Posted by bruce paul fink on December 15, 1998 at 19:51:41:

originally posted by bpfink on June 17, 1998 at 07:25:11:

This vacuum chat has covered a lot of great areas with systems that should be helping anyone setting up or making one function to their liking.

So here are a few more thoughts from the files of firsthand use, youse abuse, and loose juice.

#1 On the lower level vacuum side: A common vacuum cleaner suction is a good thing also and is stronger than you might

imagine. Remember the bowling ball ads where one is picked up with a common looking (but specially designed ) funnel (with a great seal of the contact edge)?

A good vacuum cleaner if hooked up to a standard 55 gallon drum can suck the walls in and make it look like Mr. Bigheadman just finished his 8th beer and is stacking up the tally with crushed cans.

I bring this up since not all vacuum requirements need that kind of evacuation force for totally removing the bubbles in a casting mix be it molding rubber, investment or molten metal. Sometimes the requirement is just to make sure metal flows into a cavity with no pockets and then the quality vacuum is a lot less.

I have used a 55 Gallon drum with a fine screen baffle in the bottom and a sealed 3/4 inch copper pipe running up on the outside to fit to a vacuum line.

The drum is used like a sealed sand pit and the burned out / ready-to-pour-metal- into investment is placed in the drum with sand surrounding it everywhere.

The top seal of the surface is made by then mixing up some plaster and sealing the drum edge to the investment. (Or just clamp tape a layer of rubber sheeting over the drum for this step.)

When nearly set, pull a vacuum , this will suddenly show you how much space was left in the poorly tamped sand and it will drop sink. Re-pour a new plaster seal and let this set up. (All this is usually done while the crucible is melting it's load , for me about a 110 minute space since it is for about 300# bronze per melt.)

Now pour the metal and also put the vacuum on again (for a one man foundry this means kick the switch on or pull the lever with a string laying near the place you need to be. It's a

cute little choreographed kick / swish /look at me now / ho boy it worked again thing).

And why did the sides not buckle in this time , cause the thing was full silly. Ever try to hand crush a beer can when it's full and sealed?

#2 The old standard vacuum cleaner is also used as a table top holding clamp where I am doing a succession of similar machine routings for cleaning up or surface refining on cast metal forms, or polishing with a flexible shaft hand held wheel, or etc. (for me this has included doing a couple hundred small cast signs where the final edge had to be machined to a precise polish and the time element gets real boring unless it goes fast. Yah man, I

gotta do work that is less than preferred sometimes too). Also for holding any flat base side while grinding or working on other sections. It is just a real good clamp that has no surface parts and that can be put on and off with a switch flip.

#3 And one more point, if you have a great setup with a high vacuum but don't want to loose it for each suck level (say your pump is small, tank is large and you are just doing the holding thing or have a cut-off point where too much of a suck is detrimental or wasteful) there is also a vacuum level regulator that you can put on the line between your work piping and the holding tank. Don't know who sells them, the ones I have fit a 1 inch inlet and outlet so they are probably more for industrial levels but they are adjustable. Kind of like a gas regulator to

reduce pressure but in this case it is designed to hold back suction. If anyone is interested, I could part with a couple as a guy can only suck so much before he shows it.

#4 As for bell jars. When you want to be able to see the inner workings that's great, when the required sizes get too big for budget or locating, go to old cast aluminum pressure cookers which you can make work in reverse, go to upside down heavy kettles or thick wall steel tanks with one end smoothly cut off, go to many others that are probably lying around and then if a window is still needed cut a hole in it big enough to see through and put a thick (like 3/8 to 1/2 inch thick ) plexiglas window on it and seal with a good 1/2 inch or so edge of silicone caulking. Remember this is for a vacuum so the plexi is on the outside and a suction will only make the seal better. This system now means you can afford even large sized bell jar substitutes and a

whole new range of functions will loom ahead.

#5 Ho boy... gotta go play some more.

bpfink

90 Pole Bridge Rd

Woodstock, CT 06281 USA

http://www.fink.com/bpfink

http://www.artmetal.com/village/chat/main/transcrp/980129MN.htm

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