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Edward Powell
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i see... so you used veneer because the original used veneer?
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jdowning
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Yes
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jdowning
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The first (unsuccessful) attempt at making the sides of the guitar from veneer was to make a 2 ply construction - two veneers glued together with PVA
glue (Lee Valley 2002 GF - high solids content and high viscosity to minimise chance of glue seeping through the veneer causing surface glue stain).
The grain of both veneers was longitudinal.
After gluing the veneers were clamped between two flat boards to dry.
On release from the clamps - on further curing - the blanks became warped ('cupped') across the grain. This is likely because knife rotary cut veneer
was used rather than quarter sawn.
The sides were then bent over a hot iron in the usual way. It was found that bending dry without dampening the surface with water caused 'blistering'
- local separation of the laminates. This was avoided (and repaired) by first moistening the surface of the blank before hot bending with the bending
iron held below scorching temperature.
However the bending process was still not completely successful as it was not possible to maintain flatness of the ribs across their width so this
trial was abandoned.
I still have the test samples so can post the attached images. The total thickness - including the glue line - is about 1.05 mm equivalent in
thickness to that of the original guitar (see the attached macro image)
In retrospect I figure that the hot bending would have succeeded had I made the blanks as a three ply construction with a thin cross grain core -
which is what I did for the next stage to follow.
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jdowning
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For the second (successful) attempt at making the guitar sides or ribs from veneer laminate, a three ply laminate was constructed using a caul or
mold. The laminate was a 'sandwich' of two outside veneers of Brazilian rosewood (both with grain direction longitudinal) with a thin cross grain core
of mahogany veneer. The core thickness was about 0.25 mm (they make modern veneer very thin these days!) - giving an overall finished rib thickness of
about 1.3 mm.
The caul was made from layers of plywood glued together to a thickness of 3.5 inches (about 9 cm) and then accurately cut to the outer half profile of
the guitar using a bandsaw to ensure vertical sides to the caul. Clamping blocks matching the inside profile were cut and then lined with foamed back
carpet to provide a resilient surface over the laminate under clamping pressure.
I still have the original caul but cannot now find all of the clamping blocks. No doubt they will surface some time in the future (see attached
image). The blocks were clamped to the caul using large 'G' clamps.
The depth of the caul was made oversize to allow trimming of the side blanks.
The sides of the caul were wax polished to avoid any risk of the veneer sticking to the sides should there be any glue 'leakage' through the
veneer.
I cannot now remember exactly how I glued up the laminates but seem to recall that it was done in two stages - inner core to external veneer then -
after the glue had dried - inner veneer glued in place.
The glue used was Lee Valley 2002 GF PVA and the laminates were glued 'cold' without need for application of heat. As the glue has an open time
(before beginning to harden) of about 15 minutes there was ample time to align the veneers in the caul and clamp the blocks in place.
This custom made plywood is very stable and held its shape without any 'spring back' when released from the caul after allowing a few days for the
glue to thoroughly dry.
Next to the veneering of the back of the guitar - a two ply construction like the original.
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antekboodzik
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May I refresh this topic? Just in case that this topic turned out to guitars 
Many modern classical guitars have solid backs and laminated sides (e.g. macasssar ebony for back and macasssar/ash sides). What is the difference in
sound, or maybe to another material/techniques to be used, versus solid sides?
I was often thinking that laminated sides of contemporary guitars helps to create stronger "drum" like effect to the soundboard as a membrane.
Laminated sides could then be made thicker (and thus much stiffer), as then solid sides of more than 2-2,5 mm would be extremely hard to bent.
Can laminating sides of veeners be considered as an (cheap, relative easy) option to make a guitar (for flamenco music (!?) ) by amateur like me?
Veeners of different wood about 0,7-0,8 mm are widely available and cost a fraction of price of bookmatched professional sets. Do this technique apply
to making backs of guitars?
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Edward Powell
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Sides of guitars don't make much influence on the sound.
I would not recommend building with any plywood, like making your own with veneers - mostly because thin veneer is always a problem because if for
some reason you need to sand more than half a mm. very likely if you are beginner, then you will sand all the way THRU one veneer and BINGO you have a
big problem.
If you want to same money then just use a more common wood like maple... that's very cheap... or beech, ask, or even make the whole guitar from
spruce - why not?
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antekboodzik
Oud Junkie
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Well, here in Pomerania there is extremely hard to find even a single maple
Yes, this is a point with sanding, or scraping, thin veeners. But I can use same wood for both layers, even bookmatched pairs of dark in color timbre
Another consideration is about glueing along center line rather thin (not more than 2,5mm total), laminated back panels... Executing this precisely
might be a challenge, if even possible.
Guitar made of beech? It would look like a piece furniture Ash wood maybe a
graet option, but again, I can get easily only veeners up to 2mm and planks of more than 4,5mm.
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jdowning
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For some reason I gave up on this thread way back in 2012. I had intended to continue with information on veneering the back of the Grobert guitar
copy.
