Furnace – MARK 3 (by alaric)

Ok! Right!

Furnace Mark 1 was made in a coffee can, and was a bit too small. The crucible it was designed for was too small to pour some of the things we decided we wanted.

So we made the Mark 2, which was bigger. And then it was nearly ruined when a crucible (thin steel cup, since I can't find any iron pipes anywhere, and couldn't weld until recently) leaked molten Al everywhere, so we moved up to Salamander crucibles. And then we had to make crucible tongs, since we couldn't fit them with lifting lugs. And the Mark 2 turned out to not have enough clearance to fit the tongs around a crucible inside, as well as the inside having gotten rather crumbly and fallen to bits a lot. We tried to chop it down the side so one half of it (except for the base) could be removed to get the tongs in, but it just turned to power.

So on to Mark 3. Read more »

New welded tongs (by alaric)

Today my mate Mike and I made new crucible tongs.

Check out my dodgy welds:

Read more »

Arc welding (by alaric)

As a treat, I've bought myself a manual metal arc welder!

Manual metal arc welding, however, is quite tricky to learn. Basically, the stages are:

1. Being able to make the thing go at all. You need to create an arc, then maintain it, which needs a fair amount of practice and dexterity.
2. Being able to then move the arc at the desired rate, in the desired direction, to leave a weld behind.
3. Being able to do this well enough to produce a strong weld, rather than a rough blobby one that's only attached here and there
4. Being able to do this well enough to produce a neat weld, which is the same as the previous hurdle, but now keeping the weld the same thickness all along, and nice and smooth
5. All of the above again, but under trying circumstances such as when the objects being welded aren't nice and conveniently placed in front of you

I've just managed 1 today, and am part way through 2!

My medium-term goal is to make new crucible tongs - the previous ones are OK, but a little hair-raising to use since they don't grip the crucible perfectly. They were made by bending single lengths of steel, which constrained them a little. With welding mastered, I should be able to make crucible tongs that fit around the crucible much more snugly, so requiring less wiggling to get them in the clearance between crucible and furnace wall, and then a tighter grip of the crucible itself rather than just squeezing it at a few points...

Arc welding is fun!

New crucibles (by alaric)

Just before the wedding, I got two crucibles. Proper A4 salamander crucibles, made from some refactory stuff, rather than stainless steel cups as I'd been using up to then.

However, the stainless steel cups are easy to lift - I punched holes in the sides near the top and put bolts through, so the thing could be lifted using barbeque tongs (the wire loops of the tongs slip over the bolts, securing the crucible). The salamander crucibles, being made of a clay-like stuff, cannot simply be drilled and fitted with lugs; the material wouldn't take the strain when at red heat.

So I had to make tongs. I picked up two 7mm square cross section iron rods from B&Q, a metre long each, and forged them into tongs by using the torch to take parts of them up to red heat, then banging them with a hammer on top of an old steel beer keg or bending by (heatproof gloved!) hand, until they had curved bits that cupped the bottom of the crucible, and met at the top with a hinge.

Well, getting the two bits the right shape for the crucible AND meeting up at the top was pretty tricky, and then we had trouble drilling through the things (using a high speed Dremel was a mistake that got the drill bits hot enough to destroy their hardening; had to use the Black & Decker to drill the holes slowly... although I only have a drill press for the Dremel. Luckily, the hole I'd made drestroying drill bits in the dremel acted as a started hole for the big hand drill). So the tongs are a bit... imperfect.

If I could weld, I could make proper ones or do what the other guys do, which is to make highly durable, large, stainless steel crucibles (as opposed to my little cups) out of thick-walled steel tubing. Not that I've ever found any thick-walled steel tubing lying around as they all seem to.

As it happens, it turns out I need a second person to use a hooked rod to make sure the crucible doesn't fall out of the tongs when I'm pouring... Ok, I don't want to do melts without another person in case I have an accident anyway, but it's wasteful to need two people to do the job of one.

Anyway, at least the things worked, enabling me to use my nice proper crucibles. It takes a long time to heat up the 1cm-thick walled clay crucible compared to my 2mm-thick steel cup, but once it's all glowing red hot, it sure melts stuff fast. What's more, it keeps the aluminium hot once I've lifted it from the furnace and while I'm pouring, enabling me to take it a bit easier in this delicate stage!