Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed
spreader then went over it with a sponge roller (apparently it's
important not to have too much glue as it can push through the veneer).
With the veneer positioned I placed it on a piece of MDF and then
stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure to force a thin glue line:
so either
(i) more pressure; and/or
(ii) mix the glue a bit runnier.

Am I on the right track? If so how much pressure am I going to need?
Curved cauls + cramps? Vacuum bag??
Is there something fundamental I've missed??

And am I right in thinking that this piece isn't usable as the
veneers could delaminate in the future?



g.

graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit
like a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a
toothed spreader then went over it with a sponge roller (apparently
it's important not to have too much glue as it can push through the
veneer). With the veneer positioned I placed it on a piece of MDF and
then stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure to force a thin glue
line: so either
(i) more pressure; and/or
(ii) mix the glue a bit runnier.

Am I on the right track? If so how much pressure am I going to need?
Curved cauls + cramps? Vacuum bag??
Is there something fundamental I've missed??

And am I right in thinking that this piece isn't usable as the
veneers could delaminate in the future?


How long was it under weight and how much flaked off when trimming? Flaked
off cross or with grain?



--

dadiOH
____________________________

Winters getting colder? Tired of the rat race?
Maybe just ready for a change? Check it out...
http://www.floridaloghouse.net

On 11/18/2012 7:23 AM, graham wrote:
....

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed
spreader then went over it with a sponge roller (apparently it's
important not to have too much glue as it can push through the veneer).
With the veneer positioned I placed it on a piece of MDF and then
stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure...

Indeed. You need either a press or at a minimum cauls/clamping. You
need something at a minimum of 50psi which translates to a lot of total
force over a larger surface.

A useful general paper on using--
http://www.djmarks.com/pdf/ureaglue.pdf

--

dadiOH wrote on 18/11/12 15:54:
graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit
like a nasty bit of far eastern ply.

snip


How long was it under weight

12 hours


and how much flaked off when trimming?

a couple of corners; one a triangle with sides 2cm x 2cm along the panel
edges (this the burr veneer)


Flaked off cross or with grain?
Can't really tell on the burr; on the face veneer the flaking is
predominantly with the veneer grain, having lifted from the edge grain
end. But that's just because my cutting wasn't as gentle as it could
have been - I can lift the edges protruding over the sides (ie. the
veneer long grain) and there's a degree of lifting too (if I continued
the veneer would snap before much came off)

g.

On 11/18/2012 8:23 AM, graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed
spreader then went over it with a sponge roller (apparently it's
important not to have too much glue as it can push through the veneer).
With the veneer positioned I placed it on a piece of MDF and then
stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure to force a thin glue line:
so either
(i) more pressure; and/or
(ii) mix the glue a bit runnier.

Am I on the right track? If so how much pressure am I going to need?
Curved cauls + cramps? Vacuum bag??
Is there something fundamental I've missed??

And am I right in thinking that this piece isn't usable as the
veneers could delaminate in the future?



g.
Did you rough up the mdf surface a little?
I had glued some mdf w/epoxy and it didn't stick.
That indicated to me that either too smooth, or a release agent inteferred.

I sanded w/220 the next time same batch of mdf and tried again. No
problem.

I still don't know why... but a mechanical bond and removing whatever
might have been on the surface cured the problem the next time.

It was an expensive lesson, as the veneer was ruined (ETIMOE curly) like
this http://tinyurl.com/bqdxaop

On 11/18/2012 12:16 PM, tiredofspam wrote:
On 11/18/2012 8:23 AM, graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed
spreader then went over it with a sponge roller (apparently it's
important not to have too much glue as it can push through the veneer).
With the veneer positioned I placed it on a piece of MDF and then
stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure to force a thin glue line:
so either
(i) more pressure; and/or
(ii) mix the glue a bit runnier.

Am I on the right track? If so how much pressure am I going to need?
Curved cauls + cramps? Vacuum bag??
Is there something fundamental I've missed??

And am I right in thinking that this piece isn't usable as the
veneers could delaminate in the future?



g.
Did you rough up the mdf surface a little?
I had glued some mdf w/epoxy and it didn't stick.
That indicated to me that either too smooth, or a release agent inteferred.

