Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe

On 6 Aug 2004 16:03:56 -0700, (Joe Emenaker) wrote:

Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe



sounds like the reverse of an air compressor switch....

I don't know what you're using for a vacuum pump but most pumps used to
evacuate a refrigeration unit can run for hours without any damage to
the pump. Are you trying to avoid too much pressure on the bag or too
low a pressure inside the bag? Why not just let it run? You might look
into a vacuum pressure regulator that would bleed air into the system at
a certain vacuum level. Most systems such as you describe have enough
leakage that a pump will short cycle unless you have a good sized reservoir.

rhg

wrote:

On 6 Aug 2004 16:03:56 -0700, (Joe Emenaker) wrote:


Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe




sounds like the reverse of an air compressor switch....

Joe Emenaker wrote:
Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe

That is the wrong way to do it. Most things like that have two switches
for an upper and lower limit. Let say your target is -7 psi. You would
set the lower switch for -7 psi and the upper switch at -11 psi. The
pump pumps until it is -11 and then quits. But it doesnt start back up
until it goes down to -7. Does this make sense?

-Jonathan

Somebody said it...reservoir. A tank (not all will take vacuum, might
collapse, will smooth things out a lot. A quart or so would probably make a
difference.
Wilson
"Joe Emenaker" wrote in message
om...
Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe

Cupla things Joe. First is that you need a switch with a greater ON-OFF
differential. That can be done with two switches, but many switches have an
adjustable differential and that would make things easy. Second, you can
lessen the surge effect by adding a reservoir. That could be any kind of
air tank, an old 20lb propane tank would work fine. You vacuum bag will
have very little volume, and thus is sensitive to surges from your pump.
The snubber tank will ease those surges and moving your switch away from the
pump and closer to the tank will help as well.

As for leaving your pump running all the time, that depends on your pump
design. Some will overheat if they are dead- headed. You need the specs on
your pump to know that. You can allow a bleeder valve to allow a little air
to flow all the time but that will also lower the vacuum level. A switch
would be better all around instead of running for 24 hours. I am very
interested in your project. How about some photos and more info when you
get it working?

--
Bill Pounds
http://www.billpounds.com/woodshop


"Joe Emenaker" wrote in message
om...
Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe

"Pounds on Wood" writes:

[...]

As for leaving your pump running all the time, that depends on your pump
design. Some will overheat if they are dead- headed. You need the specs on

Vacuum pumps? I have never seen any vacuum pump which was switched of
when the desired vacuum level was reached, they were kept running
until they broke down after a few years or the regular service
interval was reached. On the other hand, these were *real* vacuum
pumps, not just "air thinners".
And a plastic bag is a "huge leak" when it comes to vacuum
applications, let alone the wood inside and the glue with it's water.

--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23

You need a ballast chamber - a sealed rigid vessel connected into the
system, so that the total volume is much bigger. Assuming your leak is
small, this will allow far longer between the need to re-pump. Use
something like an old CO2 cylinder - a litre or two is usually
adequate..

It will take some extra time to pump the ballast chamber down, so you
might like to fit a valve onto the bag side of the circuit. Rather
than just plugging the pump into the bag and switching on, this lets
you pump the ballast chamber down first, then switch the vacuum
circuit.

You shouldn't need two switches. The effect described is called
hysteresis, and most air pressure switches should have some of this
built in.


--
Smert' spamionam

On Sat, 07 Aug 2004 15:58:33 +0200, Juergen Hannappel
wrote:

Vacuum pumps? I have never seen any vacuum pump which was switched of
when the desired vacuum level was reached,

That's because you're posting from a physics lab, with real pumps. If
you're using something like a Gast diaphram pump, or even worse an old
fridge compressor, then it's useful to switch it.

--
Smert' spamionam

A quart might smooth things out. A 20# propane cylinder (Bar B Que
tank) will smooth them out more and the things are available used cheap.
Also, a throw away cylinder used for refrigerant should be free from
your local air conditioning technician.

bob g.

Wilson wrote:

Somebody said it...reservoir. A tank (not all will take vacuum, might
collapse, will smooth things out a lot. A quart or so would probably make a
difference.
Wilson
"Joe Emenaker" wrote in message
om...

Okay... so I'm almost done with my home-made vacuum press. I was
surprised at how easy it was to make, actually.

Anyway, I've got my home-made bag, the pump, and pressure switch all
hooked up. As a test, I put my bathroom scale in the bag and turned on
the pump. The pump was starting to top out at 250 lbs on the scale
(and 100 sq. in. on the scale comes to a paltry 2.5 lbs/sq.in.), which
isn't fantastic... but, over the 2'x4' surface that I'm planning to
veneer, it's probably more clamping pressure than I could get with my
clamps.

Anyway, I'm going to start checking the bag for leaks and sealing the
vacuum connections better and then I hope to get up closer to 7-10
lbs/sq.in. We'll see.

My *problem* is this: I've got a pressure-actuated switch hooked up to
the system, with the notion that I can get the thing to pump down to a
certain vacuum and then shut off the pump... and then turn the pump
back on when a certain amount of air leaks back in.

