My work is primitive as molding goes. I use the technique used by bullet molders, wherein the part is cast. the mold is opened over a pail of water, and the part literally falls out to be chilled. There is a "sprue cutter" built into the frame of the mold. As the part freezes in the mold quickly enough that by the time I move from the cast to the sprue cutter to opening the mold, the part, although quite hot, has frozen and is ready to be dropped into the chill bucket.
A "large" part with a multi-part mold would take longer to disassemble, I'm sure. The lead is cast from a "bottom tap" melting pot. Since I'm working in a "less than ideal" environment (my front steps), there (is)are several seconds from pouring the mold to despruing. It's sorta try it and if you move too fast, remelt the part and try slower next time. The lead does not adhere to the alum., although it will "catch" on a negative edge. Some taper is "thought in", although in my experience the lead shrinks away from the mold enough for small/ short cuts not to have any appreciable relief. Again, my parts are small and relatively simple. Something like the photo might well have a different result.
I use steel pins set into the mold as pilot holes for tapping. The mold "body" is aluminium. On my parts, there has never been a part that hangs, requiring "rapping". Bullet molders run their part through a "sizer" before loading, my parts are glued directly on the model, without even trimming. As noted above, chemically pure lead may have different results. I(for hardener), as well as bullet molders(cost), use recycled tire weights.
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