I sanded w/220 the next time same batch of mdf and tried again. No problem.

I still don't know why... but a mechanical bond and removing whatever
might have been on the surface cured the problem the next time.

It was an expensive lesson, as the veneer was ruined (ETIMOE curly) like
this http://tinyurl.com/bqdxaop

I should mention that my situation happened with a vacuum bagged setup.

tiredofspam wrote on 18/11/12 17:16:
On 11/18/2012 8:23 AM, graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

snip

Did you rough up the mdf surface a little?
I had glued some mdf w/epoxy and it didn't stick.
That indicated to me that either too smooth, or a release agent inteferred.

I sanded w/220 the next time same batch of mdf and tried again. No problem.

I still don't know why... but a mechanical bond and removing whatever
might have been on the surface cured the problem the next time.

It was an expensive lesson, as the veneer was ruined (ETIMOE curly) like
this http://tinyurl.com/bqdxaop


Thanks for the idea - yes, I did sand the substrate (ply, not mdf).
I can relate to the expensive lesson. At least I have a couple of spare
sheets. I knew I should have done some practice runs but I was too
enthusiastic..

g.

On Sun, 18 Nov 2012 17:27:02 +0000, graham wrote:

Thanks for the idea - yes, I did sand the substrate (ply, not mdf). I
can relate to the expensive lesson. At least I have a couple of spare
sheets. I knew I should have done some practice runs but I was too
enthusiastic..

Being a Neandertal, I have to suggest using hot hide glue and a veneer
hammer next time. No clamps required. If it gels too fast add a little
urea.

But practice on scrap first. It does take a little getting used to.

--
When fascism comes to America, it will be wrapped in the flag and
carrying a cross.

"graham" wrote in message ...

Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed
spreader then went over it with a sponge roller (apparently it's
important not to have too much glue as it can push through the veneer).
With the veneer positioned I placed it on a piece of MDF and then
stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure to force a thin glue line:
so either
(i) more pressure; and/or
(ii) mix the glue a bit runnier.

Am I on the right track? If so how much pressure am I going to need?
Curved cauls + cramps? Vacuum bag??
Is there something fundamental I've missed??

And am I right in thinking that this piece isn't usable as the
veneers could delaminate in the future?



The only time I used Veneer was about 25 years ago. Covered all the interior
doors and door trim with mahogany. Used contact cement. All is still intact.
WW

Larry Blanchard wrote in :

On Sun, 18 Nov 2012 17:27:02 +0000, graham wrote:

Thanks for the idea - yes, I did sand the substrate (ply, not mdf). I
can relate to the expensive lesson. At least I have a couple of spare
sheets. I knew I should have done some practice runs but I was too
enthusiastic..

Being a Neandertal, I have to suggest using hot hide glue and a veneer
hammer next time. No clamps required.

And if it begins to lift, you can put it back down with heat and pressure. BTDT.

graham wrote:
dadiOH wrote on 18/11/12 15:54:
graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off
the glued surface. I think that I could probably peel chunks off, a
bit like a nasty bit of far eastern ply.

snip


How long was it under weight

12 hours


and how much flaked off when trimming?

a couple of corners; one a triangle with sides 2cm x 2cm along the
panel edges (this the burr veneer)


Flaked off cross or with grain?
Can't really tell on the burr; on the face veneer the flaking is
predominantly with the veneer grain, having lifted from the edge grain
end. But that's just because my cutting wasn't as gentle as it could
have been - I can lift the edges protruding over the sides (ie. the
veneer long grain) and there's a degree of lifting too (if I continued
the veneer would snap before much came off)

Obviously, the veneer isn't glued solidly. There could be lots of reasons
but if I had to guess I'd guess insufficient glue.

If it were me, I'd try checking that thought by gluing a small piece of
veneer - 2" x 6", eg - on each of two substrates; glue the first as you did
originally, the second with a much more generous amount of glue.

