Saturday, September 18, 2010

My First Brass Rorschach Test

That's a lump of yellow brass, with a bit of copper wire dissolved in it. Things had to be beyond yellow hot to make it melt, and I had difficulty maintaining the heat around the little steel crucible - the charcoal needed nearly continuous tamping. I've figured out that dry bits of 20x20x80mm dry wood seem to be about right to maintain a stream of nice charcoal at the bottom of the furnace. The sweet spot isn't very big, so a crucible half the height of my current one is realistic.

I'll have to work on channelling the air to a more precise point, and getting the fuel funnelling into a smaller hot zone. I'm going to need a lot of fuel when I try melting iron, just for weight to ensure the air blast doesn't blow it all out the chimney!

Experiments have revealed the amazing coincidence that a beer can is about the right size for the furnace core of a mini-cupola that I might be able to power with a cheap leaf-blower. Well, I've managed to melt the end of the hot air stripper anyway...

Thursday, September 2, 2010

Electronic Sliding Door Lock

I couldn't find an electronic door latch for my workshop door, so I made one. I just used a secure car central locking kit with 2 remotes and a slave solenoid. I Made the contacts from biro springs and empty .22 cartridge cases. Shouldn't have trouble making it work off 12V battery backup either, but for the moment SWMBO just wants it mains-powered.

Sunday, August 8, 2010

We Melted Gold(ish)!

Kate had a bunch of copper wire clippings spare, so I tried melting them in the furnace. Using a sawn-off steel CO2 container with its bottom flattened as a crucible and the sawn-off bit poked into the top to reduce oxidation. I also added a bit of glass to float any slag.

As you can see, I managed to get it up to a fair old temperature, glowing yellow hot and some. The copper melted inside the container with an amazing amount of outgassing.

So the picture makes it look like gold, but it was copper. Not that there's much of a difference in melting point. The big surprise is that it came out as bead-like globules. Hopefully a clean re-melt will fix it.

This melt was done with homemade charcoal, which produced an excellent heat. Next I'll be using smaller chunks, and mould a sloping trench to direct the charcoal into the path of the incoming air blast. Out into the rain we go to mould the clay while it's damp...

Saturday, July 31, 2010

Can Melting Update

Using the bottom of a MAPP gas can, which is larger and sturdier than a coconut cream tin, I've managed to melt and cast 20 cans at a go - and I still have a lot of my $6 bag of BBQ charcoal left.

When you get enough in the can, the aluminium squeezes out of the dross easier and you can pour it directly into a mould.

Friday, July 23, 2010

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.

Thursday, February 25, 2010

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)

Thursday, February 4, 2010

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)