Laminating multi-ply acoustic guitar backs and sides [Pictures] - created 12-21-2007

parker, jeff - 12/21/2007.12:36:44

It is difficult to tell from the discussions I have read as to how many luthiers are using laminated backs and or sides. Whether you call them double sides or laminations. Also there is mention of using vacuum bagging for clamping which is expensive.So I will post my low tech solutions. For the sides I use a regular side and one piece or all wood two ply veneer. This is available in lots of woods but what is stocked in Anchorage is birch cherry or oak. I have been using powdered veneer glue as it dries hard and I think helps in the tone. For clamping I use a mold similar to a bending mold and for the clamping pressure I use a strap. I found you have to add pieces of hard wood to provide an even pressure across the sides or they can curl. To hold them in place while setting the strap I epoxy glued them to a piece of canvas.Jeff

For the backs I have been succcesful in using a go bar deck.

This is a back with one lamination and holds it 15 foot radius very well.It might help to think of the laminate as one very wide thin brace.jeff

Cool! Do you have a pic of the back in the deck getting clamped? What kind of caul do you use, and where do you keep the 500 go-bars necessary? ;-)

I am not too familiar with the laminating method. What thickness of veneer do you use?

I have been using just scraps of wood.I start in the center and work my way out. Today however I have been making a caul by using a couple of round boards and filling the space with automotive bondo. I just laid wax paper in the dish radius mold spread in a thick layer of bondo and clamped the flat disks on with the go bars.the will probably be a liitle sanding to do before its first use. Here is a pic with the back in the go bar deck. Jeff

As you can see I use fiberglass rods I cone one end and bevel the other. The bevel end goes down usually, this prevents the rod from wanting to spin and the cone end digs in the top slight to prevent splipping out. I sanded the rod shapes on a belt sander.

Jeff;

Merry Christmas

J

I looked up the all wood veneer It measures .040 inch net so two .020 layers. I was going to put in link but am not sure that is legal, For more information you can do a google search for Allwood two ply veneer. Jeff

Hi Jeff,

For the back plates I align the leaves and press between two pieces of melamine coated particle board. Again I use wax paper between the wood and veneer. I press them flat and work with them as I would a regular back set.

I orient the leaves to to give me book matched backs and sides. Using matched leaves gives the appearance and some of the properties of conventioal materials. The back and sides of completed instruments will crack if subjected to extremely low humidity levels (same as conventionally built guitars).

If you can find "kerf core" material it may save you some trouble with your molds.

Thank you for the comments. When I am in the SF Bay area I visited seveal hardwood lumber yards. There were piles of exotic veneer which looked very appealing. I even brought home some jatoba thinking I would line guitars with it. Maybe I should make a jatoba guitar!

I used to use epoxy to laminate, a hold over from boat building days, I read somewhere that in vibrating instruments softer or more flexible parts absorbs some of the energy and thus dampens sound. So I switched to a glue that dries hard for the backs and sides. I still use epoxy on the soundboard because it is flexible. Have you any thoughts on this? Jeff

Hi Jeff,

The cured sides hold their shape quite well and ring like a bell when held at one end and tapped at the other.

But what is this powdered veneer glue you are using?

I use ultra cat from Joe woodworker. If you google this you find a wealth of information about veneering and vacuum forming. The glue is a plastic catylized powdered urea glue. Cheaper than epoxy and water cleanup (sortof). Jeff

Recently I have incorporated graphite fiber cloth as one of the layers, but generally I do not do this.

Clay, what's your rationale for the carbon fiber cloth? I've got some of that carbon fiber cloth left over from some solar human-powered vehicle projects some years ago and that sounds like a cool way to use it up.

Hi Jeff,

Hi Jeffrey,

I am building a "takedown" guitar and in addition to the neck disassembling easily I want the back and sides to be semi-tough. I think the veneer-cloth- veneer combination will give a traditional look and good crack resistance. It might also allow you to use otherwise fragile veneers (burls) that structurally couldn't stand alone. Plus it has that hi-tech vibe.

Plus it has that hi-tech vibe.

Exactamundo. I especially like the idea of using burl veneers, though. Are you gluing up one wide side and then cutting it or are you gluing both sides separately? What I'm wondering is how much tooling you're doing to the carbon fiber once your sides are laid up and set? It can be murder on tools.

Jeff Parker: thanks for posting this thread. Your photos have really got my cogs turning. I've been threatening to do a laminate for a long time and you and Clay have convinced me that I don't have to wait for a vacuum bag system to try it.

Hi Jeffrey,

I laminate each side seperately. I want the traditional book matched look.

The carbon fiber is something new I am trying. I use regular carbide tipped sawblades and router bits. So far so good. Since you have some experience with this stuff, perhaps you can offer some insight on the best tooling and techniques for working it?

I fooled around with a vaccuum bag for a short while, but never really got tooled up for it. I believe Al Dodson has some experience laminating sides using vaccuum bags.

