids in the casting, but overall, it’s a solid effort for an all-cast guitar.

We’ve seen some other great casting projects over the years before, too. Video after the break.

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Stop Silicone Cure Inhibition, No Fancy Or Expensive Products Required

Casting parts in silicone is great, and 3D printing in resin is fantastic for making clean shapes, so it’s natural for an enterprising hacker to want to put the two together: 3D print the mold, pour in the silicone, receive parts! But silicone’s curing process can be inhibited by impurities. What’s cure inhibition? It’s a gross mess as shown in the image above, that’s what it is. Sadly, SLA-printed resin molds are notorious for causing exactly that. What’s a hacker to do?

Firstly: there are tin-cure and platinum-cure silicones, and for the most part tin-cure silicone works just fine in resin-printed molds. Platinum-cure silicones have better properties, but are much more susceptible to cure inhibition. Most workarounds rely on adding some kind of barrier coating to molds, but [Jan Mrázek] has a cheap and scalable method of avoiding this issue that we haven’t seen before. Continue reading “Stop Silicone Cure Inhibition, No Fancy Or Expensive Products Required”

Casting Parts In Urethane: Tips From A Master

When you want a couple copies of a thing, you can 3D print ’em. When you want a ton of them, you might consider making a mold. If those are the shoes you’re in, you should check out this video from [Robert Tolone] (embedded below). Or heck, just check out all of his videos.

Even just in this single video from a couple years back, there are a ton of tips that’ll help you when you’re trying to pour resin of just the right color into a silicone mold. Mostly, these boil down to testing everything out in small quantities before pouring it in bulk, because a lot changes along the way. And that’s where [Robert]’s experience shines through — he knows all of the trouble spots that you need to test for.

For instance? Color matching. Resin dyes are incredibly concentrated, so getting the right amount is tricky. Mixing the color at a high concentration first and then sub-diluting it slowly allows for more control. But even then, the dried product is significantly lighter than the mixture, so some experimentation is necessary. [Robert] sneaks up on just the right color of seafoam green and then pours some test batches. And then he pours it in the exact shape of the mold just to be sure.

That’s just one of the tips in this video, which is just the tip of the mold-casting iceberg. Pour yourself a coffee, settle down, and you’ll learn something for sure. If you’re into more technical parts and CNC machining, we still love the Guerilla Guide after all these years.

Much thank to [Zane] for tipping us off to this treasure trove.

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A Rotocasting Machine Sized For The Home Shop

If you’ve ever wondered how large, hollow plastic structures like tanks and drums are formed, you’re in luck: [Andy] not only fills us in on the details of rotational casting and molding, but he also built this sweet little rotational casting machine to help him with his DIY projects.

Granted, [Andy]’s build won’t be making anything too large, like a car fuel tank or a kayak. Not only is it sized more for smallish parts, but those structures are generally made with the related process of rotational molding. Both processes use an enclosed multipart mold that’s partially filled with plastic resin, and then rotate the mold around two axes to distribute a thin layer of resin around the inside of the mold. The difference is that roto-molding uses a thermoplastic resin, whereas roto-casting uses resins like polyurethane and silicone that set at room temperature.

The machine looks simple, but only because he took great pains to optimize it. The videos below cover the build in detail — feel free to skip to the 11:38 mark of the second video if you just want to see it in action. Though you’ll be missing some juicy tidbits, like welding a perfect 90° joint in square tubing. There’s also the custom tool [Andy] built to splice the beaded chain he used to drive the spinning of the mold, which was pure genius.

Using the machine and a complex nine-piece mold, [Andy] was able to create remarkably detailed tires for RC cars from polyurethane resin. We’d love to see what else this rig is good for — almost as much as we want to see details on how the mold was made. We’ve seen other rotational casting machines before, but this one takes the cake for fit and finish.

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