Post by thread:[EE:] Home vacuum-forming

'[EE:] Home vacuum-forming'

Somebody mentioned here a while ago that they were doing or

trying this. I was daydreaming about a couple of small cases I

need and suddenly realised I've got everything I need to make

them. Oven - vacuum pump - acrylic sheet - ability to make

a mold. Will be Googling around but if anyone has helpful hints

that would be appreciated

TIA

===============================================

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Um...the guy who makes one of the PCB transfer films has some info. I

think the website is http://www.dynaart.com though I could be wrong,

and I don't have time to check at the moment. Vacuum forming info will

likely be found on model making sites, though there should be some

good info on theatre prop sites as well.

Never tried it myself, please post pictures if you do it...I wanna see!

Josh

-- 

A common mistake that people make when trying to design something

completely foolproof is to underestimate the ingenuity of complete

fools.

        -Douglas Adams

On Tue, 14 Sep 2004 11:32:05 +1200, Jinx <spam_OUTjoecolquittTakeThisOuTclear.net.nz> wrote:

> Somebody mentioned here a while ago that they were doing or

> trying this. I was daydreaming about a couple of small cases I

> need and suddenly realised I've got everything I need to make

> them. Oven - vacuum pump - acrylic sheet - ability to make

> a mold. Will be Googling around but if anyone has helpful hints

> that would be appreciated

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At 11:32 AM 9/14/2004 +1200, you wrote:

>Somebody mentioned here a while ago that they were doing or

>trying this. I was daydreaming about a couple of small cases I

>need and suddenly realised I've got everything I need to make

>them. Oven - vacuum pump - acrylic sheet - ability to make

>a mold. Will be Googling around but if anyone has helpful hints

>that would be appreciated

There are some people selling plans that you can find by googling.

I think Gingery/Lindsay Books has something on this for a reasonable

price.. yes, here it is:

http://www.lindsaybks.com/dgjp/djgbk/vacf/index.html

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"

.....speffKILLspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com

Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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On Sep 13, 2004, at 7:55 PM, Spehro Pefhany wrote:

>> Somebody mentioned here a while ago that they were doing or

>> trying this.

I sorta want to vaccuform old CDs.  (Or for that matter, new CDs.)

Nice colors available, thin, strong Polycarbonate, etc.

Does anyone know if this is workable?

BillW

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> Nice colors available, thin, strong Polycarbonate, etc.

> 

> Does anyone know if this is workable?

According to the web, softening point for acrylic sheet is ~115C

(240F) and ~160C (320F) for polycarbonate, which would be

easy to reach in a domestic oven. Recommended working temp

for acrylic seems to be > 280F, so maybe 360F for polycarbonate

I'd put a CD in the oven and see what happens. Could be the answer

as to what to do with a pile of old CDs I've got. Thinking of cutting

them up to make mosaics or mirror balls, molding them would be nice

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www.hhhh.org/~joeboy/resources/vacuumtable/vacuumtable.html

You mean like this :)))))))))))) Found using the subject line as search in

google.

>Oven

- don't tell the wife it is fish and chips instead of roast tonight :)

>vacuum pump

You can't do the house work tonight, the equipment is being used elsewhere

acrylic sheet

What do you mean, where is the window, it is a hole there in the wall, just

like it always has been :))

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>I'd put a CD in the oven and see what happens. Could

>be the answer as to what to do with a pile of old CDs

>I've got. Thinking of cutting them up to make mosaics

>or mirror balls, molding them would be nice

Roman Blacks diffraction grating was another scheme for them. But I would

have thought that Jinx would have an enterprising business in his back yard

doing a clay pigeon shoot with them, like my favourite TV advert.

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> http://www.hhhh.org/~joeboy/resources/vacuumtable/vacuumtable.html

>

> You mean like this :)))))))))))) Found using the subject line as search in

> google.

joeboy eh ? Gotta be a sign (like betting on You Can't Lose at the races)

I did see warmplastic's site earlier. Came out first hit Googling for

vacuum forming. Looks easy enough. My only little concern is what

to do with all the offcuts, hate wastage like that

> >Oven

>

> - don't tell the wife it is fish and chips instead of roast tonight :)

You have cooked meals ? So rich, so rich.....

> >vacuum pump

>

> You can't do the house work tonight, the equipment is being used

> elsewhere

What is this "house work equipment" you speak of ? ;-)

> acrylic sheet

>

> What do you mean, where is the window, it is a hole there in the wall,

> just like it always has been :))

Saves on Windex I suppose

Actually, the sheeting (a lot of it too) I have came from next door.

Shhhhh. Long story short - when the land and house next door was

sold to developers it was discovered that the enclosed patio added

was illegal. Builders pulled it down and were going to burn the lot. So

I ended up with a great and very useful pile of decking timber and 3mm

acrylic

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> Roman Blacks diffraction grating was another scheme for them

Sounds a bit too much like science for me. I'll have a look into

it though, see if it could be made into entertainment for the lower

classes somehow

> But I would have thought that Jinx would have an enterprising

> business in his back yard doing a clay pigeon shoot with them,

> like my favourite TV advert

Oh, I'm not the dangerous gun nut out West. Tell'em Russell

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> Oh, I'm not the dangerous gun nut out West. Tell'em Russell

As long as you tell them that I'm not the dangerous rocket nut out west.

        RM

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On Tue, 14 Sep 2004, Alan B. Pearce wrote:

>> I'd put a CD in the oven and see what happens. Could

>> be the answer as to what to do with a pile of old CDs

>> I've got. Thinking of cutting them up to make mosaics

>> or mirror balls, molding them would be nice

>

> Roman Blacks diffraction grating was another scheme for them. But I would

Actually the diffraction grating was my idea I think.

Peter

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On Tue, 14 Sep 2004, Jinx wrote:

>> Roman Blacks diffraction grating was another scheme for them

>

> Sounds a bit too much like science for me. I'll have a look into

> it though, see if it could be made into entertainment for the lower

> classes somehow

I came up with a spectrum analyzer based on a diffraction grating made 

from a sliver of cdrom and a black 35mm film can. It must be in the 

archives. I still have one. I use it to test FL lamps. The ones that 

generate continuous spectrum and the ones that create headaches and single 

lines (and terrible color reproduction) can be readily told apart in the 

shop where they are sold ;-) If the archive cannot turn that up I'll 

repost this (assuming I still have it).