Thanks for the info, Clay. My experience with carbon fiber cloth is mostly with laying it up on the surfaces of foam forms without using a vacuum bag or male-female mold. For one-off fairings or "frames" for human-powered and solar vehicles, that lay-up process was best for me to develop a working prototype. A bit rough, at times, but I could cover it with a layer of fiberglass and epoxy resin if I wanted to finish off the surface slick. Sanding was no problem with any power sander and most of the grinding or cutting was done with abrasive discs - also an option to working with carbon fiber in relation to instrument construction, I suppose.

I use carbon fiber rods in some of my necks and recently, I had to plane a headstock face of a neck with two rods already installed. I thought I had plenty of room to go, but I just barely nicked one of the carbon rods... and I mean BARELY. I'd just changed my jointer blades a week before, so they were sharp and perfect. Now, there's one hooptydoo in the blade that keeps me from getting a perfect plane on a wider surface and I always have to scrape that raised line off the stock before I glue up a faceplate. Aargh. CF is murder on non-carbide tools. Glad to know the carbide ones are holding up.

I have access to a vacuum bag system at a friend's furniture shop, but I like the male-female mold idea, too. Jeff Parker's method with the caul blocks layed out on a canvas strip is pretty cool, as well. I'm sure a vacuum system would also require a caul at the waist and likely one on either end, so the only difference would really be in the clamping method, though vacuuming might be a little more consistent and more economic timewise.

I'm really interested in how laminating works out for everyone using it and look forward to hearing more about the results. I've been aching to carve a back mold and laminate a back with a vacuum bag, but Jeff's method with the go-bars and cauls isn't a bad idea, either.

Another, perhaps trivial, advantage of vacuum clamping is it's ability to suck excess glue or resin (and any air bubbles) out of a lamination thus keeping the weight to a minimum and minimizing chances for later de-lamination.

Jeff,

I'm curious as to whether the urea-formaldehyde glue you're using is activated by the addition of warm water or is it catalyzed by the presence of some other solvent? If it is the water-activated stuff, have you had any problems related to the water content - problems related to expansion and later shrinking?

We did quite a bit experimenting with vacuum forming of sides and backs; it was evident that we could quickly make far more sides then we could use. The vacuum ensures there are no voids and is not all that difficult. For the sides we use bags made from rolls of seal-a-meal bag material and formed them over an inside mold. There may be a discussion in the library (or headed that way) about our process.

The process works something like this; glue up the veneers and place them in the bag. the laminate is then placed over the mold and the vacuum pulled. Then it is pulled down at the waist and clamped. Next we clamped in a few more places around the mold. The really cool thing is that we could then seal both ends of the bag and shut down the vacuum pump freeing it up to go on to other sides or backs. I suspect you could do this with an inside mold too. These worked out great.

The backs we did over a mold and used a vacuum frame or table arrangement that we built. It's pretty straight forward and I think there are plenty of details at the Joe Woodworker site. The backs didn't come out as well but that could be fixed by changing glue.

We tried several types of glue. Yellow glue and epoxy bleed through without fail; not a good thing in my mind. We found a Tite-bond product made for veneering and that works real well, except for the water, which was a problem with the backs. The sides were not a problem; they could be taken from the bag after 12-24 hours and clamped back in a mold to dry and retain their shape. The backs being so large would retain a lot of water and would tend to flatten out when removed from the vacuum (these were sides for Selmer style guitars with a 1/2-3/4" dome). We didn't get around to trying the 2 part glues which,I think would solve the problem.

One more thing I explored was using 2 layers of the 2 ply veneers that are available. What I found is that these 2 plys are glued with some sort of Tyvek like fabric between them and who knows what type of glue. I don't think this is suitable for guitars so I gave up on that stuff. BTW we laminated 3 layers with the center running cross grain which made a very stiff side.

The urea glue I use is just mixed with water. You mix it relatively thick so it does not soak into the wood very much. The only problems I have had with the sides splitting is if you try and laminate them soon after bending. I try not to wet them too much to bend but even so I put them on a form and let them air dry for a week or two before laminating. I use a regular guitar side and laminate the two ply on the inside with the middle layer running perpendicular to the grain so inside and outside the grain runs the traditional way. With the all wood veneer I do not think there is any fabric between the layers. If there is it is not visible to the eye. On some of my backs when you take them off the mold the internal stress causes them to flatten on the long axis but as soon as you clamp it back to the sides the dome radius reappears. The amount of flattening appears to be related to the thinness of the back and the species of wood used. I think others have gotten around this by using a back mold which has a radius dish that starts about one inch in from the sides. That effectively creates an angle brace around the perimeter of the guitar. Jeff

Hi Jeff Parker,

Tonight I made some molds by thermoforming Corian. My laminating process requires curing the layup for a week in the molds, so it takes two weeks to make a side set using a single male/female mold. I decided I would like to have at least two molds so I can layup a pair of sides at one time. Rather than make another plywood mold I cut a strip of corian and laid my bending blanket on it. I let the corian become plastic then layed it over the male mold. I kept the blanket on top of it and laid a strip of kerf core on top of that. I clamped the corian/heat blanket/ kerf core sandwich to the male mold, turned off the blanket , then let things cool. The corian took the shape of the female part of the mold. To use it I will lay the waxpaper /veneer/ waxpaper sandwich inside the female mold , then clamp the kerf core against it.

