# Laminating plywood sheets



## MrRon (Jul 9, 2009)

I would like to laminate 2 sheets of Baltic Birch plywood (1/2" nom each) for a finished thickness of 15/16". The sheets are 24×48 but smaller sizes could be used. My concern is to get a strong bond. I was thinking to vacuum seal them and wondered if the plastic garment bags that are used for vacuum-sealing would work. I can buy them at HF for about 5 bucks. I've been told that they gradually leak, but for gluing up purposes, they won't be in there for more than a few hours, so leaking is not a big problem.


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## Loren (May 30, 2008)

I'd recommend clamping with bricks or cinder blocks. I don't think
vacuum garment bags are likely to serve well. You need constant
vacuum to veneer with a vacuum bag and I don't think the garment
bags are meant for that. The bags will tear at the corners of
the panels as well unless you make top and bottom cauls with 
rounded corners and edges. Vacuum bags suitable for veneering
are in the 20-30 mil thickness range.


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## MrRon (Jul 9, 2009)

If I make cauls with rounded edges, would the garmet bag work? I just checked the prices and a vacuum bag costs $64 and the vacuum system costs >$350. For less than $5, I'll give the garment bag a try. This is a one shot deal and I will get some cold press glue. How about contact cement?


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## BlankMan (Mar 21, 2009)

I've done it with vacuum setup that of course is made for that, but you've proposed and interesting alternative. Thinking out of the box.

The whole idea behind it is creating the vacuum and let the atmosphere do the work pushing down at 15psi. Don't matter how you create the vacuum just as long as there's a vacuum. For $5 I'd give it a shot. Reinforce the bag on the inside with duct tape where there might be a sharp edge, heck, worth a try.

For a project I've been thinking of that won't fit in the bags I have I was going to buy a 6 foot bag when the time came, now I might try this myself.

Question being, can you draw down enough of a vacuum and will it hold that vacuum. My vacuum pump setup has a tank just like a compressor and cycles to hold the vacuum I set it to when in use. But even if you would have to draw the vacuum down periodically, big deal, mine does that too just automagically.


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## BlankMan (Mar 21, 2009)

And you can do the "vacuum systems" on the cheap. I originally got the Vac-U-Clamp CD-1001 kit from Woodcraft when they had a 10% sale and I think I had a gift card to help.

But, I then wanted better so I looked around. American Science & Surplus is near me and they were always selling vacuum pumps so I decided to check out if they where any good. Turned out they were, real good. So I missed the boat there but picked one up on eBay, like this:










That's Thomas pump in the $400-$500 range new. There's some on eBay now for $65 Buy it Now, even lower in bidding. A lot of the other stuff you need you can get from Joe's Veneer Supplies. Do it over time as you need stuff, that's what I then did, it's easier on the pocket book.


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## DS (Oct 10, 2011)

Baltic Birch is actually 12mm, so your resulting panel will be 24mm. (0.945")

If you have a vacuum bag setup then great. If not, clamps at the edges and weights in the middle usually will do the trick.

The garment bag is ok, except what will you draw vacuum with? A vacuum cleaner will NOT draw enough to be significant. (Low pressure/high volume vs. what you need, high pressure/low volume)


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## BlankMan (Mar 21, 2009)

Yeah a vacuum cleaner might only be able to pull 1" Hg and I think my pump pulls around 25" so that may not work.

But I think I remember Norm doing it one time with a hand pump. Brutal but it worked. Wonder what that thing pulled it down to.

With that in mind I wonder if the seams of a garment bag would hold at 25".


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## crank49 (Apr 7, 2010)

I built my entire workbench out of laminated 3/4" plywood (7 layer cabinet ply). 
I glued with Tight Bond III and screwed together on 8" centers; clamped the perimeter.
Worked perfectly. My top is 3-1/2" thick.
But there are screw holes in it; maybe a problem for what you are trying to do?

If you are set on using vacuum you can buy a vacuum pump at HF for $105. 1/2hp, 3 cfm I think.










You will get a lot less pressure with a shop vac compared to a vacuum pump.

A shop vac will only pull about 60" to 90" WC which is about 2 to 3 psi. 
A vacuum pump will give you about 15 psi.

Over a 4' x 8' sheet the total pressure is about 70,000 lbs with a vacuum pump;
about 9,000 to 14,000 lbs with a shop vac.

Contact cement will work but is a much more flexible bond and doesn't require vacuum or clamping.
Contact cement needs to be virtually dry before the sheets are brought together.
On a large surface like this you might need to put the sheets together on the floor and then roll them together with a heavy flooring roller. Overall I just don't think this is a good method.

Why not just buy a sheet of 1" baltic birch plywood?


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## BlankMan (Mar 21, 2009)

Michael, A shop vac will only pull about 60" to 90" WC? I measured mine, my 4.5HP big one pulled 8" and the 4.5HP Hangup pulled 14". That was with airflow, not blocked now that I think about it, so you might be right, never thought of that. I don't have anything that will measure WC that high.

If a vacuum pump pulled 15 psi that be 30" Hg, most affordable pumps I know of struggle to hit 25", mine included, pretty much its limit. And it's not a cheap pump. Pulling 15psi, 30" Hg, that be a perfect vacuum. 12.5psi/25" Hg is what is considered attainable from what I've read.

That little one you pictured says it draws 10 pascal, that's 0.00295" Hg. So ok maybe they meant 10 kPa but still that's only 2.95" Hg. And that's only 1.5 psi thus a clamping pressure of 6900 lbs on a 4×8 sheet. So if a shop vac can pull 3 psi looks like it be a bit better.

I think a realistic number is around 57,000 lbs with a good vacuum pump on a 4×8 sheet.

Still can't beat a good vacuum pump.


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## crank49 (Apr 7, 2010)

I have the same pump as the one HF sells, but I bought it 14 years ago from a jewelery manufacturing supplier. I paid $450 for it back in 1998. Don't know if HF has them made from old designs or what but mine will pull 29" mercury on my guage. That will make water boil at room temperature.

The HF unit might not be produced to the same quality standards as my old one was and I can't say it will produce the same pressure, but as you pionted out, even a whimpy pump will outpull a shop vac.

By the way, I have checked the pressure on shop vacs with a homemade manometer. You just need some clear hose and a ladder and tape measure.


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## BlankMan (Mar 21, 2009)

Michael, LOL Doh!


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## Dal300 (Aug 4, 2011)

For an air bag you might consider buying a single bladder water bed mattress. Used would be the best.

I have a couple of old refrigerator compressors and a couple of old 10 ton A/C compressors. Hopefully it would be easy enough to use those, either singly or in parallel to create the needed vacuum.

Come to think of it, you can buy a single bladder air mattress for about $30. I wonder if that would be sufficient?


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## DS (Oct 10, 2011)

If you're really set on making a bag, I've had lots of success with 10mil vinyl that you can buy at a fabric store and double-sided foam tape from Home Depot. I used a mag wheel valve stem with the core removed and large washers to reinforce the mating to the bag.

joeewoodworker dot com has a lot of resources too.

good luck


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