Metal Casting With Single Shelled PLA Masters

[3DTOPO] does a lot of metal casting (video link, embedded below). That’s obvious by the full and appropriate set of safety gear, a rarity on YouTube.

They had all the equipment to do it the normal way: craft or CNC out a master, produce a drag and a copy, make any necessary cores, and finally; pour the mold. This is a long and tedious process. It has a high rate of error, and there is a parting line.

Another set of methods are the lost ones. With these methods the master is produced out of a material like foam or wax. The master is surrounded by refractory and then melted, burned, or baked out of the mold. Finally the metal is poured in. Theoretically, a perfect reproduction is made without ever having to open the mold.
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Wrangling High Voltage

Working with high voltage is like working with high pressure plumbing. You can spring a leak in your plumbing, and of course you fix it. And now that you’ve fixed that leak, you’re able to increase the pressure still more, and sometimes another leak occurs. I’ve had these same experiences but with high voltage wiring. At a high enough voltage, around 30kV or higher, the leak manifests itself as a hissing sound and a corona that appears as a bluish glow of excited ions spraying from the leak. Try to dial up the voltage and the hiss turns into a shriek.

Why do leaks occur in high voltage? I’ve found that the best way to visualize the reason is by visualizing electric fields. Electric fields exist between positive and negative charges and can be pictured as electric field lines (illustrated below on the left.) The denser the electric field lines, the stronger the electric field.

The stronger electric fields are where ionization of the air occurs. As illustrated in the “collision” example on the right above, ionization can happen by a negatively charged electron leaving the electrically conductive surface, which can be a wire or a part of the device, and colliding with a nearby neutral atom turning it into an ion. The collision can result in the electron attaching to the atom, turning the atom into a negatively charged ion, or the collision can knock another electron from the atom, turning the atom into a positively charged ion. In the “stripping off” example illustrated above, the strong electric field can affect things more directly by stripping an electron from the neutral atom, again turning it into a positive ion. And there are other effects as well such as electron avalanches and the photoelectric effect.

In either case, we wanted to keep those electrons in the electrically conductive wires or other surfaces and their loss constitutes a leak in a very real way.

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New CNC Machine? DIY Machinable Wax!

The folks at Leeds Hackspace have built themselves a shiny new C-beam based CNC mill. As you might expect everyone wants to try the machine out, but there’s a problem. A CNC machine presents a steep learning curve, and a lot of raw materials (not to mention cutting bits) can be used in a very short time. Their solution is simple: mix themselves some machinable wax from LDPE pellets and paraffin wax, then easily recycle their swarf and failed objects back into fresh machinable wax stock.

Making the wax recipe is not for the faint-hearted, and involves melting the LDPE pellets and wax to 130 degrees Celcius in a cheap deep-fat fryer. They bought the cheapest fryer they could find at the British catalogue retailer Argos, you really wouldn’t want to risk an appliance you cared about in this exercise.

Colouring came from an orange wax crayon, though they note recycling of mixed colours will inevitably result in a muddy brown. The finished mixture was poured into Tupperware lunchboxes to set, and the resulting blocks were trimmed to square on a bandsaw. The Tupperware proved not to have a flat bottom, so later batches were cast in a loaf tin which proved much more suitable.

We’ve mentioned the machinable wax recipe before here at Hackaday, but it’s worth returning to the topic here with a description of it being used in the wild. Having watched other environments get through learning materials at an alarming rate with very little to show for their effort, we can see it makes a lot of sense as a training material.

[Dino] Brings the Waterproof Fire

firestarter

For many of our parents, grandparents, and great grandparents, the things we consider hacking, making, and doing weren’t just for fun. They were important skills that could help one survive. This week [Dino] shows us something his dad taught him: waterproof fire starters. The trick is paraffin wax. [Dino] starts by melting down some wax in a pot. He then dips strips of newspaper in the liquid wax. Several strike anywhere matches also get the wax treatment, are then placed on the newspaper. The newspaper and matches are rolled up into a tight bundle, which is itself dipped in wax several times.

The resulting small bundle of waxed newspaper and matches is safe and easy to carry in pocket or backpack. It also becomes the perfect wet fire starter. The “newspaper shell” is torn off into strips of waxed paper, which burns slowly and allows the tinder and wood to catch. [Dino] demonstrates his pioneering skills by starting a fire at the end of the video. When the inevitable zombie apocalypse hits, we definitely want [Dino] at the Hackaday compound.

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Make your own machinable wax

wax

No matter how easy it is to throw a piece of metal or plastic onto a tool and start making chips, the price of materials does add up. [rawkstar320] has been using machinable wax – a very hard wax that is up to the task of being cut with tools spinning at thousands of RPM – to reduce his material cost, simply remelting every part with a mistake. This wax can be made at home, it turns out, and [rawkstar] is glad to walk us through the process.

The creation of machinable wax begins by melting a few pounds of paraffin wax in a home deep fryer. Machining pure paraffin would gum up the works of just about any machine, so [rawkstar] throws a few plastic polyethylene bags into the already melted wax.

After casting and cooling, these blocks of wax are ready to be surfaced with a tool and milled into any part [rawkstar]’s workshop is capable of. As a bonus, all of the chips produced from this wax can be recycled and melted down again making for a somewhat renewable material that is perfect for prototyping or casting.

3D Print in Wax, Cast in Metal

What does dry ice, ethonal, wax beads, and a blender have in common? It was the first attempts at making media for this wax 3D printer that [Andreas] has been building up. Wanting to produce 3D printed objects out of metal, and finding that direct metal laser sintering machines were still out of reach of reason, he set out to find a different way.

After trying a few different methods of making the powdered wax himself, he decided that it was much more time effective to just buy the stuff. Using the commercially available powered wax mixed with activated carbon, and a custom printer, the wax is blasted with a moderately high powered laser. More wax powder is applied over the freshly sintered layer, and the 3d part is built upwards. Once he has the part in wax, he can then make a mold of it and cast metal using the Lost Wax Casting method.

While the quality is not perfect, and you still need a roughly 2500$ laser setup (which was borrowed from his school) its surely a step into the future.

Join us after the break for a quick video.

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Printable wax as PCB etch resist

What if there were only two steps for making your own printed circuit board; print, etch? That’s what [Jeff Gough] has been working on and he presented the process in his talk at 27C3. In the first portion of the video after the break [Jeff] talks about various industrial PCB manufacturing processes in a depth you may not have heard before. We found it to be interesting but at about thirty minutes into the clip he begins the presentation of his modified printer. It’s an inkjet that can print wax onto copper clad board. The wax acts as a resist for chemical etchants, and provides very high resolution. He’s using a heavily modified print head, which brings to mind that diy piezo inkjet head which also has wax printing in its future plans. This certainly seems promising and if the process can be simplified it might do away with the toner transfer method.

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