Peter

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That looks like a 'build-it-yourself' version of the out-of-the-box

solution here: http://www.warmplastic.com/how.html

But when does anyone want anything out-of-the-box? Isn't it more fun to

spend endless nights burning out your partners vacuum cleaner all the

while cursing sore hammer-broken fingers? Hm..

It's interesting to see how these 'home-brew' devices compare to

industry standard formers. Check this link for QuickTime videos of how

it's done. www.crclarke.co.uk/Pages/English/contact.html

Eee-by-gum! It's moved on an awful lot with all the new automatic

intervention! I wonder if the 'home-brew' version could be modified to

be 100% automatic with an old grill heating element, several motors,

switches, relays, LCD and our old friend, (of course), the PIC. :)

Cheers,

Stuart

http://www.psirens.co.uk

{Original Message removed}
I have forgotten who posted earlier but they referred to a book "The Prop

Builders Molding and Casting Handbook" by Thurston James. I bought the book

from Amazon.com (it was not expensive like the techie stuff) and read it.

Only the last chapter deals with vacuum forming and that on a grand scale.

Like making tile roofs for movie sets. Very interesting though. The earlier

parts of the book renewed my interest in fiberglass casting so I have been

off on that tangent lately.

BTW, the hard parts of vacuum forming seem to be the matter of an oven big

enough for the work and creating a vacuum source (or is it sink?) with

enough volume to draw down the material before the material cools out of the

plastic condition...

A home vacuum cleaner arrangement is not really up to the task. Besides, my

earlier experiments with home vacuums lead me to believe a lot of air FLOW

is essential to avoid toasting the motors.

John Ferrell

http://DixieNC.US

{Original Message removed}
At 04:32 PM 13/09/2004, you wrote:

>Somebody mentioned here a while ago that they were doing or

>trying this. I was daydreaming about a couple of small cases I

>need and suddenly realised I've got everything I need to make

>them. Oven - vacuum pump - acrylic sheet - ability to make

>a mold. Will be Googling around but if anyone has helpful hints

>that would be appreciated

>

>TIA

I've been doing small domes and such for lights for about a year

using a shop vac, a toaster oven and homemade plywood vac box.

Lots of little tricks to learn so where do you want to start ;-]

Dave

Psst wanna buy some funny shaped plastic scraps?????

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> Lots of little tricks to learn so where do you want to start ;-]

> 

> Dave

A little involved with something right now but rest assured I

will be aksing you things ASAP

> Psst wanna buy some funny shaped plastic scraps?????

Swap you for some dead chips........

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>> Roman Blacks diffraction grating was another scheme for them. But I would

>

>Actually the diffraction grating was my idea I think.

Oh, was it? I am sorry to attribute it to the wrong person. My apologies to

Peter.

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> I came up with a spectrum analyzer based on a diffraction grating made

> from a sliver of cdrom and a black 35mm film can. It must be in the

> archives. ...

> If the archive cannot turn that up I'll repost this (assuming I still have

it).

You mean this (from my archives :-) ) October 2000

        RM

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From: Peter L. Peres <plpKILLspamACTCOM.CO.IL>

To: .....PICLISTKILLspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU>

Subject:      [OT]: Found! Use for all your AOL diffraction gratings

Date: Tuesday, 17 October 2000 08:02

Hi,

I have discovered that CDROMs split in a certain way make excellent (at

the $0 level) diffraction gratings with lots of amateur uses, like color

separation in projects involving optics and analyzing various materials

and light sources.

Recipe to make a very simple and useful optical (light) spectrum analyzer:

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

(in about 15 minutes):

What you need:

1 CDROM (must be silver aluminium type, not CDR or CDRW).

2 opaque, empty 35mm film cans

1 Xacto knife

some duct tape (black)

Serves one per pair of film cans, up to 10 per CDROM.

Procedure:

1. Using an X-acto knife cut two almost parallel radial lines from the

inner hole to the outer rim of the CD, about 8 mm (1/3") apart, then snap

the CDROM between your fingers to obtain a sliver. Cut and snap again to

obtain a shorter sliver that fits forced into the inner diameter an empty

35mm film can (black or aluminium please). Take the part of the sliver

that used to be at the outer rim of the CD. This is the diffraction

grating. The more parallel the sliver to an actual radius of the deceased

CDROM the better (take your time to cut precisely).

2. Using the same X-acto knife cut a slot in the first opaque film

canister. The slot should be 5-6 mm (1/4") wide and go all the way from

the upper (open end) rim to the lower rim of the canister, and straight.

3. Using the knife, cut a straight slit in the remaining (other) empty

file canister, at about its center (of the closed end), so the slit is

about 1/3 of the diameter of the canister and centered. This is the slit

(optical aperture). Take some abrasive paper, make a strip of it that fits

in the slit, and work the slit edges until they are as straight and clean

as possible but do not widen the slit (check against light). My slit was

of about 0.2mm (in plastic canister).

4. Insert the sliver of diffraction grating into the lengthwise cut film

can, shiny (not label) face towards you, and press it down so it lies at

the bottom of the can as level as possible, and aligned with the

lengthwise cut (slot) so you can see all of it through the slot. Some hot

stuff helps to keep it in place.

5. Assemble the film canister with the slit with the one with the grating,

open end to open end, using black duct tape. Make sure that the slit is

perpendicular (at 90 degrees) with the sliver of CDROM lying at the bottom

of the other film can. You can improve the angle by looking at the image

of the slit on the grating while assembling.

6. Test your optical spectral analyzer instrument by pointing the slit

towards a light source (desk type low power fluorescent lamps work best,

they have a few very sharp spectral lines). Look through the slot at the

CDROM sliver and adjust your angle (keep the instrument steady with the

slit towards the lamp and move your head) until you see the spectral

lines. The first order lines appear at about 20 degrees from the axis of

the instrument and the second order are also very well visible (and better

spaced out) at about 40 degrees. The separation achieved is imho amazing

for such a simple instrument and I was able to see some very 'blue' lines

from an UV lamp (do not try this) so the polycarbonate passes UV

apparently. Also IR (this is guaranteed, the original CDROM readout laser

uses near IR).

