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Investing vacuum casting problems

I hope some one in the vast assembly of Orchid members can explain
what happened to my casting today.

But first a little history.

I have cast only on Thursday and Friday for the last 20 or so years.
My wife says I am too much a creature of habit. So today I decided to
break the mold and cast on Wednesday and Thursday. Was the problem I
had today a sign from the casting guardians telling me that I should
remain a creature of habit and cast only on Thursday and Friday?

Were the casting guardians not happy with the designs on the things
I wanted to cast today so they caused this weird problem hoping the
items would never be cast?

The problem:

I planned on investing 18 2 1/2 inch flasks. I vacuum on a table
similar to Rio"s vacuum table. It is a flat inch aluminum plate
mounted on springs to a base with a vacuum gage and a valve. Early
this morning I check to insure my mixer and vacuum pump work. So far
so good. Being a creature of habit I mix 5 pounds of investment. That
should be enough to pour around 7 or 8 flasks

The mixing goes well. I put my rubber mixing bowl on the rubber pad
on the vacuum plate, put my bell jar over the bowl and shut the
valve. No vacuum in the bell jar. Remove the bell jar and put a
finger over the vacuum tube that leads from the bell jar to the
vacuum pump. A vacuum. Back on with the bell jar. No vacuum. Remove
that bell jar and go to the backup bell jar I have. No vacuum. By
this time the mixed investment is starting to set so I dump it and
clean up.

I Live in Phoenix and cast outside. Today the temperature of 112
degrees is not conducive for one to keep his cool.

Now I have time to figure what the problem is. The pump is pulling a
vacuum of around 26 inches without the bell jar but not in the bell
jar. What the heck is the problem?

I changed rubber pads. Still no vacuum.

I wet the bottom edge of the bell jar and place it on the rubber
pad. I notice the vacuum is pulling bubbles from underneath one side
of the bell jar. Rotate the bell jar and the same area is bubbling.

Could it be the inch aluminum plate is no longer flat? Sure enough
the plate has a dip of about 1/32 inch on one side.

How did the plate become warped. Have any of your ever had that
problem? The plate is about 10 years old. I do cast 6" flasks that
have 5 pounds of investment in a flask the weigh several pounds. Is
it possible the heat and weigh of such a large flask has caused the
plate to bend down?

You may ask what happened to the investing. Thank goodness I am a
pack rat. I had an old aluminum vacuum plate I saved from an old
vacuum system I had. And who says it is not good to be a pack rat?

The investment went well with the new plate.

Tomorrow I will determine if the design guardians dislike my design.
If they don"t like the designs today will be for naught.

Lee Epperson


Methinks you didn’t sacrifice to the casting gods before starting
the process. They do tend to get problematic if they don’t feel
respected enough :-).

Seriously, though - could something have gotten dropped onto the
table? I seriously doubt that the large flasks would have caused
warping of the plate unless the plate is REALLY thin - we use the
large flasks all the time in the studio and have been using the same
aluminum plate for close to 20 years with no problem. (Hope I haven’t
just jinxed that!)

The other alternative might be to use a thicker and "squishier"
rubber pad that will account for the ding in the plate…

It’s always such fun trying to figure these things out isn’t it!

Karen Goeller
No Limitations Designs
Hand-made, one-of-a-kind jewelry

There’s no way a 1 inch thick AL plate would become bent from a 5lb
flask, even a very hot 5 lb flask. The silicone gasket prevents most
of the heat from transferring through anyway, even with multiple

Is it mounted on springs or a rigid frame? The only thing I can think
of, if it’s mounted on a rigid frame with absolutely no way for it to
move and then sits out in the sun on your hot 112 degree days,
thermal expansion might warp it.


Well Karen, the casting gods seemed to be pleases with my offerings
today as I had no problems pouring the metal today. The 112 degree
weather didn’t help but I managed to get most of the stuff done
before needing a cool shower. The items in 18 flasks seemed to look
clean and fine in detail. I vacuumed the flasks on the warped
aluminum plate without any hitches. The warped section of the plate
is on one side only not in the center.

It would be very difficult to sprue lots of my designs in a large
flask as I usually cast so many different sizes and shapes of items.
This casting included three small pots, a bunch of ranger buckles,
some earrings, several big rings and some pendants.

Harry, the warped 1/4 inch plate is mounted on springs. The
equipment is stored in cabinets when not in use. The plate is never
loaded except for when I use it for vacuuming investment and molds.
How it was warped is a puzzle I may never solve.

Lee Epperson