In theory, it's great. In practice, it doesn't work so well. When I
start getting down to the target vacuum, each stroke of the vacuum
pump creates a momentary vacuum surge which triggers the vacuum
switch... which cuts the power to the pump for a moment, and the surge
subsides, and the vacuum switch turns back on, etc. What this sounds
like is like an engine running out of gas. The pump starts slowing
down... starts "running rough" (even though it's electrical) and just
keeps running slower and slower and never does get to the point where
it shuts off completely.

My plan, at this point, is to build a little electronic circuit which
will keep the pump going for a minute or so past the point where the
vacuum sensor first triggers, so that I'll get well past the trigger
point of the vacuum sensor. Then, the motor can shut off completely
and it won't turn back on until the vacuum drops to the point that the
sensor turns back on again.

Now, before I go and build this circuit, has anyone else made their
own vacuum press? If so, how did they get around this problem? Did you
just skip the vacuum switch and let the pump run constantly all night?
What does the real VacuPress do?

- Joe

What vacuum level we wanting here? I think somewhere around 29" will
provide all the clamping pressure you'd want. If you want to get down
into microns, two things to consider. A plastic bag probably isn't
going to seal well enough to achieve this kind of vacuum. I've spent a
lot of time chasing leaks and applying vacuum wax in a lyophylizer
circuit. Doesn't take much of a leak to keep you from getting water
evaporating levels of vacuum. If you want to dry the glue with the
vacuum you'd want a cold trap in the vacuum circuit like a commercial
lyophylizer, I'd think. My experience with vacuum is in refrigeration
and lyophylization so talking about a bag veneer press, I'm trying to
extend from experience to theory.

bob g.

Juergen Hannappel wrote:

"Pounds on Wood" writes:

[...]


As for leaving your pump running all the time, that depends on your pump
design. Some will overheat if they are dead- headed. You need the specs on


Vacuum pumps? I have never seen any vacuum pump which was switched of
when the desired vacuum level was reached, they were kept running
until they broke down after a few years or the regular service
interval was reached. On the other hand, these were *real* vacuum
pumps, not just "air thinners".
And a plastic bag is a "huge leak" when it comes to vacuum
applications, let alone the wood inside and the glue with it's water.

Remember, the most powerful vacuum pump imaginable with produce a
pressure differential between inside and outside your reservoir of about
15 psi.

bob g.

Andy Dingley wrote:

You need a ballast chamber - a sealed rigid vessel connected into the
system, so that the total volume is much bigger. Assuming your leak is
small, this will allow far longer between the need to re-pump. Use
something like an old CO2 cylinder - a litre or two is usually
adequate..

It will take some extra time to pump the ballast chamber down, so you
might like to fit a valve onto the bag side of the circuit. Rather
than just plugging the pump into the bag and switching on, this lets
you pump the ballast chamber down first, then switch the vacuum
circuit.

You shouldn't need two switches. The effect described is called
hysteresis, and most air pressure switches should have some of this
built in.

Robert Galloway wrote...
Remember, the most powerful vacuum pump imaginable with produce a
pressure differential between inside and outside your reservoir of about
15 psi.

....assuming the setup is located at or below sea level. Best I can get in
my shop is around 13.5 psi -- on a good day. Still, it's a helluva lot of
pressure for larger surface areas.

Cheers!

Jim

On Sat, 07 Aug 2004 11:55:45 -0500, Robert Galloway
wrote:

Remember, the most powerful vacuum pump imaginable with produce a
pressure differential between inside and outside your reservoir of about
15 psi.

bob g.


and that's at sea level. here at 2500 feet it'll be less...

"Pounds on Wood" wrote...
Cupla things Joe. First is that you need a switch with a greater ON-OFF
differential.

Right. The term I was going to use was "hysterisis", but I figured
that would make most readers' eyes glaze over.

That can be done with two switches,

Upon reading the specs for the switch I got, the company makes one
with two switches in it. Mine isn't one of them. Also, the switch is
bulky enough (about the size of a grapefruit) such that I don't want
to have two of them in this rig.

Second, you can
lessen the surge effect by adding a reservoir.

Thought of that, too.... but, like I said, I'm trying to keep the
bulkiness down.

As for leaving your pump running all the time, that depends on your pump
design.

My first try was with a 110V pump taken out of a FoodSaver, and it
would get pretty warm even after about a minute. My second pump, this
spiffy German 24V one (rated to something like .03 atmospheres) runs
much cooler. I might let it go for an hour and see how it does.

A switch
would be better all around instead of running for 24 hours.

Well, I've already designed the circuit and simulated it with a
circuit design program and it looks like it's going to work (and it
only uses about $20 of parts from Radio Shack). I might build it
anyway just for the nerd value. I'm concerned that I'll have enough
leakage into the bag, however, that the pump will end up running most
of the time, anyway.

I am very
interested in your project. How about some photos and more info when you
get it working?

Will do. When I have it working acceptably, I'll post the construction
details on my webpage where I have my home-made T-square fence.

- Joe

Lots of pressure on the veneer press. Not a lot to worry about when
considering what to use for the reservoir.

bob g.

Jim Wilson wrote:

Robert Galloway wrote...

Remember, the most powerful vacuum pump imaginable with produce a
pressure differential between inside and outside your reservoir of about
15 psi.


...assuming the setup is located at or below sea level. Best I can get in
my shop is around 13.5 psi -- on a good day. Still, it's a helluva lot of
pressure for larger surface areas.

Cheers!

Jim