7. Improvements: Increase the amount of light as much as possible using a

lens. The lens should focus a light source directly on the slit (outside

it). Adding a small piece of translucent paper directly on top of the slit

(outside) also improves the image. The slit can be replaced with one cut

in a thin aluminium sheet for much better precision. Install an eyepiece

to be able to view the spectral lines more comfortably. Install a

calibrated scale. I have tried a color TV camera, and the colors look

great. Although the CCD color filter probably cheats big time about the

actual colors in despite of locked white balance.

8. Uses: Use as color filter with lamps, LEDs, 'homebrew' color sensitive

detectors and many more uses. Teach kids about light spectra (do you have

any idea how much a decent prism costs ? Let alone one that covers UV to

near IR).

9. Question: What is the pitch of the tracks on a normal CD ? I am unable

to find this information (it is of about 2 um but how much exactly?).

sorry for the long post (but others posted longer and worse ones <g>),

Peter

PS; An now you have an excuse to split those spare CDROMs at every

occasion ;-)

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>BTW, the hard parts of vacuum forming seem to be the matter of an oven big

>enough for the work and creating a vacuum source (or is it sink?) with

>enough volume to draw down the material before the material cools out of the

>plastic condition...

Hi 

I've watched vacuum forming done, and it was a very simple set-up. They

were forming polystyrene(not foam!)

The positive/pattern was simple wood fabrications, and there was no oven,

rather a big element and a few fans blowing the air down. I think the

vacuum part was just an industrial blower, as a sucker.

The force required will depend on the temperature, depth of draw required,

thickness of sheet, resolution of pattern. Although a nice convoluted

surface can be obtained, the edges always pose a problem, same with

fibreglass moulds. Trimming them to an exact size, and polishing to hide

the work, is almost impossible.

>A home vacuum cleaner arrangement is not really up to the task. Besides, my

>earlier experiments with home vacuums lead me to believe a lot of air FLOW

>is essential to avoid toasting the motors.

maybe a powerful blower and a venturi will be better??

Regards

Roland Jollivet

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My friend does plexiglass forming.  Wooden frame, kitchen oven element 

for heater.  Large air-tanks connected to a pump.  These are pumped out, 

then a valve opens and the vacuum forming happens very quickly. 

David

Roland wrote:

{Quote hidden}>>BTW, the hard parts of vacuum forming seem to be the matter of an oven big

>>enough for the work and creating a vacuum source (or is it sink?) with

>>enough volume to draw down the material before the material cools out of the

>>plastic condition...

>>    

>>

>

>Hi 

>

>I've watched vacuum forming done, and it was a very simple set-up. They

>were forming polystyrene(not foam!)

>The positive/pattern was simple wood fabrications, and there was no oven,

>rather a big element and a few fans blowing the air down. I think the

>vacuum part was just an industrial blower, as a sucker.

>

>The force required will depend on the temperature, depth of draw required,

>thickness of sheet, resolution of pattern. Although a nice convoluted

>surface can be obtained, the edges always pose a problem, same with

>fibreglass moulds. Trimming them to an exact size, and polishing to hide

>the work, is almost impossible.

>

>

>  

>

>>A home vacuum cleaner arrangement is not really up to the task. Besides, my

>>earlier experiments with home vacuums lead me to believe a lot of air FLOW

>>is essential to avoid toasting the motors.

>>    

>>

>

>maybe a powerful blower and a venturi will be better??

>

>Regards

>Roland Jollivet

>

>_______________________________________________

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>

>  

>

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David, can you get some pictures from your buddy, perhaps a few more 

details.  What sort of vacuum are we looking at?  100's of PSI's, or what?

-Shawn

David P Harris wrote:

{Quote hidden}> My friend does plexiglass forming.  Wooden frame, kitchen oven element 

> for heater.  Large air-tanks connected to a pump.  These are pumped out, 

> then a valve opens and the vacuum forming happens very quickly. David

> 

> Roland wrote:

> 

>>> BTW, the hard parts of vacuum forming seem to be the matter of an 

>>> oven big

>>> enough for the work and creating a vacuum source (or is it sink?) with

>>> enough volume to draw down the material before the material cools out 

>>> of the

>>> plastic condition...

>>>   

>>

>>

>> Hi

>> I've watched vacuum forming done, and it was a very simple set-up. They

>> were forming polystyrene(not foam!)

>> The positive/pattern was simple wood fabrications, and there was no oven,

>> rather a big element and a few fans blowing the air down. I think the

>> vacuum part was just an industrial blower, as a sucker.

>>

>> The force required will depend on the temperature, depth of draw 

>> required,

>> thickness of sheet, resolution of pattern. Although a nice convoluted

>> surface can be obtained, the edges always pose a problem, same with

>> fibreglass moulds. Trimming them to an exact size, and polishing to hide

>> the work, is almost impossible.

>>

>>

>>  

>>

>>> A home vacuum cleaner arrangement is not really up to the task. 

>>> Besides, my

>>> earlier experiments with home vacuums lead me to believe a lot of air 

>>> FLOW

>>> is essential to avoid toasting the motors.

>>>   

>>

>>

>> maybe a powerful blower and a venturi will be better??

>>

>> Regards

>> Roland Jollivet

>>

>> _______________________________________________

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>>

>>  

>>

> 

> 

> 

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I once built a "Vacuum tank".

It consisted of a refrigeration compressor connected to an old 80 gallon water tank.

Compressor connected to one port, vacuum gauge on another and an air-hose on a third port.

Using an "air-blower" on the hose I had a monster of a desoldering device.

Could also be used to suck-up almost any liquid, which could be drained by opening a valve on the bottom.

Sold it to someone who wanted it more than I and was willing to pay well for it.

I have always intended to build another one-day, but you know how that goes, it's just not as much fun the second time around.

KF4HAZ - Lonnie

----- From: "David P Harris" <dpharris@

{Quote hidden}> My friend does plexiglass forming.  Wooden frame, kitchen oven element 

> for heater.  Large air-tanks connected to a pump.  These are pumped out, 

> then a valve opens and the vacuum forming happens very quickly. 

> David

> 

> Roland wrote:

> 

> >>BTW, the hard parts of vacuum forming seem to be the matter of an oven big

> >>enough for the work and creating a vacuum source (or is it sink?) with

> >>enough volume to draw down the material before the material cools out of the

> >>plastic condition...

> >>    

> >>

> >

> >Hi 

> >

> >I've watched vacuum forming done, and it was a very simple set-up. They

> >were forming polystyrene(not foam!)

