Cans to Metal

I was always told that the first thing you need to know about melting aluminium cans is that you don't really want to melt aluminium cans; it's too hard. Find other chunkier scrap aluminium instead. But I'm a sucker so I did it anyway.


The big problem is that there is a lot of surface area on the cans, and that this encourages the aluminium to oxidise. Oxidised aluminium holds on to the liquid aluminium like a sponge, so unlike when you melt lead or pewter the metal does not all automagically drop to the bottom. It needs fluxes, chemicals, special furnaces and the like. Yeah, right.


So, take a load of heatproof bricks or pavers and in a stable location away from flammable stuff construct a sturdy furnace. You'll note that mine is built from ordinary pavers on a mud bank, surrounded by foliage, and looks like it'll collapse at any moment. The trick is to have a long tunnel going into the bottom of the furnace, with a little doorway on top to allow you to put things in and take them out. The chimney takes the sparks up and away from your face and hair, and needs to be narrower than the furnace bottom.


Down the tunnel, you direct a hair-dryer, blower, hot-air stripper (good idea Forrest!), powerful fan or similar. This encourages flames and sparks from ordinary BBQ charcoal at the bottom of the furnace. Do not place the fan up against the tunnel or it may get flamed. If I need to tell you to keep a bucket of water and hose at hand, and warn you not to wet the fan you really shouldn't be doing this.


Back to the cans. Flatten these as much as possible and pack the flattened remains hard into a steel can. This steel can lasts only one burn, so pack in as much as you can.


Now light the furnace. A couple of lit newspaper balls in the tunnel generally does the trick, or poke a blowtorch in there. Once you turn the fan on it's a matter of moments before the whole thing flares up. Once it's going turn off the fan, open the door and rearrange the charcoal so you can put the can inside. Put more charcoal against the can, close the door and turn the fan on again. At this point you realise the value of some peep-hole or crack through which you can watch the inferno.


When the can is orange hot the contents miraculously shrink. once everything in the can is a nice, bright orange, turn off the fan and take it out - I use BBQ tongs. Rattle the contents about a bit, then turn it upside-down on a wide fireproof surface. Squish the pile of dross and molten aluminium streams out. Try to round these up into big blobs so they don't oxidise much when you re-melt them.

Now you have reasonably-sized lumps of aluminium that you can do traditional backyard casting with.

Drilling Down The Middle

We've all tried to do it - drill a hole down the middle of a bolt or rod. Making steam engines, nozzles, RepRap parts, air gun barrels, whatever it is physics conspires against us, and the hole never goes straight. But it can be done in a hobbyist drill press - the type that holds a power drill - by making physics work for us.

First off, the drill press itself must be reasonably solid. So, no pressed metal, no tubing, no plastic clamps. Get a good, solid cast-iron cheap one with a solid post. They churn them out in China and I paid NZ$30 for mine. You will need a drill vise that fits the drill press. Pick one with a small notch in the middle of the jaws.

Next, the power drill. You'll need one with variable speed. Make sure hammer drill options are turned OFF or you will smash things to bits. Being in "forward" helps too. Finally, make sure your drill bit is sharp. Sharpening by hand is really quite easy and a badly hand-sharpened bit is more use than an old, dull bit anyway.

Put the drill bit hand-tight in the chuck the wrong way round. Lower the press so that the bit can be clamped in the vise. Tighten the vise and bolt it firmly to the drill press base. Tighten the clamp that holds the press mechanism to the post. Now loosen the chuck and slowly raise the drill. Do not let it fly up or it'll whack itself out of alignment.


Place the bit of rod or bolt that you want to drill into in the drill chuck. Tighten it up and make sure it and the bit are still central. Using high speed and very little pressure, lower the drill onto the bit. This will cause a little vibration initially, but soon small turnings will fall and the drill bit will automatically "hunt the centre." Slow the drill right down and gradually increase the pressure.


You want to see gleaming, long streams of swarf coming out, not many little fragments. If swarf stops coming out or you see smoke, stop and clear the bit with something pointy. Fingers are a poor choice as the bit will likely be damn hot and the swarf is really sharp to boot.

For deep through holes, stop half way (mark the bit with a pen), reverse the part in the chuck, and start again. There will be a little jamming as the two holes meet - go through it and the result is a beautifully central hole!

I mostly do this with brass, but if you do it with steel you'll need coolant/lubricant. It comes in cans at the DIY store. So there you go. Neat, central holes.

