Does a vacuum press improve a glue joint between a veneer and a flat, smooth
substrate (say.... MDF)? If so, why? What fundamental physical properties
of the veneer, substrate, or glue are changed by the vacuum that improve the
surface joint?
Or is a vacuum press just effective for gluing veneer to curved or irregular
surfaces?
Thanks a heap,
-jbb
"J. Clarke" <[email protected]> wrote in message news:<[email protected]>...
> You're neglecting the effect of dissolved gases and outgassing.
Why not neglect them ? This is only woodworking after all. Our
vacuums are pretty rough - they're just in the "mechanical" region,
not the "chemistry" or "physics" regions.
Woodworking has two uses for vacuum; clamping and de-bubbling. For
clamping, then you could equally well put it all in a hyperbaric
chamber and apply a little excess pressure to the outside. So long as
you have a few psi difference, then that's all you need.
For de-bubbling (such as casting thick epoxy or polyurethane resins)
you only need to drop the pressure below the pressure at which the
resin was mixed, which is presumably atmospheric (some commercial
systems mix under pressure to avoid the need for vacuum afterwards).
For most of my "potting" work I use a Vac-U-Vin wine storer and a hand
pump to get down to about 1/4 atmosphere - this de-bubbles 2"
cylinders fine. You _don't_ need to "lower the pressure to the vapour
pressure of the resin", as is sometimes claimed.
And yes, I _have_ built steel hard-vacuum systems with heaters in the
walls to outgass them. I used to be a laser fizzicist.
In rec.woodworking
"J.B. Bobbitt" <[email protected]> wrote:
>Does a vacuum press improve a glue joint between a veneer and a flat, smooth
>substrate (say.... MDF)? If so, why? What fundamental physical properties
>of the veneer, substrate, or glue are changed by the vacuum that improve the
>surface joint?
>
>Or is a vacuum press just effective for gluing veneer to curved or irregular
>surfaces?
Equal distribution of pressure over the entire surface area. Pressure with
clamps, even using flat cauls still leaves room for hot spots to form under
the clamps and uneven distribution due to surface variations, etc.
When the bag is empty, there is an even 14.8 psi (1 atmosphere) uniformly
distributed over the entire surface. Imagine diving to the bottom of a
pool. Every part of your body is under the same pressure as long as you
are at the same depth. Eardrums too ;)
On Wed, 30 Jun 2004 01:26:07 GMT, "J.B. Bobbitt"
<[email protected]> wrote:
>Does a vacuum press improve a glue joint between a veneer and a flat, smooth
>substrate (say.... MDF)? If so, why? What fundamental physical properties
>of the veneer, substrate, or glue are changed by the vacuum that improve the
>surface joint?
>
>Or is a vacuum press just effective for gluing veneer to curved or irregular
>surfaces?
>
>Thanks a heap,
>-jbb
>
you don't say what you want to compare it to.
vacuum presses apply VERY even pressure over the whole surface....
On Wed, 30 Jun 2004 17:08:49 GMT, "Mike Hide" <[email protected]>
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
OK. I can see that up to a point..
...no I can't. The glue is also under the vacuum, and therefore will
no more be forced into the wood than by sheer pressure on the
substrate/veneer. Pressure on its own would force the glue into the
somewhat porous material. The vacuum will "draw" in both directions,
unless you carefully sealed the edges of the board under work.
I can see that it may make _some_ difference, with a shorter, wider
path through the wood than out the edges. But I would wonder at how
difference it makes.
>Ah there you have it, it is not pressure is it , When you apply glue
>everything is at atmospheric pressure . When the veneer is placed on the
>substrate it also is at atmospheric pressure . As the vacuum is applied the
>veneer and the substrate both being to some degree porus air is pulled from
>these and the remaing voids will be sucked into the voids until the pressure
>[ vacuum] at the glue line is the same as the common pressure in the bag
>Anyway thats what I think.....mjh
Ah there you have it, it is not pressure is it , When you apply glue
everything is at atmospheric pressure . When the veneer is placed on the
substrate it also is at atmospheric pressure . As the vacuum is applied the
veneer and the substrate both being to some degree porus air is pulled from
these and the remaing voids will be sucked into the voids until the pressure
[ vacuum] at the glue line is the same as the common pressure in the bag
Anyway thats what I think.....mjh
--
http://members.tripod.com/mikehide2
"Old Nick" <[email protected]> wrote in message
news:[email protected]...
