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'[EE:] Home vacuum-forming'
2004\09\13@193325 by Jinx

face picon face
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

===============================================
If you aren't part of the solution, you're part of the precipitate



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2004\09\13@220952 by Josh Koffman

face picon face
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.
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On Tue, 14 Sep 2004 11:32:05 +1200, Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.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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2004\09\13@224255 by Spehro Pefhany

picon face
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"
.....speffKILLspamspam@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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2004\09\13@225839 by William Chops Westfield

face picon face

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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2004\09\13@231545 by Jinx

face picon face
> 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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2004\09\14@043651 by Alan B. Pearce

face picon face
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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2004\09\14@044253 by Alan B. Pearce

face picon face
>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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2004\09\14@053851 by Jinx

face picon face
> 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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2004\09\14@054127 by Jinx

face picon face
> 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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2004\09\14@075404 by Russell McMahon

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flavicon
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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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2004\09\14@150440 by Peter L. Peres

picon face


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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2004\09\14@150442 by Peter L. Peres

picon face

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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2004\09\14@160816 by SHands

flavicon
face
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}

2004\09\14@162721 by John Ferrell

face picon face
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}

2004\09\14@192133 by Dave King

flavicon
face
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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2004\09\14@195124 by Jinx

face picon face
> 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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2004\09\15@041236 by Alan B. Pearce

face picon face
>> 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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2004\09\15@063052 by Russell McMahon

face
flavicon
face
> 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

______________________________________________

From: Peter L. Peres <plpspamKILLspamACTCOM.CO.IL>
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.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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2004\09\15@133244 by Roland

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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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2004\09\15@164355 by David P Harris

picon face
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}

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2004\09\15@165754 by Shawn Wilton

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face
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}

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2004\09\15@172659 by Support - KF4HAZ

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face
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}

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2004\09\15@173601 by Support - KF4HAZ

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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}

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2004\09\15@175219 by David P Harris

picon face
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}

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2004\09\15@175356 by olin_piclist

face picon face
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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(978) 742-9014, http://www.embedinc.com
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2004\09\15@175510 by Shawn Wilton

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face
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}

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2004\09\15@180329 by Spehro Pefhany

picon face
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"
speffspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




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2004\09\15@181601 by Shawn Wilton

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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}

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2004\09\15@181701 by Shawn Wilton

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face
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}

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2004\09\15@185204 by Russell McMahon

face
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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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2004\09\15@190617 by Shawn Wilton

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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}

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2004\09\15@191606 by olin_piclist

face picon face
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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2004\09\15@200155 by Win Wiencke

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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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2004\09\15@211452 by R. Burrage

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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:

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2004\09\15@221646 by Shawn Wilton

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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:

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2004\09\16@080323 by Peter L. Peres

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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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2004\09\16@082513 by Lawrence Lile

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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}

2004\09\16@085331 by olin_piclist

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Lawrence Lile wrote:
> Many [PIClisters] are Jovial, but few are Jovian.

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

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
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2004\09\16@092215 by Howard Winter

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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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2004\09\16@101220 by Dave VanHorn

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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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2004\09\16@102712 by Alan B. Pearce

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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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2004\09\16@110512 by David P Harris

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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

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2004\09\16@130656 by Shawn Wilton

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


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2004\09\16@172245 by Peter van Hoof

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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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2004\09\16@201730 by Spehro Pefhany

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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@speffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




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2004\09\17@090233 by Howard Winter

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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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2004\09\17@111936 by Support - KF4HAZ

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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@
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