> >The positive/pattern was simple wood fabrications, and there was no oven,

> >rather a big element and a few fans blowing the air down. I think the

> >vacuum part was just an industrial blower, as a sucker.

> >

> >The force required will depend on the temperature, depth of draw required,

> >thickness of sheet, resolution of pattern. Although a nice convoluted

> >surface can be obtained, the edges always pose a problem, same with

> >fibreglass moulds. Trimming them to an exact size, and polishing to hide

> >the work, is almost impossible.

> >

> >

> >  

> >

> >>A home vacuum cleaner arrangement is not really up to the task. Besides, my

> >>earlier experiments with home vacuums lead me to believe a lot of air FLOW

> >>is essential to avoid toasting the motors.

> >>    

> >>

> >

> >maybe a powerful blower and a venturi will be better??

> >

> >Regards

> >Roland Jollivet

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14.x PSI is normal atmospheric pressure here on earth, x varies slightly with altitude and baro.

So that is the limit, vacuum is usually expressed in bar or  inches mercury.

1 bar=14.6psi=30inches mercury if memory serves correctly this would be the theoretical absolute vacuum.

In practice if you can get 29 inches vacuum you are doing very good.

KF4HAZ - Lonnie

----- From: "Shawn Wilton" <shawn@

{Quote hidden}> David, can you get some pictures from your buddy, perhaps a few more 

> details.  What sort of vacuum are we looking at?  100's of PSI's, or what?

> 

> -Shawn

> 

> David P Harris wrote:

> > My friend does plexiglass forming.  Wooden frame, kitchen oven element 

> > for heater.  Large air-tanks connected to a pump.  These are pumped out, 

> > then a valve opens and the vacuum forming happens very quickly. David

> > 

> > Roland wrote:

> > 

> >>> BTW, the hard parts of vacuum forming seem to be the matter of an 

> >>> oven big

> >>> enough for the work and creating a vacuum source (or is it sink?) with

> >>> enough volume to draw down the material before the material cools out 

> >>> of the

> >>> plastic condition...

> >>>   

> >>

> >>

> >> Hi

> >> I've watched vacuum forming done, and it was a very simple set-up. They

> >> were forming polystyrene(not foam!)

> >> The positive/pattern was simple wood fabrications, and there was no oven,

> >> rather a big element and a few fans blowing the air down. I think the

> >> vacuum part was just an industrial blower, as a sucker.

> >>

> >> The force required will depend on the temperature, depth of draw 

> >> required,

> >> thickness of sheet, resolution of pattern. Although a nice convoluted

> >> surface can be obtained, the edges always pose a problem, same with

> >> fibreglass moulds. Trimming them to an exact size, and polishing to hide

> >> the work, is almost impossible.

> >>

> >>

> >>  

> >>

> >>> A home vacuum cleaner arrangement is not really up to the task. 

> >>> Besides, my

> >>> earlier experiments with home vacuums lead me to believe a lot of air 

> >>> FLOW

> >>> is essential to avoid toasting the motors.

> >>>   

> >>

> >>

> >> maybe a powerful blower and a venturi will be better??

> >>

> >> Regards

> >> Roland Jollivet

> >>

> >> _______________________________________________

> >> http://www.piclist.com

> >> View/change your membership options at

> >> mailman.mit.edu/mailman/listinfo/piclist

> >>

> >>  

> >>

> > 

> > 

> > 

> > _______________________________________________

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Shawn-

28 mmHg  with a 8x2'  propane tank --- the initial rush is to make sure 

a good seal happens. 

He said for smaller parts with polystyrene, you can use a old barbeque 

propane tank with a new valve on it and attached to a air compressor. 

No pictures, but essentially a flat square board with lots of holes, a 

frame around it, and a chamber below attached to your vacuum.  Set the 

plastic on top and then heat with a heat gun or hair dryer until 

sagging, then let 'er rip. 

David

Shawn Wilton wrote:

{Quote hidden}> David, can you get some pictures from your buddy, perhaps a few more 

> details.  What sort of vacuum are we looking at?  100's of PSI's, or 

> what?

>

> -Shawn

>

> David P Harris wrote:

>

>> My friend does plexiglass forming.  Wooden frame, kitchen oven 

>> element for heater.  Large air-tanks connected to a pump.  These are 

>> pumped out, then a valve opens and the vacuum forming happens very 

>> quickly. David

>>

>> Roland wrote:

>>

>>>> BTW, the hard parts of vacuum forming seem to be the matter of an 

>>>> oven big

>>>> enough for the work and creating a vacuum source (or is it sink?) with

>>>> enough volume to draw down the material before the material cools 

>>>> out of the

>>>> plastic condition...

>>>>   

>>>

>>>

>>>

>>> Hi

>>> I've watched vacuum forming done, and it was a very simple set-up. They

>>> were forming polystyrene(not foam!)

>>> The positive/pattern was simple wood fabrications, and there was no 

>>> oven,

>>> rather a big element and a few fans blowing the air down. I think the

>>> vacuum part was just an industrial blower, as a sucker.

>>>

>>> The force required will depend on the temperature, depth of draw 

>>> required,

>>> thickness of sheet, resolution of pattern. Although a nice convoluted

>>> surface can be obtained, the edges always pose a problem, same with

>>> fibreglass moulds. Trimming them to an exact size, and polishing to 

>>> hide

>>> the work, is almost impossible.

>>>

>>>

>>>  

>>>

>>>> A home vacuum cleaner arrangement is not really up to the task. 

>>>> Besides, my

>>>> earlier experiments with home vacuums lead me to believe a lot of 

>>>> air FLOW

>>>> is essential to avoid toasting the motors.

>>>>   

>>>

>>>

>>>

>>> maybe a powerful blower and a venturi will be better??

>>>

>>> Regards

>>> Roland Jollivet

>>>

>>> _______________________________________________

>>> http://www.piclist.com

>>> View/change your membership options at

>>> mailman.mit.edu/mailman/listinfo/piclist

>>>

>>>  

>>>

>>

>>

>>

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Shawn Wilton wrote:

> David, can you get some pictures from your buddy, perhaps a few more

> details.  What sort of vacuum are we looking at?  100's of PSI's, or

> what?

Huh?  Anything more than about 15 PSI (1 atmosphere) would be a good trick

unless you are making the vacuum inside a pressure chamber.

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Good to know.  Going to have to give this a shot.  Sounds like fun after 

all.  Anyone else building one of these things?  If so, contact me off list.

