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I have a vacuum clamp jig, and was wondering if any of you have successfully used this method for a set of laminated sides . Just watched the bogdanovitch DVD on laminated 3 pce sides 2 .022 yellow cedar sides laminated to .075 EI rosewood. His method uses a rigid MDF side and a laminated mdf bent side with 16 mdf cauls to glue the laminates together. My question, is there a way to do this similiar process in a vacuum bag with a caul?? or is just too difficult to do in a vacuum bag, your thoughts please ?? I have successfully laminated 2 piece sides for guitars and ukes, but have not tried a 3 piece lamination, which would have to be done quickly before the glue sets.

Not really. Use the right glue and you will have no problem. I would use a Urea Formaldehyde type glue of which Uni-bond is my favorite. If you are using a bag you will have to clamp up your veneers in a sandwich in the bag and then bend the whole thing on the form. If inside the bag I think your form would be too tall. I suppose you could make a special bag to do it. It is so easy to make a two part mold and achieve more clamping pressure why bother with the bag.
L.

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Cut to size.....Beat to fit.....Paint to match.

Thanks for the info , Have never used a veneer bag,

I've done some vacuum bag veneering of flat panels etc.

It is theoretically possible to use a breather mesh instead of a caul assuming you have some way to keep things in place while the bag sucks down. Big emphasis on theoretically.

joewoodworker.com has lots of good info on vacuum bag veneering, clamping, etc.

Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

The problem is the stretch of the bag. If one made a rectangular bag with box type top and bottom (instead of a envelope style) and put the breather mesh on the sides of the mold it would work. But again with more clamping pressure and so easy to make why not a mold with cauls or a double mold.
L.

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Cut to size.....Beat to fit.....Paint to match.

Somewhere I saw an article and photos of using a vacuum bag for laminating sides. Maybe it was a post by one of our members.

If the mold sides and bottom are scored, such as 1/16" deep kerfs several inches apart, the air can move all around, so a box to suspend the membrane is not necessary. The mesh may still be advisable.

Using clamps and cauls has worked well for many. However, it is often not true that you get tremendous more pressure everywhere with clamps. It is true that you get this locally where the clamps are applied. It may also be true that mathematical models predict high pressure in between clamps. However, how many of you have clamped boards and noticed that the twisting of the clamp may actually spring open gaps in some places?

That is why you use cauls, to avoid all the problems you mention. You don't need mathematical models, as they say, "this isn't rocket science." Woodworking 101.
Use a caul tall enough to distribute the clamping forces. Clamping forces are a cone of roughly 45° from the point of contact. Get some overlap. Just eyeball it, no big deal. Anyone who has done much bent laminating knows clamps work much better than bagging if you want the smallest glue lines. That translates into more pressure applied. A lot of veneer work was and has been done with out bags. I do like my vacuum system but mostly for flat work. I have done plenty of flat work with a press as well.
L.

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Cut to size.....Beat to fit.....Paint to match.

What exactly do Rocket Scientists use as a cliche when they want to express that something isn't all that complicated?

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John Mayes
http://www.mayesluthier.com

I laminate 3 piece sides in a vac bag. I use sliced veneer, which of course bends cold & offers almost no resistance. The inner & outer layers approx .025 & the centre around .040. with the centre running 90 de. to the others.
I have also laminated a 4 ply with all running in the same direction.
I do all this with a female mould.
It is a bit of a trick getting the bag snug but once you get it close the pump will pull it down OK. You have to stop the pump at times & pull the bag in to the curve.
Breather mesh is a must & I run it down the full length of the curve & over the edges of the form. the form has lots of chanels over the rest of it's area for easy air evacuation
Unibond 800 is probably the ticket because it has such a long open time, and it is an extremely ridgid glue line. Although I have also succesfully used titebond original extend.
My pump takes a good 5 to 8 minutes to pull this set up to 25HG.
I saw somewhere on the net a cello builder who has a simillar set up. But of course those sides are 3 pieces. He had a single piece of plastic over each that sealed itself against a neoprene perimeter.
I would like that link again to study it closer.
MM

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Mike McNerney

It ain't lutherie!

What exactly do Rocket Scientists use as a cliche when they want to express that something isn't all that complicated?

Something about brain surgery????

Thanks mike for the explanation, do you get your veneers in Ottawa, ?? I have an older vacuum clamp that pulls 25 hg that can be retrofitted to accomadate a bag. I believe it was purchsaed from a co.in Mass. I know of several veneer suppliers certainly woods ?? constantine?? and LMI for veneers . Are there others. in the usa ?? I/m just finishing up a 4 piece laminated mdf caul to glue the 3 piece sides together. Cheers

Certainly woods is the best I have found. You can can get BRW easily from them & many others.
I have tried .062 maple, walnut & sanded it down for my middle layer.
Also B & B rare woods, in Colorado I think, also has slightly thicker BRW.
MM

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Mike McNerney

Thanks Mike checked out certainly, but one needs to make a large order. I am looking for thinner stuff e.g. yellow cedar .022. I got some solid YC from a mill in courtenay/comox van island abt 10 yrs ago., but forgot the supplier/s name . Will check out B&B. Ps am 1 yr older than you grew up in Mtl and spent 20 yrs in van, where I learned cabinetmaking hahah cheers and thanks for your help ernie

Simple vacuum bag setup.

Place tape on your part at several locations with fiberglass tape on the outside of your parts after you glue them up. "Reverse" ( important ) the tape........ so that the sticky part is out........ then use nylon screen ( porch/widow screen ) and cover the part in just enough material to cover it entirely ( ends can usually be left uncovered unless there is a reason to cover them ). ( Lowes..Home Depot... carry this stuff and a large roll is fairly cheap) Allow the reversed tape to hold it in place. The nylon screen serves the same function as the expensive breathing material that the bag companies recommend.

Now place in your vacuum bag or on mold or not( depending on part ) pull vacuum allow enough time remove from the bag and remove the screen.....( cut, tear, whatever, this is part of what is so nice......... it now is a disposable item....... sometimes we are able to reuse the material but at the price doesn't really matter )

Works every time with no problems........ been doing this for 20 years or more on all sorts of wood working parts and pieces including stacked window and door casings, spiral stair cases, bombay drawers, s- curves for grand father clocks and yes guitars and more.

Kevin Waldron

Kevin my mold for the sides is aluminum the caul to glue the laminate sides is .360 mdf 4 pcs of .90 mdf bent into half shape of a guitar side . Can I use the caul to glue the laminates with your method ?? if so were can I get a bag ? or make one ? I bought a vacuum clamping jig 10 yrs old,it is a small burgundy box with a foot switch that can pull 25 hg.

Best way is probably send you to one of the sites.......... I have no affliation........... but you should be able to get some ideas, from this site.

http://www.qualityvak.com/speciality-system.html

Kevin

thanks kevin these are the people I got my vaccum clamping eqpt from