Another though is in the mixing of the glue. The only one of that type I've
used is a dry powder that one mixes with water to a creamy consistency.
"Creamy consistency" is pretty subjective...perhaps you used too much or
little water? I'd check that thought too by mixing up some glue using
varying amounts of water.

Other thoughts include the fact that the glue has a finite shelf life, that
it needs to be at least 65 degrees to cure and that 12 hours is at the low
end of cure time - 18 to 24 is safer.

--

dadiOH
____________________________

Winters getting colder? Tired of the rat race?
Maybe just ready for a change? Check it out...
http://www.floridaloghouse.net

dadiOH wrote on 19/11/12 12:42:
graham wrote:
dadiOH wrote on 18/11/12 15:54:
graham wrote:
Hi All,

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off
the glued surface. I think that I could probably peel chunks off, a
bit like a nasty bit of far eastern ply.

snip


How long was it under weight

12 hours


and how much flaked off when trimming?

a couple of corners; one a triangle with sides 2cm x 2cm along the
panel edges (this the burr veneer)


Flaked off cross or with grain?
Can't really tell on the burr; on the face veneer the flaking is
predominantly with the veneer grain, having lifted from the edge grain
end. But that's just because my cutting wasn't as gentle as it could
have been - I can lift the edges protruding over the sides (ie. the
veneer long grain) and there's a degree of lifting too (if I continued
the veneer would snap before much came off)

Obviously, the veneer isn't glued solidly. There could be lots of reasons
but if I had to guess I'd guess insufficient glue.

If it were me, I'd try checking that thought by gluing a small piece of
veneer - 2" x 6", eg - on each of two substrates; glue the first as you did
originally, the second with a much more generous amount of glue.

Another though is in the mixing of the glue. The only one of that type I've
used is a dry powder that one mixes with water to a creamy consistency.
"Creamy consistency" is pretty subjective...perhaps you used too much or
little water? I'd check that thought too by mixing up some glue using
varying amounts of water.

Good ideas - I shall experiment.
I've used this glue lots, and it was mixed as per instructions and how I
would use it for normal joints. But now that I think about it I recall
mixing it a bit runnier when I was butt jointing 4x2 for the bench top,
I think because I had some notion of the water being absorbed overly
quickly, though it may have just increased working time before all the
clamps were in place.


Other thoughts include the fact that the glue has a finite shelf life, that
it needs to be at least 65 degrees to cure and that 12 hours is at the low
end of cure time - 18 to 24 is safer.

New glue. The tub specifies 6 hours @15 degrees (C), and it was more
like 20 degrees (C) (~68F?).

I shall experiment (and also work out the best route to more pressure
cost effectively)

thanks,
g.

dpb wrote on 18/11/12 16:12:
On 11/18/2012 7:23 AM, graham wrote:
...

I've just veneered a sheet of birch ply (one side ash, one side ash
burr) and when trimming the edges in places the veneer flaked off the
glued surface. I think that I could probably peel chunks off, a bit like
a nasty bit of far eastern ply.

Inevitably I'm wondering what I did wrong.

The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed
spreader then went over it with a sponge roller (apparently it's
important not to have too much glue as it can push through the veneer).
With the veneer positioned I placed it on a piece of MDF and then
stacked a pile of MDF sheets on top.

My guess is that there wasn't enough pressure...

Indeed. You need either a press or at a minimum cauls/clamping. You
need something at a minimum of 50psi which translates to a lot of total
force over a larger surface.

A useful general paper on using--
http://www.djmarks.com/pdf/ureaglue.pdf

--

Thanks for the reference.

I followed up on vacuum presses (expediency vs accruing hide glue &
hammering skills).

I read up at http://www.joewoodworker.com/veneering/welcome.htm but the
price of equivalent looking pumps here in the UK seems ridiculous
(£400), unless I'm looking in the wrong places.

Does anyone know where to get a dry running vacuum pump in the *UK* at a
sensible price?!!


Also, isn't 50psi more than an atmosphere?

rgds,
g.

On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny

graham wrote:

I shall experiment (and also work out the best route to more pressure
cost effectively)

I've never done this but think it should work well and I'll probably do it
someday...