-Shawn

Falcon Wireless Tech Support - KF4HAZ wrote:

{Quote hidden}> 14.x PSI is normal atmospheric pressure here on earth, x varies slightly with altitude and baro.

> So that is the limit, vacuum is usually expressed in bar or  inches mercury.

> 1 bar=14.6psi=30inches mercury if memory serves correctly this would be the theoretical absolute vacuum.

> In practice if you can get 29 inches vacuum you are doing very good.

> 

> KF4HAZ - Lonnie

> 

> ----- From: "Shawn Wilton" <shawn@

> 

> 

>>David, can you get some pictures from your buddy, perhaps a few more 

>>details.  What sort of vacuum are we looking at?  100's of PSI's, or what?

>>

>>-Shawn

>>

>>David P Harris wrote:

>>

>>>My friend does plexiglass forming.  Wooden frame, kitchen oven element 

>>>for heater.  Large air-tanks connected to a pump.  These are pumped out, 

>>>then a valve opens and the vacuum forming happens very quickly. David

>>>

>>>Roland wrote:

>>>

>>>

>>>>>BTW, the hard parts of vacuum forming seem to be the matter of an 

>>>>>oven big

>>>>>enough for the work and creating a vacuum source (or is it sink?) with

>>>>>enough volume to draw down the material before the material cools out 

>>>>>of the

>>>>>plastic condition...

>>>>>  

>>>>

>>>>

>>>>Hi

>>>>I've watched vacuum forming done, and it was a very simple set-up. They

>>>>were forming polystyrene(not foam!)

>>>>The positive/pattern was simple wood fabrications, and there was no oven,

>>>>rather a big element and a few fans blowing the air down. I think the

>>>>vacuum part was just an industrial blower, as a sucker.

>>>>

>>>>The force required will depend on the temperature, depth of draw 

>>>>required,

>>>>thickness of sheet, resolution of pattern. Although a nice convoluted

>>>>surface can be obtained, the edges always pose a problem, same with

>>>>fibreglass moulds. Trimming them to an exact size, and polishing to hide

>>>>the work, is almost impossible.

>>>>

>>>>

>>>> 

>>>>

>>>>

>>>>>A home vacuum cleaner arrangement is not really up to the task. 

>>>>>Besides, my

>>>>>earlier experiments with home vacuums lead me to believe a lot of air 

>>>>>FLOW

>>>>>is essential to avoid toasting the motors.

>>>>>  

>>>>

>>>>

>>>>maybe a powerful blower and a venturi will be better??

>>>>

>>>>Regards

>>>>Roland Jollivet

>>>>

>>>>_______________________________________________

>>>>http://www.piclist.com

>>>>View/change your membership options at

>>>>mailman.mit.edu/mailman/listinfo/piclist

>>>>

>>>> 

>>>>

>>>

>>>

>>>

>>>_______________________________________________

>>>http://www.piclist.com

>>>View/change your membership options at

>>>mailman.mit.edu/mailman/listinfo/piclist

>>

>>_______________________________________________

>>http://www.piclist.com

>>View/change your membership options at

>>mailman.mit.edu/mailman/listinfo/piclist

>>

> 

> 

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At 01:57 PM 9/15/2004 -0700, you wrote:

>David, can you get some pictures from your buddy, perhaps a few more 

>details.  What sort of vacuum are we looking at?  100's of PSI's, or what?

>

>-Shawn

Vacuum is limited to about 14.7psi. Jovian piclisters can get considerably

higher vacuums, of course.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"

speffspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com

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8x2.  You mean one of those massive propane tanks people in the country 

usually have?

David P Harris wrote:

{Quote hidden}> Shawn-

> 28 mmHg  with a 8x2'  propane tank --- the initial rush is to make sure 

> a good seal happens. He said for smaller parts with polystyrene, you can 

> use a old barbeque propane tank with a new valve on it and attached to a 

> air compressor.

> No pictures, but essentially a flat square board with lots of holes, a 

> frame around it, and a chamber below attached to your vacuum.  Set the 

> plastic on top and then heat with a heat gun or hair dryer until 

> sagging, then let 'er rip.

> David

> 

> 

> 

> Shawn Wilton wrote:

> 

>> David, can you get some pictures from your buddy, perhaps a few more 

>> details.  What sort of vacuum are we looking at?  100's of PSI's, or 

>> what?

>>

>> -Shawn

>>

>> David P Harris wrote:

>>

>>> My friend does plexiglass forming.  Wooden frame, kitchen oven 

>>> element for heater.  Large air-tanks connected to a pump.  These are 

>>> pumped out, then a valve opens and the vacuum forming happens very 

>>> quickly. David

>>>

>>> Roland wrote:

>>>

>>>>> BTW, the hard parts of vacuum forming seem to be the matter of an 

>>>>> oven big

>>>>> enough for the work and creating a vacuum source (or is it sink?) with

>>>>> enough volume to draw down the material before the material cools 

>>>>> out of the

>>>>> plastic condition...

>>>>>   

>>>>

>>>>

>>>>

>>>>

>>>> Hi

>>>> I've watched vacuum forming done, and it was a very simple set-up. They

>>>> were forming polystyrene(not foam!)

>>>> The positive/pattern was simple wood fabrications, and there was no 

>>>> oven,

>>>> rather a big element and a few fans blowing the air down. I think the

>>>> vacuum part was just an industrial blower, as a sucker.

>>>>

>>>> The force required will depend on the temperature, depth of draw 

>>>> required,

>>>> thickness of sheet, resolution of pattern. Although a nice convoluted

>>>> surface can be obtained, the edges always pose a problem, same with

>>>> fibreglass moulds. Trimming them to an exact size, and polishing to 

>>>> hide

>>>> the work, is almost impossible.

>>>>

>>>>

>>>>  

>>>>

>>>>> A home vacuum cleaner arrangement is not really up to the task. 

>>>>> Besides, my

>>>>> earlier experiments with home vacuums lead me to believe a lot of 

>>>>> air FLOW

>>>>> is essential to avoid toasting the motors.

>>>>>   

>>>>

>>>>

>>>>

>>>>

>>>> maybe a powerful blower and a venturi will be better??

