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gluing two sheets of birch ply

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Forum topic by Pabs posted 03-25-2019 06:03 PM 699 views 0 times favorited 28 replies Add to Favorites Watch
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Pabs

272 posts in 3786 days


03-25-2019 06:03 PM

hi, I need to glue two sheets of Russian birch ply (3/4, well a little less as it’s metric)
sheets are about 57”by 40”. I need these to glue well and flat. Ideally I don’t want to use screws.
what’s the best way to clamp this and ensure flatness?

-- Pabs


28 replies so far

View bilyo's profile

bilyo

611 posts in 1435 days


#1 posted 03-25-2019 06:58 PM

Unless you have the need for water resistance, I don’t think the kind of wood glue you use matters too much. However, I would use a long nap roller to apply it on both surfaces before putting them together. This will insure quick and even application. The clamping part is perhaps the most difficult. Ordinary clamps won’t reach to the center. A vacuum bag might be the best if you have one. The first thing is to find a flat level place to leave it while drying. If I were doing this, I would need to lay the glued up sheets on my carport floor and use multiple plywood or hardwood cuals to distribute the load. Then I would place multiple weights, like concrete blocks or bricks, all over it to apply the pressure needed until dry.

View John Smith's profile

John Smith

1758 posts in 495 days


#2 posted 03-25-2019 07:01 PM

find a perfectly flat place on your garage floor
or in the kitchen at night. glue the two pieces together,
place newspaper around the edges to catch any squeeze out.
and put as much weight as you can find – starting in the middle
and working outwards so you can disperse the glue evenly.
concrete blocks, bags of sand or cement, buckets of water, etc.
a few screws here and there will prevent the boards from slipping.
remove the screws after it is ready. (4-8 hours). overnight is best.
that is how I build heavy duty boat transoms.
no clamps or vacuum bags required.

.

-- Failure is proof that you at least tried ~ now, go do it again, and again, until you get it right --

View Richard's profile

Richard

11274 posts in 3365 days


#3 posted 03-25-2019 10:19 PM



find a perfectly flat place on your garage floor
or in the kitchen at night. glue the two pieces together,
place newspaper around the edges to catch any squeeze out.
and put as much weight as you can find – starting in the middle
and working outwards so you can disperse the glue evenly.
concrete blocks, bags of sand or cement, buckets of water, etc.
a few screws here and there will prevent the boards from slipping.
remove the screws after it is ready. (4-8 hours). overnight is best.
that is how I build heavy duty boat transoms.
no clamps or vacuum bags required.

.

- John Smith

I agree with John.^^^^^^

-- Richard (Ontario, CANADA)

View ArtMann's profile

ArtMann

1336 posts in 1148 days


#4 posted 03-26-2019 12:46 AM

That solution looks to be about 100 pounds per square foot to me. Theoretically, that isn’t even close to enough but if it works then it obviously is enough.

Here is the way I clamped up a router table I made out of 2 layers of MDF. I laid out a series of short 2X4 pieces across the top of the MDF stack. I used two 4X4 pieces about 3 feet long laid across the top of the 2X4s parallel to each other and perpendicular to the 2X4s. I laid a third 4X4 spanning the first two in an “H” pattern. I took a 4th 4X4 that was within one foot of the ceiling beam height in my shop and used it vertically with a hydraulic jack to apply downward pressure on the horizontal 4X4s. I figure I evenly applied between 1000 and 2000 pounds of force to the surface of the MDF. The results were excellent and there were no gaps between the MDF sheets. Of course, that means you need a very flat section of floor.

I hope that made sense. The basic idea is to use a hydraulic jack and heavy timbers to create more force than you can get by stacking bags of sand or similar dead weight on the surface.

View CWWoodworking's profile

CWWoodworking

369 posts in 511 days


#5 posted 03-26-2019 01:55 AM

Isn’t Russian birch ply notoriously NOT flat?

View Dark_Lightning's profile

Dark_Lightning

3415 posts in 3441 days


#6 posted 03-26-2019 03:48 AM



Isn’t Russian birch ply notoriously NOT flat?

- CWWoodworking

Straight off the stack I’ve gotten it pretty much dead flat. But it has to be used reasonably soon. It warps less than the green DF ply you normally get at a BORG though.

As far as thicker BB ply goes, when we made models for RCS work I seem to recall that we had some pretty thick (>3/4”) pieces, 1”, IIRC. But then we also got it in 5’ X 10’ sheets instead of the 5’ X 5’ you typically see.

