5. Mold halves in RTVfor badge body.
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6. Problem: Air-bubbles in RTV moulds. The uncured RTV had such a high viscosity, it needed a 29”mercury vacuum to de-gas it. My hand-pump only made 7”, so the fine detail [‘RÉGIE NATIONALE’] is a separate centrifuged graven plaque, making a 2-part badge assembly.
By careful mold design, mixing and pouring, bubbles can be minimised or kept off important surfaces.
Spincasting mould pattern laid up ready for pouring the RTV. Engraved master in brass.
Note ‘dummy’ casting opposite for balance and the ‘dirt pads’ -this is an old Alfred Herbert trick- dross and air are driven through the impression into a dead-end for a better casting.
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7. Spin-casting mold. I hand-cut the runners with a sharp blade, it’s easier than trying to mould them.
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8. Spincasting die, assembled and ready for mounting on the machine.
I dusted molds with talc; fine graphite powder is supposed to be superior. I raided the bathroom.
The discs are ‘Duralumin’, 4% copper aluminum-alloy, as strong as steel.
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9. Home made spincasting machine. 40 yr. old 230v 1Ø 1480rpm 4-pole motor, set vertical in oak frame.
Die fixes with a set-screw to the motor shaft. Note: motor is open-framed, hence the aluminum slot cover.
Cooling is not a problem; the motor only runs short bursts and has virtually no load.
Gives about 18 psi hydraulic pressure on metal at a 1” radius, equal to about a 4 ft head of metal.
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10. Machine fitted with ‘coffee can’ guard and running at speed. Concentricity is vital, so
accurate RTV mold and die parts were turned on the lathe.
Guard needed to be 1” higher than the header: Molten metal can eject up as well as out!
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[This message has been edited by pauluk (edited 11-10-2006).]

Wood work but can't!