Vik :v)

Webcam Monocle

Suz got me a wonderful Logitech webcam for Christmas. It plays nicely with Linux but it did not have adjustable focus and so was difficult to use in a benchtop setting. I attached the webcam to my swivel lamp so that it can be positioned anywhere on the bench and illuminated simultaneously if desired.



The focus was a problem for closeups, so I cut a pair of dollar-store +3 reading glasses in half and wrapped the earpiece around the back of the webcam. With a little encouragement it clips the lens over the flat part of the webcam's orb where the lens peeks out. Perfect.




As you can see from the photo, the focus fades out before my workshop does, but I can get in much closer to the masterpieces in progress on the bench.

Vik :v)

Eliminating Trapped Gas

I shoot CO2-powered airguns a fair bit for amusement and vermin control, but some guns get through more gas than others. Unfortunately, if you leave a CO2 cartridge in the gun for more than a week or so you risk getting it stuck against the seal - my possum carbine may sit there for a month without seeing action in the winter. Lubricants like molylube and silicone grease just muck things up, so I tried PTFE threadseal tape:


It works really well. As an added precaution, change the cartridge when there is a small amount of gas remaining to blow the spent cartridge cleanly off the seal.

The tape goes just once neatly over the cap on the end of the cartridge, back down to the shoulder, then wraps around a couple of times to stop the tape coming off in the guts of your airgun. Don't put on too much tape if loading into a tight-fitting or corroded cartridge holder or you might wedge it in.

Vik :v)

Father's Day 2009

Well, locally it's Father's Day. I had a very nice breakfast cooked for me by my daughters, and was then presented with the following very appropriate card:


Note the garnish of bright orange G-clamps, and a dash of camouflage gaffer tape on the otherwise black tape card. MacGyver would have been proud. I certainly was.

Vik :v)

The Spoondriver

Being in search of a way to build repraps, I pondered on ways to remove the need to solder circuits together, and an electric motor or heater driver seemed like low-hanging fruit. Go minimalist, I thought. "What would McGuyver do?" I asked myself. Then a hunger pang led to the thought of the awful cheap spoons in the kitchen, and an evil plan formed.

Well, evil if you're a spoon.


The simple solution does away with circuit boards and solder altogether. Three cheap components here to get from the electronics store: A TIP120 series transistor (121 or 122 is fine), a honking big diode (IN4007 or IN5404 are good) and a 1K resistor (any size, brown-black-red lines on one end). Get some small terminal strip while you're there. All the bits look completely different and have an obvious way round when it matters. If you're smart enough to figure out that the insulation needs to be stripped off the wiring before it goes into the terminal strip, you can build this driver.

Shove the leads in the terminal strip - not too far or you'll stop the wires coming in the other end. This might involve technical things like cutting the component wires shorter. In the pictures, the big red & black wires are +12 volts and ground. The yellow wire is the signal wire that connects to your Arduino, clone or Pinguino. The thin black and red wires connect to the load, in this case a small fan. It matters which way round those fan wires go.

It works. But it needs a heatsink to drive loads of a few amps. Bad news for spoons. Having torn off its head, I filed over the wound, bashed its neck flat, drilled a 3mm (1/8") hole in it and bolted it to the hot transistor. Bwahahaha.

The other stuff is an EasyDriverV3 stepper driver that needs eight wires soldered to it to make a stepper motor move. The cheap little switches will replace the opto sensors. That'll have to do for this round of reprap simplification.

So, spoons, don't mess with me!

Vik :v)

Kettle with temperature readout

My wife needed a source of water for a speciality diet food - let's just call it "Optipuke" - that was at a temperature of 50 degrees C. Any more, the medical qualities of said food got lost. Any less and it tasted somewhat tepid and even worse than usual. Kettles seldom come with a temperature readout, so I purchased a US$8 probe thermometer rated at 150C from DealExtreme (I have an addiction). Fortunately our kettle fills through the spout, so the lid was free to play with. The only other thing I needed was a 10mm long piece of silicone tubing (rated to 300C) that just fitted over the probe.


I took the knob out of the lid, which left a hole that was conveniently just the right size for the thermometer. I then inserted the probe and slid the piece of silicone tubing firmly up to the top . This is essential to stop steam coming out of the lid hole, and stops the display rotating when you move the kettle. The probe I bought seems to be reasonably resistant to steam, and so my wife's dietary needs are now met.

As a bonus, when the diet is done I can dismantle it all and still have a functioning kitchen thermometer.