-- Random Orbital Nailer

View therealSteveN's profile

therealSteveN

2383 posts in 906 days


#7 posted 03-26-2019 06:09 AM


- John Smith

Whoever said a picture is worth a million words, musta seen that pic John.

That’s how I do it when I don’t use screws. Generally when I am laminating plywood though, there is a show face, the other side is just not a factor, so screw holes are where only 2 year old kids can see them. I give them candy to shut up….....

-- Think safe, be safe

View Fred Hargis's profile

Fred Hargis

5459 posts in 2825 days


#8 posted 03-26-2019 10:33 AM


That solution looks to be about 100 pounds per square foot to me. Theoretically, that isn t even close to enough but if it works then it obviously is enough.

- ArtMann

I’ve tried to apply veneer using weights like that and it’s never worked…because of what Art said. It’s almost impossible (at least with veneer) to get enough weight to force the 2 surfaces together. While I personally don’t like this, I can’t help buy wonder if contact cement would be a better choice. Whatever you try I’d bei nterested in the approach and how it turns out.

-- Our village hasn't lost it's idiot, he was elected to congress.

View John Smith's profile

John Smith

1758 posts in 495 days


#9 posted 03-26-2019 11:24 AM

the nay-sayers will have a field day on me if I showed how I used the same
technique to glue much larger pieces together with the expanding urethane
Gorilla Glue – I used over a thousand pounds of sandblasting sand for weight
and forgot to put paper under the edges to catch the squeeze out. . . . .
it was a total catastrophe. (I did it in the evening and let it set overnight).
not only was the floor not flat at that particular spot – the squeeze out glued
the panels to the floor and to be cut off with a sawz-all. . . . . total muck up.
you learn as you go – and you pay your dues – no matter what your trade is.
and as the saying goes ~ there is no free lunch.

personally – I would not want to jack up my roof with a hydraulic jack.
I would however, entertain the thought that if it were a small(ish) panel to put
it under my 5,000 pound van and put the jack between the frame and the panels . . . .
with the tires 1/16” off the floor, you know about how much weight you have
applied. with contact cement, you only have to apply severe pressure just one
time for a second or two over the whole surface and it’s done.
all kinds of ways to skin a cat – just depends on what works for you in your circumstances.

.

.

-- Failure is proof that you at least tried ~ now, go do it again, and again, until you get it right --

View gwilki's profile

gwilki

284 posts in 1806 days


#10 posted 03-26-2019 12:18 PM

I’ve used clamping cauls with very good success and using them means I don’t depend on my floor being perfectly flat.

-- Grant Wilkinson, Ottawa ON

View Tony1212's profile

Tony1212

311 posts in 2067 days


#11 posted 03-26-2019 12:35 PM

When building my workbench, I laminated four 24”x60” BCX sheets (very much NOT flat) to make up the thickness. I didn’t want to use screws since I was worried I’d hit them when drilling the dog holes. But I knew I was putting a 1/4” plywood sacrificial top on it.

So I put them on the ground with the bottom two pieces cupping up and the top two cupping down, put a couple screws in the two adjacent corners and drove the front wheels of my car onto them. Still not 100% flat, but pretty darn close. The screws were only there to keep them aligned and allow the other edges to move while they flattened out. I removed them the next day, after the glue had dried.

-- Tony, SW Chicago Suburbs

View DS's profile

DS

3114 posts in 2752 days


#12 posted 03-26-2019 01:52 PM

Then there is how the pro’s do it;

Just sayin’...

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Pabs's profile

Pabs

272 posts in 3786 days


#13 posted 03-26-2019 02:34 PM



Then there is how the pro s do it;

Just sayin …

- DS

sounds like the best option, I’ll order one this afternoon :)

-- Pabs

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Pabs

272 posts in 3786 days


#14 posted 03-26-2019 02:39 PM

after reading all these options I may simply do this

I have a table that is smaller than the sheets I want to glued and the table is pretty flat. I would center the sheet on it having a good 10 inches all around overhanging the table. I would use a series clamps on the edges and for the middle of the sheet I could simply use a combination of screws and weights. the back side will never really be seen anyway (it’s a headboard for a bed). I can remove the screws and fill in the holes before finishing as well. I think this might be the easiest way. I can use a few straight pieces on top and clamp across to make sure the sheets are tight to the table .

-- Pabs

View ArtMann's profile

ArtMann

1336 posts in 1148 days


#15 posted 03-27-2019 01:32 AM

If you have the option of using screws, that will be by far the most effective clamping method. Just use drywall screws on a grid pattern and drive them with a drill driver or impact driver without pilot holes. If they won’t be seen, just leave them in place. I promise not to tell anyone.

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