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Howdy,

Couple questions for those of you making double sides:

I have been making double sides with Unibond 800 using an outside mold an a semi-rigid inner clamping caul and a makeshift warming "oven". Works fine but it takes 9 million clamps and is unwieldy.

Do any of you use a male mold with a vacuum bag? Are you able to get a really nice flat outer laminate after gluing, or does the outer laminate need to be sanded flat? Obviously with an inside mold the pieces come out quite nice... I can't imagine anyone is using an inside side-mold with a vacuum bag but I have to ask...

What are your thoughts to an inner layer of flat-sawn material and a quarter sawn outside lam? Does anyone have any evidence that this is more crack resistant than two quarter-sawn pieces laminated together?

For those of you using Unibond 800. What ratio's are you using? How thick do you put it on? I haven't had any problems at all but I am wondering if I am using more glue than I need to...

Thanks, Peter Z

"I have been making double sides with Unibond 800 using an outside mold an a semi-rigid inner clamping caul and a makeshift warming "oven". Works fine but it takes 9 million clamps and is unwieldy."

I was sorta impressed with Bogdanovich's method. It looked like it uses fairly few clamps. Quite a lot of vac bagging is no picnic either.

"Do any of you use a male mold with a vacuum bag? Are you able to get a really nice flat outer laminate after gluing, or does the outer laminate need to be sanded flat? Obviously with an inside mold the pieces come out quite nice... I can't imagine anyone is using an inside side-mold with a vacuum bag but I have to ask..."

I can imagine it, and I would try it myself. Half the advantage of any molding is transferring the surface of the mold to the visible surface of the end product. What problems do you anticipate?

"What are your thoughts to an inner layer of flat-sawn material and a quarter sawn outside lam? Does anyone have any evidence that this is more crack resistant than two quarter-sawn pieces laminated together?"

I think that any time you attach a piece of wood with greater split resistance than another to a lamination, you will get greater split resistance. Flat sawn of some woods might apply. Some woods, like elm, sitka, etc... are known for their split resistance. What I don't like about flatsawn is the dimensional stability. I see that as introducing a stress. If your sides have no straight lines, it may not show, but I just wouldn't want it in there. What I would try would be interior woods with more run-out on the face grain. If you can get 1-20 degrees off center, opposed, for wood on two internal lam layers, that should be great.

What we are really moving towards is plywood. A 90 degree layer would make a lot of sense. There is an increasing tendency to use processes that start with a structural upgrade, and then working out how to get, or sell the tone later. Plywood is where that should be heading, but the fact that plywood is regarded as a cheap alternative (not the case if you make it yourself) undermines what is just common sense.

One option with two veneer plies at 0/0, is to introduce a very light fabric scrim in the neutral axis, and you don't even have to mention it. Why is it a stroke of genius to put a carbon layer in a brace, or a rod in a neck (normally in the wrong place), but a 90 layer in a side is somehow looked down on.

I use epoxy for all this stuff. I don't know about U 800. Normally the thinnest wet layer you can get on both surfaces, is the gold standard, but I haven't used that stuff. I used a ton of Weldwood, urea, until I had a massive outbreak of dermatitis.

I am working on 5 insturments that all have laminated sides. All with sliced veneer. I use an outside mold with unibond in the bag. The first few I did, I used the mix that gave the fastest dry time but now do the mix with the slowest because it seems best to wait overnight anyway. It is a trick to pull/push it 'down' against that inner ply but I can make it work. I use breather mesh on the inner ply to help pull it. I had a few areas that did not make a perfect fit but I am going with them, because the outside is perfect. I made a 'perfect inner mold & put a bunch of coats of urethane on it but use waxed paper too.
I can't find it now & maybe it was on this forum but I saw a mold for a cello or base builder who with his outside mold ran neoprene around the perimeter & uses a single piece of vinyl or poly & it wouldn't take more than a few seconds to pull vacuum.
Some of mine are plywood with an inner ply at 90 de.
Some are running paralell, most with different species.
I've done male molds for other furniture stuff & the outside piece always seems to have some irregularitys, but for furniure I just make it work anyway,
I also use "titebond original extend" glue a lot now.
Daryl, at vacuum systems did some testing & found it was almost as rigid as unibond. It has a 15 min open time & non stress joints can come out of the clamps in an hour.
I'll keep looking for the cello side clamping mold. let me know what you try, me, I'm addicted to vacuum bagging.
MM

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Mike McNerney

I do have a lot of experience with vacuum bagging, just with more exotic composites (carbon/kevlar/fiberglass/epoxy/foams, etc..), not guitar related stuff - so I am not intimidated by it and feel that it would ultimately be easier and result in a better finished product than one that relied on clamps. It just seemed to me that given the shape of an inside mold, it would be harder to get the bag to conform compared to a male mold.

I would like to stick with Unibond. Seems better than the epoxies I have used (different West formulations, System Three...) for hardness of glue line and resistance to softening with heat. I find the U800 and epoxies equally toxic which is a bummer.. As far as an inner carbon layer or something. I'd love to not to do that. Would force me to use Epoxies again... As far as titebond goes. It may work fine but it is not recommended for stressed/curved laminations and has a shorter working time.. So I am going to stick with what I am using now.

Mike - what kind of bag are you using Polyurethane or Vinyl? Do you know how thick the bag's material is? Did your mold look like Bogdanovich's?

One of my hopes was to make/buy a vacuum frame-press and use it with male molds so I could make two sides at once (cuttaway and non-cuttaway). If anyone out there is having good luck with what comes off a male mold, I'd love to hear about it...

