Make a crucible
I have made a few steel crucibles now. The size I need is around 4" diameter x 6" deep. It holds about a half gallon. I have successfully melted aluminum and pure copper in them.
4" schedule 40 pipe has an inside diameter of a little over 4" and a wall thickness of .26". That makes it close to ideal for a crucible. I use a 7" piece of pipe and a 4" square of flat 1/4" steel plate for the bottom. I cut the piece of plate so that it fits inside the pipe and I bevel the edges of the pipe and the plate to get a weld that is as thick as the metal. That takes 2 or 3 passes using 3/16" welding rod. I use the thin rod becasue my machine only puts out about 60 amps and it's not really enough for a larger rod.
To make the piece of plate round and have it come out somewhat accutately, I draw a circle and then cut straight in up to the edges. Then I cut the small pieces off to leave the round. It does not have to be perfect. I try to leave small tabs on so that I can hammer it into the pipe so that it will stay while I tack weld it.
I have assembled the two pieces. You can see that there are gaps between them. That's no problem.
This is after the first welding pass after chipping and scrubbing. You cannot really see it but the weld is actually below the surface of the piece. It need another pass or two. You can just see weld metal on the inside of the pot. I tried to take a pic of that but it did not really turn out.
Here is the crucible after the last pass. I had to grind out several pinholes, but I am quite happy with the end result. I am going to leave it rough and not gring it smooth. I don't think that it would improve the actual quality at all. It would look nicer.
I have not had one of these fail yet. I have more than 10 aluminum heats on a large one made from 6" pipe. I have 3 copper heats on one like this made from 4" pipe. I like the 4" pipe better. The 6" pipe makes a very heavy crucible. Since I usually work alone when pouring, a smaller crucible is safer.
Here is a picture of me lifting the crucible out of the furnace with some tongs that I made. You can see the pouring shank that I made on the ground next to my feet. It makes pouring a joy and a heck of a lot safer.
Here is a picture of the pouring shank with a crucible in it. It holds a full curcible very securely.