The peoblem in gettring enough pressure is not at the edges - that is easy -
but at the center. Cauls help that, vacuum press is ideal but can be
pricey.

My idea involves dense foam rubber. By "dense" I don't mean rigid, but
squishy, just not real squishy. The sequence, bottom to top...

1. 3/4 ply

2. subststrate

3. veneer

4. cover sheet (brown wrapping paper would serve

5. 3"-4" thick foam

6. 3/4 ply

Clamp along all edges to bring top & bottom ply close together. That will
squish down the foam in the central areas and although the pressure there
will be less it will be even and should be sufficient as long as the width
isn't enough to seriously bow the top/bottom ply.








--

dadiOH
____________________________

Winters getting colder? Tired of the rat race?
Maybe just ready for a change? Check it out...
http://www.floridaloghouse.net

Am I missing something, here?

His project is 250mm X 700mm, or about 10" X 27". There shouldn't be a great problem properly clamping the veneer to the substrate without going through extraordinary means, i.e., special clamping, extending/extended cauls, etc.

Or is he trying to veneer a whole/half sheet of ply, then later cut that sheet into one or more 250mm X 700mm units?

Initialy he says sheet of ply (implying whole/half sheet?), then he uses the term panel (only the 250mm X 700mm unit?).

Sonny

dadiOH wrote on 20/11/12 17:39:

pressure distribution with foam layer


Interesting idea. Strikes me as quite tricky to get foam of the right
density.


Sonny wrote on 20/11/12 18:10:
Am I missing something, here?

His project is 250mm X 700mm, or about 10" X 27". There shouldn't be a great problem properly clamping the veneer to the substrate without going through extraordinary means, i.e., special clamping, extending/extended cauls, etc.

Or is he trying to veneer a whole/half sheet of ply, then later cut that sheet into one or more 250mm X 700mm units?

Initialy he says sheet of ply (implying whole/half sheet?), then he uses the term panel (only the 250mm X 700mm unit?).

I didn't mean to imply the entire "sheet". So panels cut to size then
veneered.

So yes the panel being veneered was 250x700, the next (and largest) is
600x700.

What would you suggest clamp-wise in order to distribute the force evenly?


Sonny

g.

Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing veneer?
(as vacuum presses clearly work!)

g.

On 11/20/2012 6:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing veneer?
(as vacuum presses clearly work!)

g.



Are you kidding. 50psi is easily achievable in a vacuum bag.

graham wrote:

I didn't mean to imply the entire "sheet". So panels cut to size then
veneered.

So yes the panel being veneered was 250x700, the next (and largest) is
600x700.

What would you suggest clamp-wise in order to distribute the force
evenly?

Things of those sizes should present zero problems in clamping, any type
will do. Probably even little spring clamps if you used a bunch of them.


--

dadiOH
____________________________

Winters getting colder? Tired of the rat race?
Maybe just ready for a change? Check it out...
http://www.floridaloghouse.net

tiredofspam wrote:
On 11/20/2012 6:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing
veneer? (as vacuum presses clearly work!)

g.



Are you kidding. 50psi is easily achievable in a vacuum bag.

I've never used one but the word that comes to mind is, "How?". Suck out
every iota of air from the bag and all you have is our standard one
atmosphere pressing, no?

--

dadiOH
____________________________

Winters getting colder? Tired of the rat race?
Maybe just ready for a change? Check it out...
http://www.floridaloghouse.net

Seems some areas stuck down properly and some areas (some edges) didn't. Tap your fingernail on the interior areas to see if you can hear a different sound, a hollow sound, to see if there are interior areas that didn't stick down properly, also. As mentioned, there could be a number of things that have contributed to the problem.

If only those reported edge areas didn't stick down properly, and the rest of the interior areas did, then I would suspect not enough glue along those lifting edges. If there are interior areas that have not stuck down properly, also, then I would suspect not enough and/or a mis-mix of glue. In both of the above scenarios, not enough or inconsistent clamping pressure could contribute to the "non-stuck" symptoms, as well.

Sonny

On 11/20/2012 5:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing veneer?
(as vacuum presses clearly work!)

g.



You have a better vacuum pump that I do.
Best mine can do is 14.7 psi...