>>>>

>>>> Regards

>>>> Roland Jollivet

>>>>

>>>> _______________________________________________

>>>> http://www.piclist.com

>>>> View/change your membership options at

>>>> mailman.mit.edu/mailman/listinfo/piclist

>>>>

>>>>  

>>>>

>>>

>>>

>>>

>>> _______________________________________________

>>> http://www.piclist.com

>>> View/change your membership options at

>>> mailman.mit.edu/mailman/listinfo/piclist

>>

>>

>> _______________________________________________

>> http://www.piclist.com

>> View/change your membership options at

>> mailman.mit.edu/mailman/listinfo/piclist

>>

> 

> 

> 

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Technicalities Olin.  You know what I meant.  Just couldn't remember how 

to specify vacuum.  Surely you have better things to do with your time.  :-P

Olin Lathrop wrote:

{Quote hidden}> Shawn Wilton wrote:

> 

>>David, can you get some pictures from your buddy, perhaps a few more

>>details.  What sort of vacuum are we looking at?  100's of PSI's, or

>>what?

> 

> 

> Huh?  Anything more than about 15 PSI (1 atmosphere) would be a good trick

> unless you are making the vacuum inside a pressure chamber.

> 

> 

> *****************************************************************

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> What sort of vacuum are we looking at?  100's of PSI's, or what?

Max vacuum possible is about 14 psi - ie absence of atmospheric pressure. 

        RM

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I'm recoverying from back surgery, leave me alone!  :-P

At least I have an excuse.  :-D

-Shawn

Russell McMahon wrote:

{Quote hidden}>>What sort of vacuum are we looking at?  100's of PSI's, or what?

> 

> 

> Max vacuum possible is about 14 psi - ie absence of atmospheric pressure. 

> 

> 

> 

>         

>         RM

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Shawn Wilton wrote:

> Technicalities Olin.  You know what I meant.

Not really.  It was only obvious that you were confused.

> Just couldn't remember how

> to specify vacuum.

You got the specifying part right.  It's the how it works part you seemed to

have a problem with.

> Surely you have better things to do with your time.

I suppose.  I didn't want others reading that message to think talking about

100s of PSI of vacuum in that context made sense.  With the list server

delays, I didn't know at the time that many others had jumped in to say the

same thing.

When someone makes a blatant error, people are going to correct it.  That's

the way public forums work.  Get over it.  It wasn't a big deal, but by

objecting to being corrected you are making it one.  I don't think anyone

thought you were stupid for making a simple mistake.  However, you are now

inviting them to think so by complaining about being corrected.

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> I once built a "Vacuum tank".

> It consisted of a refrigeration compressor connected to an old 80 gallon

water tank.

> Compressor connected to one port, vacuum gauge on another and an air-hose

on a third port.

Hmmm.  I once imploded an 80 gallon compressor air tank with the same

maneuver.  Made a lot of noise when it crumbled like a cheap beer can.

Pressure tanks don't make good vacuum tanks.

Win Wiencke

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Standard atmospheric pressure is 14.7 PSI.  Standard barometric pressure is 29.92  inches of Hg.  Both are specified at 0° C at sea level.  24 or 25 inHg is fairly easy to accomplish But I doubt you would need to be that low for vacuum forming.

We got called to repair an old vacuum sealing machine several years ago.  The guy's machine was a flat table with the work area having holes in it as was described by someone else.  The product was laid out on a cardboard sheet with holes punched in it then plastic sheet (polyethylene?) was stretched over a frame above the work area.  Then a heater came on to heat the plastic until it drooped, at which time the frame was lowered and the vacuum pump came on.  It seems the vacuum pump wasn't much more than a squirrel cage blower like those from an old furnace.  Check the cold air return on your furnace.  It has a pretty good air flow, and they're not real expensive...especially if you can find one that was a scrapper.

The heater was an IR type like we now see in some warehouses or other large volume work areas.

REB

Shawn Wilton wrote:

{Quote hidden}> 8x2.  You mean one of those massive propane tanks people in the 

> country usually have?

>

>

> David P Harris wrote:

>

>> Shawn-

>> 28 mmHg  with a 8x2'  propane tank --- the initial rush is to make 

>> sure a good seal happens. He said for smaller parts with polystyrene, 

>> you can use a old barbeque propane tank with a new valve on it and 

>> attached to a air compressor.

>> No pictures, but essentially a flat square board with lots of holes, 

>> a frame around it, and a chamber below attached to your vacuum.  Set 

>> the plastic on top and then heat with a heat gun or hair dryer until 

>> sagging, then let 'er rip.

>> David

>>

>>

>

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You pulled all the fun out of that post.  I mean all of it.  Thank you 

for the correction.  I would give you a big hug, but I don't give hugs.

:-P

Olin Lathrop wrote:

{Quote hidden}> Shawn Wilton wrote:

> 

>>Technicalities Olin.  You know what I meant.

> 

> 

> Not really.  It was only obvious that you were confused.

> 

> 

>>Just couldn't remember how

>>to specify vacuum.

> 

> 

> You got the specifying part right.  It's the how it works part you seemed to

> have a problem with.

> 

> 

>>Surely you have better things to do with your time.

> 

> 

> I suppose.  I didn't want others reading that message to think talking about

> 100s of PSI of vacuum in that context made sense.  With the list server

> delays, I didn't know at the time that many others had jumped in to say the

> same thing.

> 

> When someone makes a blatant error, people are going to correct it.  That's

> the way public forums work.  Get over it.  It wasn't a big deal, but by

> objecting to being corrected you are making it one.  I don't think anyone

> thought you were stupid for making a simple mistake.  However, you are now

> inviting them to think so by complaining about being corrected.

> 

> 

> *****************************************************************

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On Tue, 14 Sep 2004, John Ferrell wrote:

> A home vacuum cleaner arrangement is not really up to the task. Besides, my

> earlier experiments with home vacuums lead me to believe a lot of air FLOW

> is essential to avoid toasting the motors.

That is true, but you do not need absolute vacuum for pulling the plastic 

so an adjustable leak in the vacuum line will let in enough air for the 

motor to cool itself. Also it pays to look at rpm limiting the motor. I 

have destroyed 1 motor by over-revving it in vacuum (not by overheating). 

I estimate that the rpm at least doubled when the vacuum side was properly 

sealed. Nomimnal was about 35,000 rpm at 0.3at vacuum. If the rpm had 

doubled it would have overloaded the outer parts of the armature to 4 

times nominal mechanical load. In my case the armature became unbalanced 

and touched the stator, and then welded itself to the stator when some 

plastic parts melted. The impulse caused the motor, which was not bolted 

down, to start rolling on the floor. I have also heard of overdriven 

vacuum cleaner motors causing the aluminium turbines to explode and shred 

holes in the turbine housing.

