I needed a vacuum chamber to remove the bubbles from liquid casting investment.I made it from a 10mm plate of aluminium and a thick glass mixing bowl.
Since the base would double up for vacuum casting (in which a casting flask sits on a heatproof silicone gasket and the glass dome isn't used) I needed the vent hole to be in the middle of the slab. I started by making a really long drill bit. I took an old 4mm drill bit, and ground the shank down to half thickness. I ground a corresponding flat on a length of steel rod, bound the two components together with fine steel wire, and laid the assembly in a piece of angle to hold them parallel.
I brazed them together with a MAPP torch. Here's the finished drill bit. It ended up beautifully straight, probably through more luck than judgement.
I drilled the plate sideways on the lathe, then drilled down from the top to meet the hole.
I machined this nozzle component to be a friction fit on a length of hose. It has a recess for an O-ring.
I drilled and tapped mounting holes either side of the vent hole.
I made a sealing gasket from adhesive-backed neoprene foam tape (Farnell 536805) . Can recommend that material for seals; did the job perfectly. Here's the whole setup with a ringing phone inside. When pumped down, it was inaudible.As a finishing touch I added some sticky rubber feet.
Here's the vacuum chamber being used to degas investment
Here it is being used in a vacuum casting attempt. My pump is too weedy and I never got a complete fill with this technique, so I eventually abandoned it for centrifugal casting.
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