Chain Mail Experiment

Medieval armor is an interesting subject, and while I don’t have much interest in acquiring any or joining in for any re-enactments, I was curious about how it is made, and what it behaves like.

With a bit of scrap galvanized wire I had laying around, I took a bit of time one evening to wrap it into a spring on my lathe, cut it into rings, and then form the rings into a small chunk of chain mail.

I’m pretty pleased with the results. It’s a neat bit of material that came out, albeit very time consuming to produce.

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Propane Burner

While charcoal and a blower works OK for the aluminum melting projects I’ve been doing, I was getting frustrated with the mess, hassle, and cost of that setup. The charcoal created ashes that sometimes got into the aluminum and needed to be cleaned up in general, there were a lot more parts involved to get a working setup, and it had to be constantly fed new charcoal, and while charcoal isn’t terribly expensive, a propane torch would get a few melts out of a barbecue sized propane tank, and make the process cheaper.

So, using this video as a reference, I made my own torch and gave it a test. Additionally my sister and brother-in-law gave me a new graphite crucible, which has also greatly improved the melting process.

I had a whole bunch of cans saved up, mostly from folks who have saved cans for me and brought them over. I had somewhere around four garbage bags full of cans to melt down. The propane burner and graphite crucible handled them with ease!

In all, I melted down around 315 cans, and ended up with just over 6 pounds (~2.7kg) of aluminum cast into heart shaped ingots.

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Fire Piston

I’ve really been enjoying watching Clickspring’s videos recently, and it encouraged me to make one of his projects as a christmas gift for my father. As someone who’s into the outdoors, I thought a fire piston would be the perfect choice.

I had some aluminum round stock laying around in my (albeit small) scrap pile, and spent a few hours on the lathe shaping it into a functioning fire piston.

The fire piston is a really simple device, which uses a rod shoved into a cylinder sealed with O-rings, to suddenly compress the air inside, which will heat it up enough to ignite some material. Char cloth is commonly used.

The char cloth provides a burning ember that you can apply to your tinder and start a fire.

No matches, just the laws of physics!

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Testing Self Clinching Standoffs

I’ve recently been looking at better ways to mount a PCB inside a metal enclosure. Primarily I’m interested in ways that don’t require screws protruding from the bottom.

I found these self clinching standoffs on Fastenal’s web site, and figured I’d give them a try. Normally they’re installed using an automated press, but I gave it a shot with the cheap Harbor Freight press I’ve got.

Apologies for the vertical format video. Handling the camera, the metal, and the press at the same time was a bit unwieldy.

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Binary Addition Machine

A few years ago, the idea came to me to build a binary addition machine as a display piece. The logic would be constructed of SPDT (Single Pole Double Throw) relays, which reduces the number of relays and simplifies the design a bit. The schematic represents a single Full Adder, eight of which will compose the full addition machine.

Note that A and B are the inputs from the two numbers, S is the output, CarryIN in the input from the previous bit, and CarryOUT is the output to the next bit.

My original efforts on this project were based on home etched PCBs, using the photo etching process I’ve posted about in the past on this blog. Here’s an example of one of the single sided boards I designed to compose a single Full Adder.

You’ll notice that some areas of the ground plane on the PCB seem to get a little spotty. It’s important to make sure you get the settings on your printer as dark as possible to avoid this. After tuning for my printer, I came up with the darkest print I could manage. The old transparency is on the top, and the new is on the bottom.

As you can see, it is a good bit darker on the new print, which leads to better etchings.

However, the whole process of exposing, etching, and cleanup is rather fiddly and time consuming, so I never managed to get around to making all eight Full Adders required to complete the machine.

Several years went by with the project languishing in my random electronics box, and was recently brought back to light. I decided that I was going to design a new board and have it professionally made to save the time, and have a better looking end result, and work on making the mount and the various other bits as pretty as possible since the goal was a display piece.

I ordered the PCBs and the parts to populate them, and in the meantime started work on laying out the mounting on a piece of Oak I picked up from the hardware store.

Once the mounting was all sorted out, there was lots of sanding and lacquering.

I decided I wanted to etch the labels into the brass plate that would hold the 16 bit switches (two eight bit numbers that get added together).

The etching turned out really well!

The display plate also got put together with nine LEDs (the 8 bit number and a 9th for the carry).

Instead of buying brass standoffs that would go with the switch and display plates, I bought a section of brass tubing, cut it down into equal lengths, trimmed the ends on my lathe, and brushed them with a wire wheel on my grinder.

Finally, it was time to assemble the boards.

And then get them mounted on the base.

In the end, I’m extremely pleased with how this project came out, it’s a beautiful result, and is really fun to show people how the math works here. It’s also really neat to see the propagation delay in a multi-bit carry due to the relay switching times.

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