I believe that using pressure instead of vacuum is easier even if more 

labor is required (hold down dogs or screws for the frame). It may also be 

more dangerous, pressure could cause explosive atmosphere with solvents 

from the plastic or cause structural failure in the mold and a small 

explosion.

Peter

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> Vacuum is limited to about 14.7psi. Jovian piclisters can get considerably

> higher vacuums, of course.

Many are Jovial, but few are Jovian. 

-- Lawrence Lile, P.E.

Electrical and Electronic Solutions

Project Solutions Companies

http://www.projsolco.com

> {Original Message removed}
Lawrence Lile wrote:

> Many [PIClisters] are Jovial, but few are Jovian.

Maybe the server is, which could explain the long time delays.

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Lawrence,

On Thu, 16 Sep 2004 07:20:36 -0500, Lawrence Lile wrote:

> > Vacuum is limited to about 14.7psi. Jovian piclisters can get considerably

> > higher vacuums, of course.

> 

> Many are Jovial, but few are Jovian. 

Not enough of them are Jovial, IMHO!  :-)

This whole thing just goes to show that "vacuum forming" is really a misnomer.  It ought to be called 

"Atmospheric forming"...

Cheers,

Howard Winter

St.Albans, England

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>

>This whole thing just goes to show that "vacuum forming" is really a misnomer.  It ought to be called 

>"Atmospheric forming"...

Forget that, explosive forming looks like a lot more fun! 

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>This whole thing just goes to show that "vacuum forming" 

>is really a misnomer.  It ought to be called 

>"Atmospheric forming"...

Oh, you mean like the Atmospheric Railway :))

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Yes, but he does this commercially in his Plexiglass shop while forming 

full thickness plexiglass.  For people like us, much smaller tanks can 

be used. 

David

Shawn Wilton wrote:

{Quote hidden}> 8x2.  You mean one of those massive propane tanks people in the 

> country usually have?

>

>

> David P Harris wrote:

>

>> Shawn-

>> 28 mmHg  with a 8x2'  propane tank --- the initial rush is to make 

>> sure a good seal happens. He said for smaller parts with polystyrene, 

>> you can use a old barbeque propane tank with a new valve on it and 

>> attached to a air compressor.

>> No pictures, but essentially a flat square board with lots of holes, 

>> a frame around it, and a chamber below attached to your vacuum.  Set 

>> the plastic on top and then heat with a heat gun or hair dryer until 

>> sagging, then let 'er rip.

>> David

>>

>>

>>

>> Shawn Wilton wrote:

>>

>>> David, can you get some pictures from your buddy, perhaps a few more 

>>> details.  What sort of vacuum are we looking at?  100's of PSI's, or 

>>> what?

>>>

>>> -Shawn

>>>

>>> David P Harris wrote:

>>>

>>>> My friend does plexiglass forming.  Wooden frame, kitchen oven 

>>>> element for heater.  Large air-tanks connected to a pump.  These 

>>>> are pumped out, then a valve opens and the vacuum forming happens 

>>>> very quickly. David

>>>>

>>>> Roland wrote:

>>>>

>>>>>> BTW, the hard parts of vacuum forming seem to be the matter of an 

>>>>>> oven big

>>>>>> enough for the work and creating a vacuum source (or is it sink?) 

>>>>>> with

>>>>>> enough volume to draw down the material before the material cools 

>>>>>> out of the

>>>>>> plastic condition...

>>>>>>   

>>>>>

>>>>>

>>>>>

>>>>>

>>>>>

>>>>> Hi

>>>>> I've watched vacuum forming done, and it was a very simple set-up. 

>>>>> They

>>>>> were forming polystyrene(not foam!)

>>>>> The positive/pattern was simple wood fabrications, and there was 

>>>>> no oven,

>>>>> rather a big element and a few fans blowing the air down. I think the

>>>>> vacuum part was just an industrial blower, as a sucker.

>>>>>

>>>>> The force required will depend on the temperature, depth of draw 

>>>>> required,

>>>>> thickness of sheet, resolution of pattern. Although a nice convoluted

>>>>> surface can be obtained, the edges always pose a problem, same with

>>>>> fibreglass moulds. Trimming them to an exact size, and polishing 

>>>>> to hide

>>>>> the work, is almost impossible.

>>>>>

>>>>>

>>>>>  

>>>>>

>>>>>> A home vacuum cleaner arrangement is not really up to the task. 

>>>>>> Besides, my

>>>>>> earlier experiments with home vacuums lead me to believe a lot of 

>>>>>> air FLOW

>>>>>> is essential to avoid toasting the motors.

>>>>>>   

>>>>>

>>>>>

>>>>>

>>>>>

>>>>>

>>>>> maybe a powerful blower and a venturi will be better??

>>>>>

>>>>> Regards

>>>>> Roland Jollivet

>>>>>

>>>>> _______________________________________________

>>>>> http://www.piclist.com

>>>>> View/change your membership options at

>>>>> mailman.mit.edu/mailman/listinfo/piclist

>>>>>

>>>>>  

>>>>>

>>>>

>>>>

>>>>

>>>> _______________________________________________

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>>>> mailman.mit.edu/mailman/listinfo/piclist

>>>

>>>

>>>

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>>>

>>

>>

>>

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Ok, that was the sort of clarification I required.  Thanks Dave.

David P Harris wrote:

{Quote hidden}> Yes, but he does this commercially in his Plexiglass shop while forming 

> full thickness plexiglass.  For people like us, much smaller tanks can 

> be used. David

> 

> Shawn Wilton wrote:

> 

>> 8x2.  You mean one of those massive propane tanks people in the 

>> country usually have?

>>

>>

>> David P Harris wrote:

>>

>>> Shawn-

>>> 28 mmHg  with a 8x2'  propane tank --- the initial rush is to make 

>>> sure a good seal happens. He said for smaller parts with polystyrene, 

>>> you can use a old barbeque propane tank with a new valve on it and 

>>> attached to a air compressor.

>>> No pictures, but essentially a flat square board with lots of holes, 

>>> a frame around it, and a chamber below attached to your vacuum.  Set 

>>> the plastic on top and then heat with a heat gun or hair dryer until 

>>> sagging, then let 'er rip.

