There I was, Friday afternoon, badly in need of 3-way gas connector for my propane set-up. One regulator - needed to run two torches. Maybe I could braze one up? A quick search of the workshop for a bit of 1/4 inch pipe soon put paid to that. Nothing to be found. So, stuck for the week-end? Not yet
Could I cast one? I had couple of drinking straws that would give me somewhere near the needed out-side diameter, plenty of wax and my little RT casting system. (see Reid Technique)
But the internal passages to carry the gas? They were going to be tricky. Drill them into the cast metal? With just a battery-powered hand drill, that wasn't going to easy. Drill into the wax and try to core them? Impossible . Premake the cores in ceramic? At about 1 mm, forget it.
That's when I spied the old pencil. The blacklead core was just the right size. But would it take the molten metal? Damn good chance since it's mainly graphite. Oxidation? With my reducing first coat, it should survive. Strong enough? Seemed so. Getting it out? Should be soft enough to drill easily. All we can do is try.
So, out with the paring knife, and in a few minutes, I had several bits of lead, one of which was long enough to span two arms of the three-way and another that would do for the third. But they have to be joined somehow with a substance that won't burn away in the mould. Glue? No. Ceramic? Maybe.
Tne problem seemed solved with a bit of barbeque charcoal. It cuts quite nicely with a fine tooth saw. A small cube, about 4mm on edge was drilled slightly undersize and the pencil lead pushed in to form a T-joint, a drop of wax holding it all together. Pieces of drinking straw were slipped over the rods, leaving a little of these exposed at the ends to be grabbed by the investing shell as core prints. Wax was then used to fill the hollow straws and to paint over the charcoal block to the thickness required to be cast in metal. It was ready for spruing.
Four coats of ceramic shell slurry were applied drying with a hair-dryer in between and, a couple of hours later, the piece was blasted with a flame to remove to wax and plastic straw. Searching about the studio for some casting metal, I came across some scraps of silver , and decided these would do rather than bronze. We're hardly talking economics here when we consider the time spent.
Twenty minutes later, the piece was cast using my inversion method. The graphite proved surprisingly easy to drill out, the drill-bit following the hole with no drifting. A bit of filing to taper off the ends, and the piece was fitted to the hoses. A quick test with soapy water and we were in action.
So there we have it - a rather expensive t-junction, but more importantly, a sweet solution to 'long-hole' core casting.
Hope it can be of use to you.