As far as making 0/90 laminations. I agree that it would be super crack resistant, but how much crack resistance is necessary? Seems that if you dropped a 0/90 side laminated guitar, the sides might stay intact, but the top or back might then crack.. I just want a structurally balanced package, not overkill.

So does flatsawn + quartersawn (grain running same direction) yield any desirable crack related improvements over quartersawn + quartersawn?

Thanks, Peter Z

I don't really 'know if flat sawn with quartered would yield a more crack resistant side. I am also making some of these with laminated backs. I have tried 0/90 and 0/15. I am a beginner guitar builder so my main motive for laminated construction is to build an affordable (approx 75 bucks) BRW veneer guitar before I use a 1000 buck set.
Are you using sliced veneer or resawn 'solid material'?
IMO sliced is weaker cross grain than resawn of equal thickness. That's why I am going with 0/90. If you are doing resawn 2 ply side like Somogyi then I'm not so sure the bag would pullit enough unless the 2 prebent pieces were extremely close in nesting together, just a wild guess but say .005.
Try to find the cello side mold. It would absolutely be the best way to go.
MM
You'll have to send me a picture of the Bogdanovich mold, I haven't seen it.
I did my sides in my original vinyl bag, 25 yrs old.

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Mike McNerney

My sides are made up from resawn, thicknessed guitar stock. I prebend on my Fox style bender and get things nesting very well. From my experience, you can apply a lot of force with vacuum bagging. So much so that in the past I have actually crushed lower density (non-guitar) items - like you sent them to the bottom of the sea! Pretty amazing - although a bummer at the time. I guess some tests with my inside mold would let me see if the vacuum pressure is sufficient. My guess is that from past experiences, it will be.

Peter Z

You can't get more than 11-12 psi vacuum bagging. Glue manufacturers recommend more like 175 psi.

Brian Burns vacuum laminates sides with an inside mold. He adds a "shoe" in the waist to get more pressure there. IMO this is a job for clamps.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Agree with Howard, clamps much mo better.
Uni-bond I like to mix at 1 to 4. I do this by volume. Since it has a huge amount of latitude in mixing (from 1:3 to 1:6) I just shoot for 1: 3.5to 1:4. Never had a single problem.
L.

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

Howard,

175psi would mean that you would need 40 Medium sized Bessey clamps (completely maxed out) to do a side! That seems quite excessive. Are you certain that's not 175 pounds per square foot? If the PSI figure is correct, that would seems to mean that vacuum veneering/laminating wouldn't be possible - obviously it is, so where's the disconnect?

Link: Thanks for the ratio info.. I have been going thicker than that (with no problems) but will give a thinner mixture a try on my next go around..

Regards, Peter Z

I think the trick with a male or outside mold (which is what I prefer) is to size it right and use a thin non-corrugated card board called news board on the cauls. It gives just enough to ensure even pressure but isn't too soft so you get a nice fair outside surface on your finished product. Plus it absorbs glue and keeps any bled through or squeeze out localized and there for easy to clean.
L.

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

Link,

How thick is the news board? Right now my clamping caul is made up from laminated mahogany with glue blocks to spread the load across the width. So you're saying this news board is a sacrificial layer that goes between the caul and the laminates that compresses a little bit helping everything get seated (to make up for inconsistencies in the semi-rigid clamping caul)?

Peter Z

Yes, and it becomes even more important with a rigid clamping caul for the reasons you stated. You can get it in 3 different thicknesses. They call it regular, double thick, and triple thick. I usually use the double. Art supply stores is where you find it. I would guess the double is about 3 /32". It is handy stuff. Spray adhesive it to scrap 3/4" ply and have it on hand for any kind of clamping caul. Just cut up what you need when you need it. It is like the card board that you find on the back of writing tablets. I use it for all my veneer work and bent laminations.
L.

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

You don't need what the glue manufacturers recommend. There are very few situations where you could get that much pressure without hydraulic presses--essentially you would have to put screw clamps right next to each other over the whole piece of work. Fortunately we do fine at lower pressures. But lamination seems to me to be a place where you want as much as you can get as a practical matter. I use an inside form with 12 cauls, two clamps per caul, tightened as hard as I can get them. So I'm getting maybe 35 psi. Three times what you can get vacuum clamping.

I think the glue manufacturers are thinking production shop with perhaps not the most perfect joints. They give somewhat lower figures for softwoods, probably because they are more compressible. One thing I do take from this, though, is that the starved joint from overclamping is a myth. You can starve a joint, but not that way.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Again +1 on what Howard says.
This is especally true if you wet out both surfaces with glue

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

Point(s) taken. Thanks Howard, Link and Mike. I appreciate the inputs..

Regards, Peter Z

I don't think double sides are very easy to press together unless they are pretty thin. I really don't think getting them to mate perfectly would be reproducible enough for me. I think I would go with the clamps and cauls.

I make laminated guitars like gibson ES and use rotary cut veneer. For this I find it easier to do the bent lamination technique with the bag outside the form. Putting a guitar form inside a bag and expecting it to conform without tenting in some areas is a leap of faith. I guess you could ideally use two bags, one for pressing the laminates together and another big one to get them to conform to the shape of the guitar mold. A bag inside a bag. You could even add a bladder to hold up a flimsy form.

Vacuum pressed joints are fine when the wood is thin. I think what Howard is referring to would relate to thicker solid wood.

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Ken