>>> David

>>>

>>>

>>>

>>> Shawn Wilton wrote:

>>>

>>>> David, can you get some pictures from your buddy, perhaps a few more 

>>>> details.  What sort of vacuum are we looking at?  100's of PSI's, or 

>>>> what?

>>>>

>>>> -Shawn

>>>>

>>>> David P Harris wrote:

>>>>

>>>>> My friend does plexiglass forming.  Wooden frame, kitchen oven 

>>>>> element for heater.  Large air-tanks connected to a pump.  These 

>>>>> are pumped out, then a valve opens and the vacuum forming happens 

>>>>> very quickly. David

>>>>>

>>>>> Roland wrote:

>>>>>

>>>>>>> BTW, the hard parts of vacuum forming seem to be the matter of an 

>>>>>>> oven big

>>>>>>> enough for the work and creating a vacuum source (or is it sink?) 

>>>>>>> with

>>>>>>> enough volume to draw down the material before the material cools 

>>>>>>> out of the

>>>>>>> plastic condition...

>>>>>>>   

>>>>>>

>>>>>>

>>>>>>

>>>>>>

>>>>>>

>>>>>>

>>>>>> Hi

>>>>>> I've watched vacuum forming done, and it was a very simple set-up. 

>>>>>> They

>>>>>> were forming polystyrene(not foam!)

>>>>>> The positive/pattern was simple wood fabrications, and there was 

>>>>>> no oven,

>>>>>> rather a big element and a few fans blowing the air down. I think the

>>>>>> vacuum part was just an industrial blower, as a sucker.

>>>>>>

>>>>>> The force required will depend on the temperature, depth of draw 

>>>>>> required,

>>>>>> thickness of sheet, resolution of pattern. Although a nice convoluted

>>>>>> surface can be obtained, the edges always pose a problem, same with

>>>>>> fibreglass moulds. Trimming them to an exact size, and polishing 

>>>>>> to hide

>>>>>> the work, is almost impossible.

>>>>>>

>>>>>>

>>>>>>  

>>>>>>

>>>>>>> A home vacuum cleaner arrangement is not really up to the task. 

>>>>>>> Besides, my

>>>>>>> earlier experiments with home vacuums lead me to believe a lot of 

>>>>>>> air FLOW

>>>>>>> is essential to avoid toasting the motors.

>>>>>>>   

>>>>>>

>>>>>>

>>>>>>

>>>>>>

>>>>>>

>>>>>>

>>>>>> maybe a powerful blower and a venturi will be better??

>>>>>>

>>>>>> Regards

>>>>>> Roland Jollivet

>>>>>>

>>>>>> _______________________________________________

>>>>>> http://www.piclist.com

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>>>>>>

>>>>>>  

>>>>>>

>>>>>

>>>>>

>>>>>

>>>>> _______________________________________________

>>>>> http://www.piclist.com

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>>>>

>>>>

>>>>

>>>>

>>>> _______________________________________________

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>>>>

>>>

>>>

>>>

>>> _______________________________________________

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>>

>>

>> _______________________________________________

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> 

> 

> 

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Actually, it's more like 0 psi  or 0 bar or whatever unit you prefer.

You could get a better effect for forming your workpiece by using compressed 

air pushing instead of sucking on the other side.

That would be blowmolding instead of vacuumforming

>> Vacuum is limited to about 14.7psi. Jovian piclisters can get 

>> considerably

>> higher vacuums, of course.

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At 05:22 PM 9/16/2004 -0400, you wrote:

>Actually, it's more like 0 psi  or 0 bar or whatever unit you prefer.

>You could get a better effect for forming your workpiece by using 

>compressed air pushing instead of sucking on the other side.

This level of vacuum (not very high) is usually specified in units of

gauge pressure- referenced to atmospheric- not absolute pressure. That's

why several of us gave the same answer of ~15psi, and that's also what's

meant when vacuum is given as "inches of water". 0" is no vacuum (atmospheric),

not a perfect vacuum. Same with inches of mercury.

When you start talking about relatively high vacuums, it gets reversed and

we start using units referring to absolute pressure such as torr or

microns (of an atmosphere). But that's not the level of vacuum used in this

kind of device.

>That would be blowmolding instead of vacuumforming

Blowmolding is cool. Nothing really sounds like that. Back when it was

high-tech I did work on parison controllers.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"

@spam@speffKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com

Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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Alan,

On Thu, 16 Sep 2004 15:28:58 +0100, Alan B. Pearce 

wrote:

> >This whole thing just goes to show that "vacuum 

forming" 

> >is really a misnomer.  It ought to be called 

> >"Atmospheric forming"...

> 

> Oh, you mean like the Atmospheric Railway :))

Indeed!  Good old Brunel - shame about the rats!  :-)

Cheers,

Howard Winter

St.Albans, England

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I will agree that many of the current day air-compressor tanks

 are not heavy enough to withstand 14.6 psi external with 0 internal.

But this was one of the old (1940's) 1/4" thick steel water tanks,

 basically a cylinder with a hemispherical dome on top,

 and a reversed one on the bottom.

The ideal shape for a vacuum tank would be a sphere.

Where I once worked we got a 10hp 3 phase 250 gallon industrial air compressor.

When  we first connected it the motor ran backwards,

 but we caught it quickly and swapped 2 of the 3-phase legs and everything was ok.

3-Phase motors are a 50-50 shot when first wired,

 swapping any 2 of the legs reverses the rotation.

One last word of caution, not all compressors work as vacuum pumps when reversed.

 It depends on their design, some have a cam and valves, others have checkvalves,

and there are other variations & combinations,

some of which will work as compressors regardless of rotation,

 and some will self destruct due to the cam operated valves fighting the other stages checkvalves.

KF4HAZ - Lonnie

----- From: "Win Wiencke" <Win@

{Quote hidden}> > I once built a "Vacuum tank".

> > It consisted of a refrigeration compressor connected to an old 80 gallon

> water tank.

> > Compressor connected to one port, vacuum gauge on another and an air-hose

> on a third port.

> 

> Hmmm.  I once imploded an 80 gallon compressor air tank with the same

> maneuver.  Made a lot of noise when it crumbled like a cheap beer can.

> Pressure tanks don't make good vacuum tanks.

> 

> Win Wiencke

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