Sharpies and Glue Sticks Fight the Gummy Metal Machining Blues

“Gummy” might not be an adjective that springs to mind when describing metals, but anyone who has had the flutes of a drill bit or end mill jammed with aluminum will tell you that certain metals do indeed behave in unhelpful ways. But a new research paper seeks to shed light on the gummy metal phenomenon, and may just have machinists stocking up on office supplies.

It’s a bit counterintuitive that harder metals like steel are often easier to cut than softer metals; especially aluminum but also copper, nickel alloys, and some stainless steel alloys. But it happens, and [Srinivasan Chandrasekar] and his colleagues at Purdue University wanted to find out why, and what can be done about it. So the first job was to get up close and personal with the interface between a cutting tool and metal stock, to observe the dynamics of cutting. In a fascinating bit of video, they saw that softer metals tend to fold in sinuous patterns rather than breaking on defined shear planes.

Source: American Physical Society.

Having previously noted that cutting through Dykem, a common machinist’s marking fluid, changes chip formation in soft metals, the researchers tested everything from Sharpies to adhesive tape and even correction fluid, and found that they all helped to reduce the gumming action to some degree. Under their microscope they can clearly see that chips form differently once the cutting edge hits the treated surface, tending to act more brittle and ejecting rather than folding. They also noted a marked decrease in cutting force for the treated metal, and much-improved surface finish to boot.

Will Sharpies and glue sticks enter the book of old machinist’s tricks like gauge-block wringing? Only time will tell. But for now, this is a pretty fascinating bit of research that you might be able to put to the test in your shop. Let us know what you find in the comments.

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Harley-Hardened Wire Helps High-Gain Antenna Hack

What does a Harley-Davidson motorcycle have to do with building antennas? Absolutely nothing, unless you happen to have one and need to work-harden copper wire to build a collinear antenna for LoRa.

We’ll explain. Never being one to settle, [Andreas Spiess] needed a better antenna for his LoRa experiments. Looking for high gain and an omnidirectional pattern, he bought a commercial colinear antenna, which is a wire with precisely spaced loops that acts like a stack of dipoles. Sadly, in a head-to-head test [Andreas] found that the commercial antenna was no better than lower gain antennas in terms of range, and so he decided to roll his own.

Copper wire is a great material for antennas since it can be easily formed without special tools and it solders like a champ. But the stuff you get at the home center is nowhere near stiff enough for a free-standing vertical whip. This is where the Harley came in: [Andreas] used his Hog to stretch out the 1.75-mm diameter (a little bigger than #14 AWG) copper wire. Not only did the work-hardening stiffen the wire, it reduced its diameter to the 1.4 mm needed for the antenna design. His vector network analyzer told him that ground-plane elements and a little fiddling with the loop diameter were needed to get the antenna to resonate at 868 MHz, but in the end it looks like the antenna is on track to deliver 5-dBi of gain.

Of course there are plenty of other ways to stretch out a wire — you could just stretch it out with hanging weights, or even with a go-kart motor-powered winch if you’re ambitious. But if you’ve got a bike like that, why not flaunt it?

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The Best Part of Waking Up Just Got Better

If you ask us, one of life’s greatest pleasures is sitting down with a nice, hot cup of something of coffee, tea or hot chocolate. Of course, the best part of this ritual is when the beverage has cooled enough to reach that short window of optimal drinking temperature.

Often times the unthinkable happens—we sip too early and get burned, or else become distracted by watching cat videos reading our colleagues’ Hackaday posts and miss the window altogether. What’s to be done? Something we wish we’d thought of: using the beverage’s heat to cool itself by way of thermal dynamics. For [Scott Clandinin]’s entry into the 2018 Hackaday Prize, he hopes to harness enough heat energy from the beverage to power a fan that will blow across the top of the mug.

[Scott] enlisted a friend to smith a thick copper slab in a right angle formation. The gentle curve of the vertical side pulls heat from the ceramic mug and transfers it to the heat sink of a CPU cooler. Then it’s just a matter of stepping up the voltage produced by the thermoelectric generator with a boost converter. Once he’s got this dialed in, he’d like to power it with supercaps and add a temp sensor and a microcontroller to alert him that his moment of zen is imminent. We’ll drink to that!

