Furnace Mark II–Part 1

Well, since I have 2/3rds of a barrel left over from starting the Mulling Machine … I might as well start making my new furnace.

I cut the barrel with an angle grinder and then smoothed down the sharp edges with a coarse round file. The edge was then folded over using a shifting spanner to bend the metal 90 degrees and then a panel beaters hammer to increase the angle to about 120 degrees (that’s a guess … I didn’t have a protractor). Next I rolled the barrel over onto the pallet and belted the crap out of it with a ball peen hammer to complete the roll. The only real reason to roll over the edge is to completely remove any sharp edges. I don’t like being cut. Apart from that, the rolled edge makes the overall edge more even.

When the furnace is lined with refractory the rolled edge should be under the refractory anyway, so it isn’t like the edge is going to be all that dangerous anyway. Certainly not more dangerous than what’s going to be going on inside the furnace.

Because the mulling machine has more of a need for a complete surface, and because the base of the furnace is going to be lined with refractory, I opted to use the end with holes for the furnace. The screw caps are sitting in my workshop, and I’ll put them back in before I start to line the furnace … although … the large port may be useful to keep for allowing spills to escape from the furnace (I haven’t had a spill in my furnaces yet, but they can be a pain to clear.

So … that’s where we are at so far. This furnace will be much bigger than my current flowerpot furnace and I should be able to get more into it. I may need to get a bigger crucible.

Muller–Part 1

Here I am starting my new mulling machine. Actually, the muller will be used to mull greensand and also can be used to crush glass.

I plan to crush glass for glazing and playing with glass drawing etc.. so, big plans for this tool.

Essentially, the muller is going to be made from 1/3rd of a 44 gallon steel barrel. The barrel will get a central shaft that extends beyond the bucket. At the top, the shaft will simply attach to a pivot, while the bottom will attach to a belt, so that the muller can be driven by a motor.

So far, the muller is only the bucket.

I’ve started to roll the edge at the top so that I can weld some cross-braces. The cross braces are just steel rods (steel reo actually). They will be welded to the central shaft and to the lip of the muller.

I have a steel ball that is used for crushing concrete. I’ll also be welding some paddles inside the bucket so that the ball bounces and the mix will fold.

I expect that the project will take a few weeks … so much other stuff to do.

Furnace Re-refractored

Well, I’ve relined the flowerpot furnace and fixed the major cracks. I’ll be giving the furnace a firing next weekend to finish the curing of the refractory and see if it blows up (there may … will … be air pockets in the refractory).

I am also planning to get a start on the mulling machine today (time and weather permitting). It’s only 9 degrees C here in sunny Hobart today, and the less time I spend out in the workshop, the better.

I have a bunch of 3 litre glass bottles that I am going to turn to glass sand when I have the mulling machine finished (or even only partly finished) and I’ll line the furnace with a glaze as well.

Part of the steel drum that I’m using for the mulling machine will be used to make a new furnace, so that’s a good thing (woot!). The new furnace will be about 2’ high and about 2’ diameter with an internal diameter of about 1’ x 16” high. Being a steel drum means that I can weld a lid onto the furnace so that I can better manage the heat in the furnace. Pictures will be posted, when I’ve done more.

Green Sand

Well, I’ve mixed up some green sand for casting and it’s all packed away and ready to be used.

The mixture that I ended up using is:

• 3 parts sand
• 1 part fireclay
• 1 part water

The mix ratio for the water is a bit of guesswork, since I just kept adding water until the consistency was right. I’ll be including pictures of the greensand in later projects when I’m actually using it. Not much interest in some photos of sand!

The sand that I used was from an old bag of mortar that I had lying around. I hand sieved the sand to pick out the rocks and detritus, but it is generally a fine sharp sand with very few inclusions (although some of the inclusions were quite large).

I mixed the dry ingredients in a 30 litre sealable tub and then added the water. After mixing with my hands for a while, I sealed the tub and started to roll the mix around to better combine the contents.

When I was finished, I had a mix that wasn’t leaving much on my hands; formed a firm shape with pressure; and, broke cleanly into large clumps.

It probably needs a little more clay, but then again, it may not, so I am leaving it as is until I start casting.

Pewter Casting

Making stuff with molten metal is fun. I wanted to start playing with casting metal objects, mostly decorative stuff and the easiest way that I could see to start was with a low melt metal … such as pewter. I wanted to use a lead free pewter so I looked … and looked … and looked some more and found some at the local tip shop. Mostly old mugs and such that people have thrown away. The tip shop usually has some pieces, but be careful, most of the stuff marked “made in China” is lead based pewter. If it is marked as silver pewter, you are fairly safe.

Next I had to find some soapstone (steatite). I was able to source soapstone in small quantities from an art supplier.

Steatite is a soft stone that is used in making talcum powder, I was able to cut the stone using my bandsaw and then clean it up on my belt sander.

I wanted to carve the stone in as direct a fashion as possible … no power tools, so I picked up some very cheap carving tools from a discount shop.

Most of these tools are rarely used, I mostly use the straight edge and the narrow curved knife shown above.

