gluing large areas

[karl e. hungus]

this would be my first post here. hello. i frequent the carl thompson forum(dont post though) and TB was mentioned there so now ive ended up here.

anyhow a question....

when gluing veneers, accents, and wood with large flat surface area, what is the best technique to make sure you get even pressure across the entire plane?

say im making body pieces, and my plan is one main body piece, a thin accent laminate, and then a thicker top piece(any where between 1/4 and 1/2 inches). whats my best option to make sure i dont get any glue pocket in the center i wont see untill i cut the body piece out?

if im doing just one thin laminate top i know about just using a large sand bag, but for thicker pieces it doesnt seem like it will be enough. do i just need a thousand little clamps? or can i just make one huge jig?

 

[Wood Ascention]

Either a vacuum press or a clamps and cauls.

 

[Jazzdogg]

My vote is for a vacuum bag. Using a torsion-box clamping table and cauls will work, but only if all of the parts are made and used properly.

You can see a variety of veneering tools and materials at the following website, including vacuum bags:

www.joewoodworker.com

 

[Thor]

subscribe.

I have a DIY 1 x10 cab I want to veneer with Brazilian
Rosewood. I am up against the same issues as the OP.

The Len Moskowitz Compact Bass cab.

[Invalid or Expired Link Removed]

 

[Bryan316]

The vacuum bag seems odd. It looks like the edges of the wood would get the tightest hold, but in the middle, there'd be no real clamping force. Am I missing something here?

 

[Jazzdogg]

The vacuum bag seems odd. It looks like the edges of the wood would get the tightest hold, but in the middle, there'd be no real clamping force. Am I missing something here?

At sea level, the weight of a column of air with a footprint of one square inch is 14.7 pounds. If all of the air could be withdrawn from a vacuum bag, the pressure exerted on an item placed in the bag with a footprint of one square foot would exceed 2,000 pounds - plenty of uniform pressure to hold two surfaces tightly together while the glue cures.

In practice, there are several details that need to be addressed, but it's a simple and elegant solution to lots of clamping challenges.

 

[T-Bird]

Hi.

At sea level, the weight of a column of air with a footprint of one square inch is 14.7 pounds. If all of the air could be withdrawn from a vacuum bag, the pressure exerted on an item placed in the bag with a footprint of one square foot would exceed 2,000 pounds - plenty of uniform pressure to hold two surfaces tightly together while the glue cures.

If You halve those numbers it's quite close to the actual pressures/forces. 0.5 bar vac is easy to accomplish even with hand- or foot pumps.

In practice, there are several details that need to be addressed, but it's a simple and elegant solution to lots of clamping challenges.

IMO the best solution and as the shape doesn't matter, as long as there's no sharp pieces that can puncture the bag, also the most versatile.

Exeption would be some glues that rely on humidity and/or oxygen to cure.

Thanks' for the link BTW, with those instructions anyone can make the vac-bag.

Sam

 

[Dirk Diggler]

I guess I'm the only guy just using old fashioned clamps?

They work fine for me and no voids if the glue is spread plentifully and evenly and clamped well. I've actually even used a big slab of wood to hold down an unclamp-able area. Modern glues can do wonderful things.

The vacuum bag idea is interesting but seems like a lot of extra work to me. Plus the cleanup has to be a pain or is it?

Dirk

 

[BassBilodeau]

I agree with Dirk, i use big block of hard wood to have a wide surface of pressure for my tops. Standard clamps does the job. I was considering making a vacuum table but it involve time and money wich i don't have much lately...

I think these two ways of gluing large areas are good, choose the one you are more confortable with.

 

[Jazzdogg]

I guess I'm the only guy just using old fashioned clamps?

They work fine for me and no voids if the glue is spread plentifully and evenly and clamped well. I've actually even used a big slab of wood to hold down an unclamp-able area. Modern glues can do wonderful things.

The vacuum bag idea is interesting but seems like a lot of extra work to me. Plus the cleanup has to be a pain or is it?

Dirk

I can understand your reservations, Dirk. But after several semesters of watching veneering students fall in love with vacuum bag technology, my guess is that you, too, will quickly become a zealous convert when you try it.

I find vacuum bags faster, easier, and far more versatile than any other method I've found; when the proper amount of glue is applied, there's no significant amount of glue squeeze-out to clean up, and if a little glue gets on the bag, it can be peeled off of the surface very easily.

It's great to be able to lay up a 4' x 8' veneered panel, and be able to store everything under your bed when you're done.

If you aren't interested in a full-fledged vacuum bag, you might want to check out an inexpensive skateboarder's kit:

http://www.rockler.com/product.cfm?page=11315&filter=veneer vacuum

 

[Nelson Guitars]

Vacuum bags rule! Once you use one you will never go back.

The biggest problems with gluing large areas is getting the right amount of glue on and getting even pressure across the surface. The vacuum bag handles the second problem and a paint roller handles the first. You really have to use a lot less glue than most beginners realize. I like to use a thin layer on both sides of any material 1/4" or thicker. Veneers tend to swell and move a lot so I keep them dry before sandwiching them between the thicker materials if possible. I also moisten the opposite side of the material with distilled water so that it expands at a similar rate as the glued side will due to the moisture introduced by the glue.

Even pressure is what you want with any glue joint. One big clamp with a caul and two or three grunts when you tighten it is not as good as a lot of little clamps and a caul with one grunt each.


Greg N

 

[Dirk Diggler]

Well that Rockler kit is a lot cheaper than anything I have seen before, interesting. Thanks for the link.
I may have to try that.
Dirk

 

[Wood Ascention]

The joewoorworker DIY venturi system work excellent as well and can be put together for approx. $120 for the pumb then a bag after that. not as cheap as the rockler system but cheaper than a pump. with equal results. Vac. bag as the way to go esspecially for veneer.

 

[tjclem]

That little hand pump system will hold a top as tight to a body as a lot of clamps will?

 

[Nelson Guitars]

Well that Rockler kit is a lot cheaper than anything I have seen before, interesting. Thanks for the link.
I may have to try that.
Dirk

It is the same pump and one way valve that people use as a wine saver. You can find them at wine shops or may have even received one as a gift once and it now lives in the back or the utensil drawer in your kitchen. They are "OK" but do not generate the kind of vacuum that the pumps can.

I still recommend just going to your local appliance repair guy and asking for a used one out of defunct refrigerator. They are usually free that way. You don't need all the fancy valves and such. Just hook it up and let it run.

It's not the size of the pump that holds the top down. It is the air pressure around the bag that is trying to get in. It will most certainly clamp with sufficient pressure and even pressure across that top. Remember that it is dependent on surface area. Small things do not work well in this environment.

If you do get one of these pumps there are some fun experiments you can do. If you make a vacuum chamber (a simple one would be a vacuum hose attached to the lid of a canning jar) and then fill it half full of water you can make it boil at room temperature. Put a marshmallow in the chamber and watch what happens. Grapes can be fun too. It's better though if you have middle school age kids around. They love that stuff.

Greg N