According to the museum notes on the original instrument the back is a laminate of a softwood (spruce?) and Brazilian rosewood veneer. This is not a
good combination as plywood is stable only if odd numbers of laminate are used. This is not a problem when veneering furniture, boxes etc where any
stresses induced by the application of the thin veneer (glue shrinkage) will have no effect on the substantial underlay. Less so for the relatively
thin back of this guitar.
The method that I used 18years ago when making the instrument was to support the spruce back on a plywood board prior to veneering (with hot hide glue
in the traditional way). The method used was reported in more detail in the attached FoMRHI article.
An alternative to hot hide glue would be synthetic PVA carpenter's glue. Both surfaces being coated with glue, allowed to dry and then ironed together
with heat from a hot iron. Another modern method would be to use a contact adhesive - no heat or glue shrinkage to deal with.
Note that veneer has a smooth surface so little sanding is required for finishing. An oud bowl made from laminated ribs would , however, have to be
made with 'flat' ribs (like a lute) and could not be sanded into a smooth outer surface as noted by Edward due to the thinnness of the veneer.
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antekboodzik
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Great article, thank you a lot.
Well, so summarizing (correct me if I am wrong):
- what many people say about tonewoods, and some aspects of construction, velocity of sound in materials, is a BS
- selection of wood for back and sides of guitars and lute ribs has minor influence to the sound (regarding apropriate construction methods),
- more important is general overall of construction, e.g. differences between flamenco and classical guitar, than the particular wood selection,
- in past years solid backs and sides for guitars (citterns, opharions) were simply easier to execute, but some top makers invested time in cutting
own veeners and laminating them for tonal qualities,
- nowadays, with powertools, "veeners" are much more available to buy or make, and laminated guitars can be equal in tone quality than guitars made
traditional way, however making laminated parts is quite sophisticated work,
- lute ribs would present certain difficulties to be made laminated, but it is not impossible.
Another issue is, that I tried several times to "laminate" two pieces of 1,5mm maple veener, by applying some hot hide glue and putting some weight on
it until dried. But no matter which orientation of grains, it ended in less or more saddle like shape...
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jdowning
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Instrument acoustics is not a generally well understood science - there are so many variables involved - so there is some (but not all) unfounded
opinion about this and that concerning instrument construction and material selection.
Velocity of sound in instrument woods is one viable quantitative measure that may be used to judge the acoustic property of wood as an aide to
'tonewood' selection.
The flat back of a conventional 'classical' acoustic guitar does contribute to acoustic performance as it acts as a secondary soundboard. So wood
selection and construction of the back, in this case, might be expected to be of some significance acoustically? On the other hand a heavily braced
thick back would be less responsive in this respect.
Mass produced instruments of the violin and guitar family have been made from plywood for years. They are relatively low cost instruments and - as far
as I know - of relatively low acoustic performance. This does not, of course, mean that a hand made instrument made from wood laminates by an
experienced luthier would not perform well.
As mentioned earlier in this thread, a stable laminate (one that will remain flat and not tend to curl up) should be made from three laminations (or a
greater odd number) the grain direction of the central 'core' being at right angles to the grain direction of the outer laminates.
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antekboodzik
Oud Junkie
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Mass produced guitars, even with acceptable quality (at least to my eyes) of solid top have often very crudely executed bracings (not well shaped
several bars at right angles to the bridge), and, what is horrible, a bridge supported by two screws... I would once take a risk and replace a top on
a badger guitar to see if there would be an improvement.
There is a legible tendency to make sides and backs of CG very heavy (often up to 1cm!). And Smallman's guitars - with frames, lattice bracing
reinforced with carbon fibre, and laminated tops - do they are guitars (or wooden drums with strings)?
If good, concert quality instrument can be made with quite big variety of woods for back and sides, and also with combination of spruce and cedar
tops, AND, what more, using lamiantions or not, do it really matters? See that there are inconsistient oppinions which wood works better with spruce
top or a cedar one (on guitars).
Also, I think that classical/flamenco guitars (and somewhat ouds too) are evolving nowadays like no other instruments at all. It would probably never
happen to the bowed instruments. I wonder, if ancient oud and lute makres could play today's instruments, they would say "hey, that's exactly what I
was looking for all my luthiere carrer"
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narciso
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I have experimented quite a lot with plywood for soundboards on various instruments, since getting hold of spruce properly quarter-sawn and toned
seems to be the principal cost factor in any project
The omnipresent cheap 3mm poplar laminates actually give a surprisingly resonant soundboard in my experience, although a bit cardboard-y ... as one
expects.
It is fine to use no bracing at all with plywood, the conventional wisdom being I suppose that the function of the bracing is to stabilize against
cracks along the grain and to distribute the sound perpendicularly. Both these roles are inherent to the cross-grained laminate structure of typical
plywoods
(somebody has probably pointed this out already somewhere or other in this thread)
As a curiosity, just for fun I have also found it possible to make a viable 1mm thick lute bowl using birch strips steam-separated from old birch
plywood
A bit pointless admittedly, as good quality veneers are cheap and straightforward to obtain
At the time, I was teaching in a Venezuelan outback far from any hardware store !
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