vacuum base for bell jar
 

OK, I got a vacuum pump and I found a 1/2 gallon bell jaw at Fisher
for $42. I didn't see a base so I am wondering about making one.

I figure an aluminum plate would work fine. How thick of a plate
do I need for a 1/2 gallon bell jar? Is 3/8 enough or do I need
to go to 1/2 ?

thanks
chuck

On 16 May 2005 21:40:41 GMT, (Chuck
Sherwood) wrote:

OK, I got a vacuum pump and I found a 1/2 gallon bell jaw at Fisher
for $42. I didn't see a base so I am wondering about making one.

I figure an aluminum plate would work fine. How thick of a plate
do I need for a 1/2 gallon bell jar? Is 3/8 enough or do I need
to go to 1/2 ?

thanks
chuck

If the 3/8 plate sucks up into the bell jar.....go to 1/2"

I should think the .375 would do the job.

"Chuck Sherwood" wrote: (clip) How thick of a plate do I need for a 1/2
gallon bell jar? (clip)
^^^^^^^^^^^^^
Depends. If the bell jar is an inch in diameter and several feet tall, the
aluminum plate would have to support only 11.5 lb, so it could be pretty
thin G.

If the 3/8 plate sucks up into the bell jar.....go to 1/2"

I should think the .375 would do the job.

Thus, the birth of vacuum forming!

In article , Leo
Lichtman says...

... If the bell jar is an inch in diameter and several feet tall, the
aluminum plate would have to support only 11.5 lb, so it could be pretty
thin G.

But if it were a foot in diameter, then the force at the
center of the plate would be about 1600 pounds or so. The
height of the jar does not matter.

FWIW a commercial system might have a one foot dia bell jar
and a half inch thick stainless baseplate. The baseplate
has to be rigid enough to not oilcan excessively, because
the innards of the thing being pumped down are bolted to
it.

Jim


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"jim rozen" wrote: But if it were a foot in diameter, then the force at
the center of the plate would be about 1600 pounds or so. The height of the
jar does not matter. (clip)
^^^^^^^^^^^^
We're just kidding around, aren't we? So. I will point out that the OP
specified that the bell jar is about 1/2 gallon. So, if it is a foot in
diameter, it will be about 2" tall. Your force calculation gets the correct
number, but the force will not be at the *center* of the base--it will be
uniformly distributed over the entire area.

The only point I was trying to make in my facetious posting was that the
required thickness of the base cannot be specified unless the diameter is
known.

As a practical matter, a 1/2 gallon bell jar is probably about 6" in
diameter, so it will have a force on it of about 400 lb. I would make the
base out of whatever is available in the range of 1/4" to 3/4", just based
on two things: 1.) You don't want it to "oilcan". 2.) You don't want it
to be too heavy to handle easily.

In article ,
Errol Groff wrote:
On 16 May 2005 21:40:41 GMT, (Chuck
Sherwood) wrote:

OK, I got a vacuum pump and I found a 1/2 gallon bell jaw at Fisher
for $42. I didn't see a base so I am wondering about making one.

I figure an aluminum plate would work fine. How thick of a plate
do I need for a 1/2 gallon bell jar? Is 3/8 enough or do I need
to go to 1/2 ?

[ ... ]

If the 3/8 plate sucks up into the bell jar.....go to 1/2"

Be *sure* to put that bell jar in a steel wire cage to catch the
particles if the base deforms and induces failure in the bell jar.

I should think the .375 would do the job.

IIRC, the vacuum system that I used at work some years ago had a
base of about 1" thick steel. The bell jar was about a 12" ID, IIRC.
Yours sounds significantly smaller, but I think that I would avoid
aluminum, and go for steel. And in *any* case, I would require the
steel wire cage around the bell jar for safety.

Good Luck,
DoN.

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Chuck Sherwood wrote:
OK, I got a vacuum pump and I found a 1/2 gallon bell jaw at Fisher
for $42. I didn't see a base so I am wondering about making one.

I figure an aluminum plate would work fine. How thick of a plate
do I need for a 1/2 gallon bell jar? Is 3/8 enough or do I need
to go to 1/2 ?

I'd go with steel of 1/2" or thicker simply because I've never seen the base of a bell jar made out of anythign that wasn't thick steel. Al might flex and break your seal or chip the bell jar.

In article , Leo
Lichtman says...

Your force calculation gets the correct
number, but the force will not be at the *center* of the base--it will be
uniformly distributed over the entire area.

Quite right, of course. I quite the entire force number often
because it impresses folks, and makes them respect bell jars
a bit more. The idea that it's a glass jar with two tons of
force involved somewhere in there makes it easier to convince
them that it has to be covered in wire mesh.

The only point I was trying to make in my facetious posting was that the
required thickness of the base cannot be specified unless the diameter is
known.

Ah, got it!

As a practical matter, a 1/2 gallon bell jar is probably about 6" in
diameter, so it will have a force on it of about 400 lb. I would make the
base out of whatever is available in the range of 1/4" to 3/4", just based
on two things: 1.) You don't want it to "oilcan". 2.) You don't want it
to be too heavy to handle easily.

Sounds good to me.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

OK, I got a vacuum pump and I found a 1/2 gallon bell jaw at Fisher
for $42. I didn't see a base so I am wondering about making one.

FYI, the bell jar is 6-7 inchs in diameter.
thanks for the input. I will find some think plate.

A 6" diameter disc of aluminum .25" thick, simply supported around the
edge, with 415 lbs uniformly distributed over the disc, will see a
bending stress of 2620 psi and will deflect 0.005" in the center.
(Engineering Power Tools to the rescue :-).) 0.25" steel would deflect
0.0018", and 0.5" thick aluminum 0.0007".

--
Regards,
Carl Ijames carl.ijames at verizon.net

Chuck Sherwood wrote:
OK, I got a vacuum pump and I found a 1/2 gallon bell jaw at Fisher
for $42. I didn't see a base so I am wondering about making one.

I figure an aluminum plate would work fine. How thick of a plate
do I need for a 1/2 gallon bell jar? Is 3/8 enough or do I need
to go to 1/2 ?

thanks
chuck
Why not just go with a dessicator bowl instead? That way you get the
bowl, the lid, the method of sealing them together and the method for
connecting it to your vaccuum pump. A half gallon size is pretty
small. If you can get bigger, do it.


Pete Stanaitis

----------------------------------

A 6" diameter disc of aluminum .25" thick, simply supported around the
edge, with 415 lbs uniformly distributed over the disc, will see a
bending stress of 2620 psi and will deflect 0.005" in the center.
(Engineering Power Tools to the rescue :-).) 0.25" steel would deflect
0.0018", and 0.5" thick aluminum 0.0007".

Wow, Look like 1/2 inch aluminum (or steel) is the right choice.

Why not just go with a dessicator bowl instead?

Didn't know it was an option!

Chuck Sherwood wrote:
Why not just go with a dessicator bowl instead?


Didn't know it was an option!


Sorry, my spelling ability failed me. It's desiccator. Search for
"desiccator bowl" to get started. I found 4 or 5 hits.

Takes me back to the 60s thru the 80s when I worked in High vacuum
technology.

Pete Stanaitis

Takes me back to the 60s thru the 80s when I worked in High vacuum
technology.

I have been following ebay sales of vacuum pumps.
I noticed this bidder "mmetropolis" buys lots of
vacuum pumps and some pretty big ticket items too.
Makes me wonder what he is doing with them?

chuck