Using the Lathe to Clean Up Your Castings
Casting metals is a lot of work but with rewarding result. You foundry buffs know that clean up is a large part of the work, especially if you are going for precision geometrics. But master craft, James, let me in on a way to use the lathe for clean up that yeilded a quick, consistent finish.
Allow me to give a word of appropriate warning. The lathe can be one of the most dangerous pieces of equipment in the shop. Use with adequate training and healthy fear. In general, I'm highly cautious of things that spin.
Our team started with a 3D printed model from an engineering print. From there master sculptor Josh made our
silicone molds copying the image into wax. We experimented with the sprews because the thinness of the wall gave us problems with the metal cooling during the pour, leaving inconsistent flow on the bottom side. The waxes were coated over weeks in ceramic shell and then flash fired out in a kiln at around 2000 degrees. The pour went well, resulting in a nice brass cast.
I then cut the sprews away using an angle grinder, chipping
the remaining shell away with hammer and chisel. A 4" belt sander and 5" orbital leveled out the sprews and vents. So far so good, but now the job of taking the finish down to a fine consistent smooth (and even) model.
This is where James stepped in and placed the piece on a lathe. This is actually a wood lathe modified for metal
work. A wooden mandrel used for spins was placed in the large end a block of shaped acrylic in the smaller to lock the bell in
place. He's demonstrating in the pict below how on relatively slow speed, a file over the surface quickly clears
away the rough outer layer. After that, sand paper finished the work, beginning with 80 grit taking the piece down to 220 sufficient for our craftsman to fit the piece into the finished custom form.
Below is the complete brass, ready for patination.
