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Homemade vacuum table issues


#1

Hello everyone! I recently tried to make my own vacuum chamber using
a 2 -stage 3 cfm 25 micron vacuum pump. The base of where my bell
jar is sitting on is wood covered with a silicone sheet. I cut a hole
in the wood/silicone and have my vacuum tube sticking out of it. When
I put my bell jar on it I get good suction (I can’t separate the
belljar from the silicone) but I can’t boil water at all. What do you
think my problem is? Could it be the wooden base (most people say to
use a thick aluminum base)?

Is my pump too weak? I don’t have any vacuum leaks… Tomorrow I
should get a pressure gauge which should tell me how well the
suction is, but right now Im not sure what’s wrong. Any ideas? Thank
you! :slight_smile:


#2

The 2 -stage 3 cfm 25 micron vacuum pump you are using is fine, it
is very common and what lots of folks are using. The wood is porous
and “breaths” and will flex under pressure so it is not a suitable
material. Any thick metal plate or really thick plastic plate will
work.

John
The Jewelry Equipment Dr.


#3

Jane,

I recently tried to make my own vacuum chamber using a 2 -stage 3
cfm 25 micron vacuum pump. The base of where my bell jar is sitting
on is wood covered with a silicone sheet. 

The wood base reminds me of jokes about screen doors on submarines :slight_smile:

Aluminium, plexy or even glued formica would really help for the
base. Your pump sounds good, vac work really takes care of all the
little details. At the best of times it sucks big time :slight_smile:

jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand


#4

Ditch the wood base it is the source of your problems. You must use
something like steel or aluminum that is vacuum tight.

Jim

James Binnion
James Binnion Metal Arts


#5

Wood being porous is likely the suspect. I have built several vacuum
tables over the past 40 years and always used either steel or
aluminum. You must get a good seal from the rubber to the “table”.
And the table must be non porous. I have used mine with pumps as
large as 30cfm and as small as 1/3rd hp and even the small (far less
than one cfm methinks) will boil water in about a minute with a
fairly large bell. Try wetting first the underside of the silicone
and see if it improves… if it does then that seal is the culprit.
Even the wood where your hole is drilled will leak though. Also run
your thumb around the bell to see if it is clean all the way around.
I have also wetted this bell surface to check for a poor seal. You
can often see the leak on this one if its good and wet…tiny
bubbles.

Johnny