> On Wed, 30 Jun 2004 13:44:04 GMT, Rick Stein <[email protected]>
> vaguely proposed a theory
> ......and in reply I say!:
>
> remove ns from my header address to reply via email
>
>
> HeyMan! You is a universal fish cooker! Wotchuno?
>
> <G>
>
> >One other subtle feature is that the glue is absorbed deeper into the
> >substrate and the veneer.
>
> Seriously. How? I can see the more even theory. But pressure is
> pressure.
Bruce wrote:
> In rec.woodworking
> "J.B. Bobbitt" <[email protected]> wrote:
>
>
>>Does a vacuum press improve a glue joint between a veneer and a flat, smooth
>>substrate (say.... MDF)? If so, why? What fundamental physical properties
>>of the veneer, substrate, or glue are changed by the vacuum that improve the
>>surface joint?
>>
>>Or is a vacuum press just effective for gluing veneer to curved or irregular
>>surfaces?
>
>
> Equal distribution of pressure over the entire surface area. Pressure with
> clamps, even using flat cauls still leaves room for hot spots to form under
> the clamps and uneven distribution due to surface variations, etc.
>
> When the bag is empty, there is an even 14.8 psi (1 atmosphere) uniformly
> distributed over the entire surface. Imagine diving to the bottom of a
> pool. Every part of your body is under the same pressure as long as you
> are at the same depth. Eardrums too ;)
One other subtle feature is that the glue is absorbed deeper into the
substrate and the veneer.
R.
In article <[email protected]>,
J.B. Bobbitt <[email protected]> wrote:
>Does a vacuum press improve a glue joint between a veneer and a flat, smooth
>substrate (say.... MDF)? If so, why? What fundamental physical properties
>of the veneer, substrate, or glue are changed by the vacuum that improve the
>surface joint?
>
The vacuum isn't doing anything magical - it's just a convenient way to
get very even pressure over a large surface. Large, even pressure
gives a thin glue line with intimate contact between the veneer and
the substrate. You can do the same with cauls and a boatload of clamps
but a vacuum press is a whole lot faster and easier. A vacuum press
is also cheaper than the gazillion clamps you'd need for anything larger
than a breadbox.
--
Scott Post [email protected] http://home.insightbb.com/~sepost/
Old Nick wrote:
> On Wed, 30 Jun 2004 17:08:49 GMT, "Mike Hide" <[email protected]>
> vaguely proposed a theory
> ......and in reply I say!:
>
> remove ns from my header address to reply via email
>
> OK. I can see that up to a point..
>
> ...no I can't. The glue is also under the vacuum, and therefore will
> no more be forced into the wood than by sheer pressure on the
> substrate/veneer. Pressure on its own would force the glue into the
> somewhat porous material. The vacuum will "draw" in both directions,
> unless you carefully sealed the edges of the board under work.
>
> I can see that it may make _some_ difference, with a shorter, wider
> path through the wood than out the edges. But I would wonder at how
> difference it makes.
You're neglecting the effect of dissolved gases and outgassing.
>>Ah there you have it, it is not pressure is it , When you apply glue
>>everything is at atmospheric pressure . When the veneer is placed on the
>>substrate it also is at atmospheric pressure . As the vacuum is applied
>>the veneer and the substrate both being to some degree porus air is pulled
>>from these and the remaing voids will be sucked into the voids until the
>>pressure
>>[ vacuum] at the glue line is the same as the common pressure in the bag
>>Anyway thats what I think.....mjh
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)
Old Nick wrote:
> On Thu, 01 Jul 2004 16:17:18 -0400, "J. Clarke"
> <[email protected]> vaguely proposed a theory
> ......and in reply I say!:
>
> remove ns from my header address to reply via email
>
>
>>You're neglecting the effect of dissolved gases and outgassing.
>
> And they would be...? Serious. What sort of effect is this, and how
> difference does it make?