It took so little time to do (about 20 minutes) that I made another mold just for fun.

Hi Jeffery Jones,

I have the veneer/CF cloth/veneer back and sides assembled. When you mentioned about your experience with the jointer of course I had to try it. The layer of cloth is very thin yet it nicks the blades every time! I had to do this three times just to be sure I wasn't imagining it. The CF does seem to work o.k. with carbide tooling (saw blades and router bits) and sawed quite easily by hand (coping saw). Normally my epoxy/ wood layups have a glassy tap tone. The wood /CF/wood epoxy layup has a tupperware tap tone. But i will take it to completion. Sometimes things work out better than they promise to.

The wood /CF/wood epoxy layup has a tupperware tap tone

Perhaps if we used Brazilian Carbon Fiber cloth?

I'm very interested in trying out something quite similar. Mebbe we can find the why behind the tupperware tone, and rectify such.

How thick is the overall plate? What thickness were the veneer? What is the veneer? What weave and thickness is the CF? What epoxy was used? Clamping methods and duration?

What temp (approximately) is needed to mold the corian?

How thick was the corian? Questions, questions.

At the rate we're tossing questions at him, Clay may never post here again

Hi Mario,

With the CF layer the veneer is much more flexable and I bent a piece of offcut (with the grain) back on to itself (to about 1/16 inch radius) without it breaking - much as tupperware would do. Brazilian rosewood tupperware dishes anyone?

Hi Steve,

Corian thermoforms at about 300 degrees. I lay the blanket on it and wait for it to slump. The corian must be heated all the way through. Forcing it too early will cause it to crack. I have the 2.5 watt/sq.in. blanket which seems to work fine.

Hi Barry,

The corian was the standard 1/2 inch thickness stuff. It might be another way to mold a fingerboard clamping caul.

I have been thinking this might also be a quick and dirty way to make the forms for holding the sides during construction. With a tab glued on either end they could be clamped or bolted together.

Thanks!

I suspect part of the tupperware tone is because the final thickness is so thin. But I also suspect it will be fine once braced and built...

You wouldn't know the weight of the cloth, would you? I'm surprised that it didn't add any thickness and that the whole laminated plate was thinner cured than it measured dry...

Hi Mario,

The cloth was somewhere in the 4-6 ounce range. It was an "end of roll special". I too was surprised it measured thinner after than before, but after working with the CF I can understand it. A stray strand of it was laminated to the outside of the plate and to remove it I scraped it off with a razor blade. I expected it would leave a depression as a strand of fibreglas would leave, but instead it was like scraping off a heavy pencil mark. The stuff compresses to nothing! It is tough on jointer knives though, and after jointing leaves little fuzzies sticking out of the joint. I knocked them down with 60 micron paper before gluing the joint together.

I still have a little bit of cloth left and I may try it again with thicker veneer. I do think it adds some toughness and the sides would have "tapes" built in.

Interesting... Anyone know how many layers of 6oz CF cloth is needed to get a .025" solid CF laminate?

Cf weighs about.00617 oz per cc. There are about 1800 sq inches in a cloth yard (36x50). Doing it in my head I come up with about 28 layers. I could be wrong.

I think Clay meant 0.0617 oz/cc, since the specific gravity of CF fiber is about 1.8. The specific gravity of a laminate of bi-axial CF fabric in an epoxy matrix is about 1.5 - 1.6.

I didn't follow Clay's math , but I did a quick check in Vectorlam software. Vectorlam predicts that 14 layers of 6 oz carbon fabric in epoxy with a fiber content of 62.5% would have a thickness of 0.125". That is consistent with Clay's result. (Vectorlam only has enough fields for 20 layers, so I went for half of the thickness).

For comparison, I recently laid up some unidirectional prepreg material which was four layers of 600 gsm carbon. Vaccum bagged and cured the plate thickness was about 0.1". So roughly, I would have needed 10 layers of 600 gsm to get up to .25", which would be 6000 gsm. Since 1 oz/sqyd = 33.894 gsm, that means I would need 177 oz/sqyd of fabric, or about 29 layers of 6 oz fabric. Roughly.

0.025" is what we'd be after, not 1/4" So, following the math that gives us 14 layers = 0.125", 3 layers would be as tad over 0.025". Cool?

Yup, 3 layers sounds about right.

(I coulda swore that said 0.25" :) )

O.K. 2.8 layers - a slip of the decimal point. I shouldn't try to do this stuff in my head.

Here are a couple of types of forms I use for molding sides .

The one above is a simple block board male/female form that is lined with laminate to make a smooth surface. To perfect the form the laminate is "glued" with bondo and pressed together with a flexable material which is about the same thickness as the laminated side will be. This allows the form to press the veneer together more evenly.

The second form is thermoformed corian and kerf core. The corian provides a rigid shape and the kerf core conforms to it. In both types of forms I use wax paper between the lamination and forms.

Here is a picture of the corian form in use.

Interesting!!

In post 39 you will notice that I made two "left" sides. I hate it when that happens!. Luckily I have enough rosewood left from that flitch to make two matching right sides.