The Aluminum Wiring Fiasco

Someone who decides to build a house faces a daunting task. It’s hard enough to act as the general contractor for someone else, but when you decide to build your own house, as my parents did in the early 1970s, it’s even tougher. There are a million decisions to make in an information-poor and rapidly changing environment, and one wrong step can literally cast in stone something you’ll have to live with forever. Add in the shoestring budget that my folks had to work with, and it’s a wonder they were able to succeed as well as they did.

It was a close call in a few spots, though. I can recall my dad agonizing over the wiring for the house. It would have been far cheaper to go with aluminum wiring, with the price of copper wire having recently skyrocketed. He bit the bullet and had the electrician install copper instead, which ended up being a wise choice, as houses that had succumbed to the siren call of cheaper wiring would start burning down all over the United States soon thereafter.

What happened in the late 60s and early 70s in the residential and commercial electrical trades was an expensive and in some cases tragic lesson in failure engineering. Let’s take a look at how it all happened.

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Fail of the Week: The Spot Welder Upgrade That Wasn’t

Even when you build something really, really nice, there’s always room for improvement, right? As it turns out for this attempted upgrade to a DIY spot welder, not so much.

You’ll no doubt recall [Mark Presling]’s remarkably polished and professional spot welder build that we featured some time ago. It’s a beauty, with a lot of thought and effort put into not only the fit and finish but the function as well. Still, [Mark] was not satisfied; he felt that the welder was a little underpowered, and the rewound microwave oven transformer was too noisy. Taking inspiration from an old industrial spot welder, he decided to rebuild the transformer by swapping the double loop of battery cable typically used as a secondary with a single loop of thick copper stock. Lacking the proper sized bar, though, he laminated multiple thin copper sheets together before forming the loop. On paper, the new secondary’s higher cross-sectional area should carry more current, but in practice, he saw no difference in the weld current or his results. It wasn’t all bad news, though — the welder is nearly silent now, and the replaced secondary windings were probably a safety issue anyway, since the cable insulation had started to melt.

Given [Mark]’s obvious attention to detail, we have no doubt he’ll be tackling this again, and that he’ll eventually solve the problem. What suggestions would you make? Where did the upgrade go wrong? Was it the use of a laminated secondary rather than solid bar stock? Or perhaps this is the best this MOT can do? Sound off in the comments section.

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Tinning Solution From the Hardware Store

Making your own printed circuit board at home often leads to a board which looks homemade. Exposed copper is one of the tell-tale signs. That may be your aesthetic and we won’t cramp your style, but exposed copper is harder to solder than tinned copper and it likes to oxidize over time. Tinning at home can bring you a step closer to having a full-featured board. In the video after the break, famed chemist [nurdrage] shows us how to make tinning solution at home in the video below the break.

There are only three ingredients to make the solution and you can probably find them all at a corner hardware store.

  • Hydrochloric acid. Also known as muriatic acid.
  • Solid lead-free solder with ≥ 95% tin
  • Silver polish containing thiourea

Everything to pull this off is in the first three minutes of the video. [nurdrage] goes on to explain the chemistry behind this reaction. It doesn’t require electricity or heat but heat will speed up the reactions. With this kind of simplicity, there’s no reason to make untinned circuit boards in your kitchen anymore. If aesthetics are very important, home tinning yourself allows you to mask off certain regions and have exposed copper and tin on the same board.

[nurdrage] is no stranger to Hackaday, he even has an article here about making your own PCB etchants and a hotplate to kick your PCB production into high gear.

Thanks for the tip, [drnbutyllithium].

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Harvesting Copper from Microwave Ovens

Obsolete appliances were once a gold mine of parts, free for the taking with a few snips of your diagonal cutters. Times have changed, though, and most devices yield only a paltry supply of parts, so much so that only by harvesting raw materials can you get much value out of them. And so we have this example of reclaiming copper from used microwave ovens.

The primary source of copper in most microwaves is the transformer, which we usually see re-tasked for everything from spot welders to material handling electromagnets. But the transformer is not the only source of the red metal; [eWaste Ben] also harvests it from relay coils and the main coil and shading coils of the fan motor.  The bounty is melted down in an electric foundry and cast in a graphite mold into a lovely ingot.

Unless you’re into repeatedly casting copper trinkets, a large bar of reclaimed copper might not be something you have a burning need to possess. But bearing in mind that copper can go for about $2.50 a pound at the scrap yard, there’s some money to be made, especially with dead microwaves essentially free for the taking. As [Ben] points out, taking the extra step to melt and cast the copper harvested from microwaves makes no sense if all you’re going to do is sell the scrap, but it’s nice to know how to do it just the same.

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