I draw the basic design onto the soapstone first and then start carving. I find the carving to be very cathartic, and I can get lost in the process. The hardest thing about carving soapstone for making molds is remembering that to reverse the image. The bits that I want raised in the cast, are cut deeper, and the parts that are inset are raised in the carving. Also, using these tools I don’t have a very fine finish (probably because I haven’t practiced much). You can get good results if you work to your level of competence.

Here I have made a badge for some friends of mine who are medieval artillery enthusiasts.

I have notched the edges of the soapstone so that I can key the two parts of the mold. On the reverse face, I have carved a gate to allow the molten metal to enter the void.

I’ve also carved my initials into the back so that the badge ends up with my moniker.

To melt pewter, I use a simple and cheap portable gas (butane) stove and a stainless steel pot.

This gets the pewter from solid to liquid in about 10 minutes (depending on volume).

The two haves of the mold are clamped using a simple spring clamp and sit in a cooking tray.

When the metal is molten, it is carefully poured into the gate and, moments later, the object can be demolded. Some care should be taken because it is still going to be hot. Always take care when working with molten metal. If your mold gets wet at all … do not use it until it is completely dry. I once cast a metal figurine when there was a tiny amount of water in the mold. It exploded in my face when the water vaporised and I am very lucky to still have two eyes!

Rest the mold between castings as the steatite retains a lot of heat from the casting and can become too hot to use.

Here are some of my castings.

The badge needed to be cleaned up and there was too much air trapped. This needed more gating so that the gasses could escape. The carving was not crisp enough either, so I still had more work to do.

The nice thing about pewter casting is that you can melt and pour fairly quickly and remelt and repour. This means that you can refine your design fairly quickly.

When I made the button, I used a wet nylon scouring pad to smooth the inside of the mold. I was quite pleased with the result.

The above is an Anglo Nubian goat head that I cast. This is before I cleaned the casting up. The design went through a couple of alterations but essentially looks the same. To clean the design up more, I used a set of fine files (and a Dremmel). I made a pair of these along with a pair of prick eared goat pendants as giveaway’s for the goat club that I am a member of.

All up, the hobby is quite fun and gives you stuff that you can show off. The stove cost $15, the carving tools $2, a block of steatite (6” x 6” x 6”) was about $30 and the pewter has cost me, on average $5 per mug. I melt the mugs down as soon as I get them and make ingots by pouring the metal into a steel muffin tray.

A word of caution. Any molten metal is going to be very hot, it sticks to you and burns. You have to take care and wear safety gear at all times. Don’t play around with molten metal and if you are a kid … ask your parents for their help! Seriously, it really hurt when I had that figurine blow up in my face and I had to peel lead off my eyeball.

Furnace Tongs

I needed a decent set of furnace tongs that didn’t need to be forged (my forge isn’t set up yet). So I grabbed some flat stock, an angle grinder, my arc welder and some re-bar and got to work.

I built this set of furnace tongs so that I could easily get the crucible out of the furnace without turning to ash.

Basically, the tongs are a couple of lengths of steel re-bar welded to a couple of bits of angled steel.

The hinge in the middle is simply made from a welding a bit of flat stock in the middle of the re-bar so that I could pass a bolt through the middle.

Not terribly pretty, but the tongs work very well.

I needed to be able to position myself over the furnace and lower the tongs, grip the crucible (without crushing it) and then lift. I also wanted to give myself enough distance between my face and the furnace, so the tongs had to be long enough that I could do the whole thing standing up.

I still need to make a crucible cradle that I can use to hold the crucible and pour the molten metal into the flask. I can do that with the tongs, but it gets a little difficult … different design needed to do that.

Flowerpot Furnace

This is my first furnace. I have based the furnace design on the classic “Flowerpot” method described by Lionel Oliver on his excellent site (http://www.backyardmetalcasting.com/).

Basically, the furnace is a large terracotta pot that has been lined with a refractory. I searched online for a suitable mix and came up with 3 parts fire clay; 3 parts Portland cement; 1 part perlite. In retrospect, sand; Portland cement; fire clay and perlite would have been better … but … whatever.
I used a plastic flower pot to make the void in the middle where I will burn my fuel and a steel tube for the air intake.
I let the refractory cure for a week and then gave the furnace a test firing.

I dodgeyed up a connector for an old cheap vacuum cleaner for the fan and connected it to the furnace. The burn was pretty good. Initially, my crucible was a stainless steel pot that I bought from the tip shop. This gave me about half a kilo of aluminium, but the pot was a little thin, so it died after a few firings.

There are loads of resources out on the web for finding good recipes for refractory and cheap home-made furnaces. I suggest that you look far and wide and read as much as possible. Start small and have fun.

A View into Hades

The Flowerpot Furnace was my first smelting furnace. The melt in the furnace above is aluminium destined to become an unfortunate lump of ... aluminium. This was a pretty fun experiment and left me with the desire to melt stuff.

Since the first melt, I have indeed melted other stuff. including some old brass tap-ware. The furnace didn't like being cooled down rapidly in a Tasmanian downpour, however, so I need to repair my furnace.