Hackers vs. Mold: Building a Humidistat Fan

Having a mold problem in your home is terrible, especially if you have an allergy to it. It can be toxic, aggravate asthma, and damage your possessions. But let’s be honest, before you even get to those listed issues, having mold where you live feels disgusting.

You can clean it with the regular use of unpleasant chemicals like bleach, although only with limited effectiveness. So I was not particularly happy to discover mold growing on the kitchen wall, and decided to do science at it. Happily, I managed to fix my mold problems with a little bit of hacker ingenuity.

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DIY Injection Mold Design for the Home Shop

3D printing is great for prototyping, and not bad for limited runs of parts. Unfortunately though it really doesn’t scale well beyond a few pieces, so when you’re ready for the mass market you will need to think about injection molding your parts. But something like that has to be farmed out, right? Maybe not, if you know a thing or two about designing your own injection molds.

The video below comes from [Dave Hakkens] by way of his Precious Plastic project, whose mission it is to put the means of plastic recycling into the hands of individuals, rather than relying on municipal programs.  We’ve covered their work before, and it looks like they’ve come quite a way to realizing that dream. This tutorial by [Dave]’s colleague [Jerry] covers the basic elements of injection mold design, starting with 3D modeling in Solidworks. [Jerry] points out the limitations of a DIY injection molding effort, including how the thickness of parts relates to injection pressure. Also important are features like gentle curves to reduce machining effort, leaving proper draft angles on sprues, and designing the part to ease release from the mold. [Jerry] and [Dave] farmed out the machining of this mold, but there’s no reason a fairly complex mold couldn’t be produced by the home gamer.

When you’re done learning about mold design, you’ll be itching to build your own injection mold machine. Precious Plastic’s tutorial looks dead simple, but this machine looks a little more capable. And why CNC your molds when you can just 3D print them?

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Making a Gun Without a 3D Printer

Around four years ago the world was up in arms over the first gun to be 3D printed. The hype was largely due to the fact that most people don’t understand how easy it is to build a gun without a 3D printer. To that end, you don’t even need access to metal stock, as [FarmCraft101] shows us with this gun made out of melted aluminum cans.

The build starts off by melting over 200 cans down into metal ingots, and then constructing a mold for the gun’s lower. This is the part that is legally regulated (at least in the US), and all other parts of a gun can be purchased without any special considerations. Once the aluminum is poured into the mold, the rough receiver heads over to the machine shop for finishing.

This build is fascinating, both from a machinist’s and blacksmith’s point-of-view and also as a reality check for how easy it is to build a firearm from scratch provided the correct tools are available. Of course, we don’t need to worry about the world being taken over by hoards of angry machinists wielding unlicensed firearms. There’s a lot of time and effort that goes into these builds and even then they won’t all be of the highest quality. Even the first 3D printed guns only fired a handful of times before becoming unusable, so it seems like any homemade firearm, regardless of manufacturing method, has substantial drawbacks.

Thanks to [Rey] for the tip!

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A Great Way to Make Quick and Easy Knobs

Here’s a great way to quickly and easily make attractive and functional knobs with no tools required. All you need is some casting resin (epoxy would do in a pinch), a silicone mold intended for candy, and some socket head bolts. With the right preparation and a bit of careful placement and attention, smooth and functional knob ends are only minutes away. Embedded below is a short video demonstrating the process.

These may not replace purpose-made knobs for final products, but for prototypes or to use around the shop on jigs, clamps, or furniture they certainly fit the bill. With a layer of adhesive fabric or rubber, they might even make serviceable adjustable feet for low-stress loads.

This technique could be extended to reproducing broken or missing dakaware or bakelite knobs. This, of course, would require an original, unbroken knob and a small silicone mold, but it’s still a project that’s well within the capabilities of the garage-bound hacker.

While we’re on the subject of knobs, don’t forget we’ve seen an excellent method of repairing knobs as well.

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Silicone Molds for Stove-Top Metal Casting

Casting metal parts from 3D-printed plastic or Styrofoam models is all the rage these days, and for good reason — casting is a way to turn one-offs into mass-produced parts. Seems like most of the metal casting projects we feature are aluminum in sand molds, though, so it’s refreshing to see a casting project using silicone molds to cast low-melting point metals.

Don’t get us wrong — sand-cast aluminum is a great method that can even be used to build a lathe from scratch. But not everyone wants to build a foundry and learn the sometimes fussy craft of creating sand molds. [Chris Deprisco] wanted to explore low-melting point bismuth alloys and set about making silicone rubber molds of a 3D-printed Maltese falcon. The bismuth-tin alloy, sold as a substitute for casting lead fishing weights, melts on at 281°F (138°C) and is cool enough for the mold to handle. Initial problems with bubbles in the cast led to a pressure vessel fix, and a dull, grainy surface was fixed by warming the mold before the pour. And unlike sand molds, silicone molds are reusable.

Of course if aluminum is still your material of choice, there’s no need for a complicated foundry. A tuna can, a loaf of bread, and a handful of play sand is all you need to make custom parts.

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Custom Aluminum Wheels Teach a Thing or Two about Casting

For some mobile projects like small carts or rolling cabinets, your standard casters from Harbor Freight will do just fine. But some projects need big, beefy wheels, and these custom cast aluminum wheels certainly make a statement. Mostly, “Watch your toes!”

To be honest, [Brian Oltrogge]’s wheels are an accessory in search of a project, and won’t be crushing feet anytime soon. He made them just to make them, but we have no beef with that. They’ve got a great look that hearkens back to a time when heavy metal meant something else entirely, and things were made to last. Of course, being cast from aluminum sort of works against that, but there are practical limits to what can be done in the home foundry. [Brian] started with a session of CAD witchcraft followed by machining the cores for his molds. Rather than doing this as lost foam or PLA, he milled the cores from poplar wood. His sand mix is a cut above what we usually see in home-brew sand casting — sodium silicate sand that can be cured with carbon dioxide. All his careful preparation meant the pour went off without a hitch, and the wheels look great.

We’ve featured quite a few metal casting projects recently, some that went well and some that didn’t. [Brian] looks like he knows what he’s doing, and we appreciate the workmanship that he puts on display here.

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Fail of the Week: Sand Casting Copper

There’s trouble in the Kingdom of Random – the smithies of the realm are having trouble sand-casting copper. And while [King Grant] might not be directly asking for help, we think the Hackaday community might have plenty to say about his efforts.

We’ve all seen plenty of sand casting efforts before, including attempts to make otherwise unobtainable engine parts. And “lost foam” casting, where a model of the part is constructed of polystyrene foam that flashes off when the molten metal is poured, is a relatively new twist on the technique that’s been used to good effect on a recent Gingery lathe build. But most backyard foundries work in aluminum, which is apparently much easier to work with than the copper that [Grant Thompson] is working with. Ironically, his first pour worked the best — not perfect, but at least the islands defining the spokes of his decorative piece didn’t break off and float away as they did in every pour shown in the video below. That leads us to think that the greensand is too dry by the second video. Or perhaps the density of copper just makes it more likely for the sand to float. Maybe a cope and drag mold is in order to keep the islands in place and direct the flow of the copper better.

We know there’s a lot of expertise out there, so sound off in the comments about what you think is going on with these pours.

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