On 11/21/2012 7:10 AM, dadiOH wrote:
tiredofspam wrote:
On 11/20/2012 6:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing
veneer? (as vacuum presses clearly work!)

g.



Are you kidding. 50psi is easily achievable in a vacuum bag.

I've never used one but the word that comes to mind is, "How?". Suck out
every iota of air from the bag and all you have is our standard one
atmosphere pressing, no?

No
not even close.

Take a look at some of the web sites on vacuum bagging.
I have a medical grade unit.
Small, and it can crush styrofoam foam easily and some forms of pink
depending on the density. 1 atmosphere won't do that.

I used to use it for model airplanes wings, now I use it for veneering.
I have used it to solve some interesting clamping issues too.

Do I need it? No.. not real often, but since I have it, I would not get
rid of it.

I still have some stock on some nice veneers, just haven't figured out
what I am going to do with them. Some Birds eye maple, quilted maple,
tiger maple , more etimoe, some beautiful walnut burl...

I think when I am up at 30hg I am in the hundreds of pounds per square
inch or more. I don't remember anymore as I don't do it that often.

On Wed, 21 Nov 2012 18:16:59 -0500, tiredofspam nospam.nospam.com
wrote:

On 11/21/2012 7:10 AM, dadiOH wrote:
tiredofspam wrote:
On 11/20/2012 6:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing
veneer? (as vacuum presses clearly work!)

g.



Are you kidding. 50psi is easily achievable in a vacuum bag.

I've never used one but the word that comes to mind is, "How?". Suck out
every iota of air from the bag and all you have is our standard one
atmosphere pressing, no?

No
not even close.

Take a look at some of the web sites on vacuum bagging.
I have a medical grade unit.
Small, and it can crush styrofoam foam easily and some forms of pink
depending on the density. 1 atmosphere won't do that.

I used to use it for model airplanes wings, now I use it for veneering.
I have used it to solve some interesting clamping issues too.

Do I need it? No.. not real often, but since I have it, I would not get
rid of it.

I still have some stock on some nice veneers, just haven't figured out
what I am going to do with them. Some Birds eye maple, quilted maple,
tiger maple , more etimoe, some beautiful walnut burl...

I think when I am up at 30hg I am in the hundreds of pounds per square
inch or more. I don't remember anymore as I don't do it that often.



From West System Epoxy's web site:

"Vacuum bagging uses atmospheric pressure as a clamp to hold laminate
plies together. The laminate is sealed within an airtight envelope.
The envelope may be an airtight mold on one side and an airtight bag
on the other. When the bag is sealed to the mold, pressure on the
outside and inside of this envelope is equal to atmospheric pressu
approximately 29 inches of mercury (Hg), or 14.7 psi. As a vacuum pump
evacuates air from the inside of the envelope, air pressure inside of
the envelope is reduced while air pressure outside of the envelope
remains at 14.7 psi. Atmospheric pressure forces the sides of the
envelope and everything within the envelope together, putting equal
and even pressure over the surface of the envelope.

The pressure differential between the inside and outside of the
envelope determines the amount of clamping force on the laminate.
Theoretically, the maximum possible pressure that can be exerted on
the laminate, if it were possible to achieve a perfect vacuum and
remove all of the air from the envelope, is one atmosphere, or 14.7
psi. A realistic pressure differential (clamping pressure) will be
12–25 inches of mercury (6–12.5 psi)."

http://www.westsystem.com/ss/assets/...Techniques.pdf
--
Jack Novak
Buffalo, NY - USA

On 11/21/2012 7:21 PM, Nova wrote:
On Wed, 21 Nov 2012 18:16:59 -0500, tiredofspam nospam.nospam.com
wrote:

On 11/21/2012 7:10 AM, dadiOH wrote:
tiredofspam wrote:
On 11/20/2012 6:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing
veneer? (as vacuum presses clearly work!)

g.



Are you kidding. 50psi is easily achievable in a vacuum bag.

I've never used one but the word that comes to mind is, "How?". Suck out
every iota of air from the bag and all you have is our standard one
atmosphere pressing, no?