Pull a vacuum on _anything_ and gases come out of it. What quantity depends
on the composition and porosity of the substance. Depending on how the
vacuum bag is arranged, the gases coming out of the wood or the expansion
of gas bubbles and evaporation of volatiles (water is a volatile in this
context, the organic solvents even more so for the most part) entrained in
the glue should drive the glue into the grain to some extent. What extent
is going to depend on the particular composition of the glue and the type
of wood being used, so there's no way to generalize.
> Thanks
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)
In article <[email protected]>,
Old Nick <[email protected]> wrote:
>On Wed, 30 Jun 2004 17:08:49 GMT, "Mike Hide" <[email protected]>
>vaguely proposed a theory
>......and in reply I say!:
> ...
>OK. I can see that up to a point..
>
>...no I can't. The glue is also under the vacuum, and therefore will
>no more be forced into the wood than by sheer pressure on the
>substrate/veneer. Pressure on its own would force the glue into the
>somewhat porous material. The vacuum will "draw" in both directions,
>unless you carefully sealed the edges of the board under work.
>
>I can see that it may make _some_ difference, with a shorter, wider
>path through the wood than out the edges. But I would wonder at how
>difference it makes.
There is a difference between a vacuum and a vacuum press.
You analysis seems to be suitable for a wood/glue/wood sandwich placed
in a vacuum chamber.
But a vacuum press is really doing something different - and it
doesn't need to have a "good" vacuum. The vacuum is used to apply
*pressure* to the wood at some fraction of the 15psi atmospheric
pressure. If the "bladder" can be pumped down to 1/3 atmosphere, all of
the wood which is touched by the bladder will have 10psi pressing it
together. It will have a lower air pressure there, so it will outgas
to some extent - but the main phenomenon is that large force assisting
gluing.
--
--henry schaffer
hes _AT_ ncsu _DOT_ edu
On Thu, 01 Jul 2004 16:17:18 -0400, "J. Clarke"
<[email protected]> vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
>You're neglecting the effect of dissolved gases and outgassing.
And they would be...? Serious. What sort of effect is this, and how
difference does it make?
Thanks
On Wed, 30 Jun 2004 13:44:04 GMT, Rick Stein <[email protected]>
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
HeyMan! You is a universal fish cooker! Wotchuno?
<G>
>One other subtle feature is that the glue is absorbed deeper into the
>substrate and the veneer.
Seriously. How? I can see the more even theory. But pressure is
pressure.
On 2 Jul 2004 03:59:53 -0700, [email protected] (Andy Dingley)
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
Sorry if this was already a play on words by you, but a laser
fizzicist that deals with outgassing just had to be commented
on....<G>
feel free to take full credit....
>And yes, I _have_ built steel hard-vacuum systems with heaters in the
>walls to outgass them. I used to be a laser fizzicist.
On Fri, 9 Jul 2004 01:07:40 +0000 (UTC), [email protected] (Henry E
Schaffer) vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
Actually, confused as I am I basically agree with you. that is what I
thought. IT's mainly pressure, not vacuum, at work here. That was what
I was trying to say several posts back. But I was willing to listen to
ideas, and perhaps became a little lost
> There is a difference between a vacuum and a vacuum press.
>
> You analysis seems to be suitable for a wood/glue/wood sandwich placed
>in a vacuum chamber.
>
> But a vacuum press is really doing something different - and it
>doesn't need to have a "good" vacuum. The vacuum is used to apply
>*pressure* to the wood at some fraction of the 15psi atmospheric
>pressure. If the "bladder" can be pumped down to 1/3 atmosphere, all of
>the wood which is touched by the bladder will have 10psi pressing it
>together. It will have a lower air pressure there, so it will outgas
>to some extent - but the main phenomenon is that large force assisting
>gluing.
On Wed, 30 Jun 2004 01:52:56 GMT, [email protected] (Bruce) vaguely
proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
...and schchchwwp....you are stuck firmly to the bottom of the
pool....<G>
>Imagine diving to the bottom of a
>pool. Every part of your body is under the same pressure as long as you
>are at the same depth. Eardrums too ;)