I needed a 1.25″ by 1.25″ by 1.25″ chunk of brass to mill a bridge for the Stroh violin that I am working on for a friend. Unfortunately, my local supplier of cut-offs and odd ends of non-ferrous metals has closed. I could have ordered some brass from McMaster Carr, but I have so much scrap brass kicking around that I thought I’d cast some. Of course all I’ve done to date is melt scrap aluminum into ingots so I needed to make some tools first, namely a pair of tongs to handle the clay-graphite crucible I’d need for the brass and a rammer for the sand molds.
I modelling the rammer in Autodesk’s 123D Design and then printed it on my RepRap Prusa Mendel. This is close to the largest thing I’ve ever printed and I had to split it up to fit on the print bed.
The finished print fit together nicely.
Since I did not want to print a second half of the rammer pattern–it took 7 hours!–I CNC’d plywood faces for the cope and drag as well as the pattern board, this allowed me to pack the two halves of the mold separately, yet still maintain a high degree of accuracy. I was quite pleased with this technique for making the mold and I will likely use it again.
This is not as crazy as it looks! It’s cold outside so I needed to heat the propane tank to get it to produce gas quickly enough for my furnace. I’m told that putting the tank in a tub of hot water is even more effective so I will try that next time.
That’s about ten pounds of aluminum melted from old hard-drive chassis, the rammer used about 7 pounds of it.
The finished rammer!
To melt the brass I needed a crucible, ordered from Budget Casting Supply and tongs to handle it. I welded these up from some steel bar-stock and black iron pipe. Note the stop bolt to prevent the tongs from closing too tightly on the crucible.
The crucible also need to be conditioned before the pour. I set mine over night on a warming plate that kept it at about 210 degrees Fahrenheit and then fired it to red heat, letting it cool overnight in the closed furnace.
The brass pour went smoothly thought the green-yellow glowing zinc vapors were kind of scary! I never smelled the sickly-sweet smell of burning zinc, but I will be sure to wear a remote air source mast the next time I do a melt.