No
not even close.

Take a look at some of the web sites on vacuum bagging.
I have a medical grade unit.
Small, and it can crush styrofoam foam easily and some forms of pink
depending on the density. 1 atmosphere won't do that.

I used to use it for model airplanes wings, now I use it for veneering.
I have used it to solve some interesting clamping issues too.

Do I need it? No.. not real often, but since I have it, I would not get
rid of it.

I still have some stock on some nice veneers, just haven't figured out
what I am going to do with them. Some Birds eye maple, quilted maple,
tiger maple , more etimoe, some beautiful walnut burl...

I think when I am up at 30hg I am in the hundreds of pounds per square
inch or more. I don't remember anymore as I don't do it that often.



From West System Epoxy's web site:

"Vacuum bagging uses atmospheric pressure as a clamp to hold laminate
plies together. The laminate is sealed within an airtight envelope.
The envelope may be an airtight mold on one side and an airtight bag
on the other. When the bag is sealed to the mold, pressure on the
outside and inside of this envelope is equal to atmospheric pressu
approximately 29 inches of mercury (Hg), or 14.7 psi. As a vacuum pump
evacuates air from the inside of the envelope, air pressure inside of
the envelope is reduced while air pressure outside of the envelope
remains at 14.7 psi. Atmospheric pressure forces the sides of the
envelope and everything within the envelope together, putting equal
and even pressure over the surface of the envelope.


The pressure differential between the inside and outside of the
envelope determines the amount of clamping force on the laminate.
Theoretically, the maximum possible pressure that can be exerted on
the laminate, if it were possible to achieve a perfect vacuum and
remove all of the air from the envelope, is one atmosphere, or 14.7
psi. A realistic pressure differential (clamping pressure) will be
12–25 inches of mercury (6–12.5 psi)."

http://www.westsystem.com/ss/assets/...Techniques.pdf


I stand corrected. You are correct as was Graham and dadioh. Somehow I
remembered it differently, I rememberd very high clamping pressures. I
will add to this from that site:

2.1.1 Vacuum pressure
The Hg maximum level is the maximum vacuum level (measured in inches of
mercury) recommended for the pump. This vacuum level translates to the
maximum amount of work effect or clamping pressure that can be
generated. Two inches of mercury (2" Hg) equals about one pound per
square inch (1 psi) of air pressure. (Remember that 1 atmosphere =29.92
inches Hg = 14.7 psi) If you are vacuum bagging a one square foot
laminate, a 20"Hg vacuum will yield 10 psi clamping force or a total of
1440 pounds of clamping force over the entire laminate. If you are
laminating a 4'×8' panel, the same 20" Hg (10 psi) will yield over
46,000 pounds of clamping force spread evenly over the entire panel.

In article , tiredofspam
says...

On 11/20/2012 6:13 PM, graham wrote:
Sonny wrote on 20/11/12 01:24:
On Monday, November 19, 2012 5:38:28 PM UTC-6, graham wrote:
Also, isn't 50psi more than an atmosphere? rgds, g.

1 atmosphere = 14.6959488 pounds per square inch

Sonny


yes, which is far less than the 50psi dpb suggested.
50psi doesn't seem unreasonable compared to normal jointing pressure,
but is completely unachievable with a vacuum press.
So my point really was what is the required pressure for glueing veneer?
(as vacuum presses clearly work!)

g.



Are you kidding. 50psi is easily achievable in a vacuum bag.

Yeah, if you happen to have it under 150 feet of water.

How, specifically, do you propose to get 50 psi using a vacuum bag when
the surrounding atmosphere only provided a maximul of less than 15?

"J. Clarke" wrote in
in.local:

In article , tiredofspam
says...
Are you kidding. 50psi is easily achievable in a vacuum bag.

Yeah, if you happen to have it under 150 feet of water.

Naaaah. 110 feet is enough. :-)

How, specifically, do you propose to get 50 psi using a vacuum bag when
the surrounding atmosphere only provided a maximul of less than 15?

You are absolutely correct. 14.7 psi is the theoretical maximum achievable with a vacuum bag;
in practice, a bit less, maybe 14.5.