End grain glueing advice

[Kalimna]

Greetings folks,
Having acquired over christmas another book on guitar building, I've decided to make an effort and get started with my long-gestating guitar build. Most of it I think I can work through (and it will be an excellent oppurtunity to use the radius blocks I received from Phillly last year ), but for the body I have a particular idea I want to do.
It essentially involves glueing several boards of varying thickness at varying angles across the (electric) guitars' body. The two woods will be padauk (main bit) and sycamore (contrasting stripes). There will be varying degrees of end-grain to not-end-grain gluing, and I would like to know what people would consider to be the best glue for this? Cascamite? Epoxy? Titebond? PU? I dont think there is any other way I would be able to achieve the effect I am looking for (EVH's original 'Frankenstein' guitar in wood, not tape), however.
So, I look forward to any help the collective can offer

Cheers,
Adam

 

[Jacob]

I built a lute about 30 years ago and stuck it all together with ordinary PVA wood glue. No problem. It's still together. You hear lots of suggestions of problems such as 'glue creep' etc but nothing has happened yet!

 

[richarnold]

I once had to restore a cello, and part of the work included removing the neck. The instrument dated from 1802, and retained it's original neck. Most cello necks are fitted into a shallow mortice, but this one had been glued directly to the face of the ribs. It took me forever to get it apart, and it made me realise what a super strong bond you get with animal glue. Over 200 years of string tension trying to pull it apart, and it hadn't shown any sign of movement!!!

 

[Steve Maskery]

The two answers above do not, as far as I can tell, address the issues of end-grain-to-end-grain adherence. Unless I am missing something, which is quite possible.

I'm no expert on musical instruments at all, but generally, in situations where you have end-grain-to-end-grain joints, there is little direct strength. The integrity of the joint relies on the face-grain joints that overlap it, brickwork fashion.

S

 

[Rob Platt]

Biscuits
all the best
rob

 

[MIGNAL]

End grain to end grain will always be a compromised joint. Having said that try the old Fiddle makers trick with hot Hide Glue. That is to size the end grain. It involves coating the end grain in fairly dilute glue, allowing it to dry before repeating the exercise. Light sanding between. After 3, perhaps 4 applications the end grain will be thoroughly sized and you should see a visible sheen to the surface of the end grain. Then is the time to glue the joint proper. The strength of the joint is much improved when using this method. The only downside is that the glue sizing has a tendency to swell the grain, meaning the original joint may not be good. You can correct this at each sanding stage.
Try this on a few off cuts first. Then take your hammer to them. You should be able to get a feel for how well they are glued.

 

[Kalimna]

Thanks for your replies so far.
I had thought of using biscuits, but I only have a cheapo-BnQ-own-brand machine that is less than accurate in it's ability to hold an angle. Although that might not be too much of an issue if the remainder of the joint was spot-on. Obviously, the placement of the biscuits would need to be carefully done so as to avoid any body carving or hole routing.
Steve - there shouldnt be any direct end-end grain gluing, more of end-grain to face-grain at angles other than 90 deg (so the effect of the end grain should be lessened slightly). And being part of the body, there shouldnt be too much structural stresses involved once it is glued up.
Jacob - I have no problems using white PVA (though following advice from luthiery books and forums, I have used Titebond I), so if you think a PVA-type glue is OK for the type of joint I am planning, so be it.
Rich - Am I right in thinking that the repair you discussed was indeed an end-grain to face-grain joint? If so, then your experience tallies with Mignal in that hide glue is the way to go.
Mignal - Unfortunately I have no experience whatsoever with hide glue (other than the smell whilst on a course a couple of years ago), but the technique makes sense. I assume that using a PVA-type wouldnt work too well as a repeated 'size' as it doesnt bond to itself well? Do you think PU or cascamite would work well in that situation?

I appreciate the help folks

Adam

 

[Steve Maskery]

Well if you are talking an end-grain to face-grain joint, then that is a classic mortice and tenon, is it not?
S

 

[Kalimna]

Yes, but in a classic MT joint (which this isnt anyway), surely the strength of the joint lies in the side/cheek joint of face-grain to face-grain, and not the end-grain bit?

Adam

 

[Steve Maskery]

That is exactly my point!
End-grain-to-end-grain doesn't really work, whereas end-grain-to-face-grain does, by way of a hidden tenon.
I can't help but feel I am missing something here! Please don't tell me I'm being an ***** in public (again).
S

 

[deserter]

Loose tongues would seam to be the best solution here, in my opinion.


~Nil carborundum illegitemi~

 

[Kalimna]

I dont *think* you're being an ***** in public, but I also dont think I'm getting across exactly the joint I am trying to accomplish
I dont have access right now to a drawing package to simplify the explanation, but unless I include biscuits (or other floating-tenon style thing), there will only be end-grain to face grain gluing surfaces. And it will be the surface area of the glued up bits that should make this work, that and the lack of any particular torsional/shear stresses.

Think a block of padouk about 30"x20"x2" cut across the large flat face in several directions (one cut at a time followed by gluing up again) with the cut perpendicular to the large flat face. Next I want to glue in several 2" wide pieces (each of varying thicknesses) of contrasting wood (sycamore) in the space where the cut in the body blank was made. Each piece of sycamore will have to be glued in one at a time otherwise squaring up the end-grain surfaces will be a nightmare, and the clamping will be somewhat 'slippery' as there will be no squared clamping areas.
Here is a link to a picture of the guitar I am trying to emulate, though not nearly as 'complex' a design with the stripes, which will hopefully give you an idea of what I am trying to accomplish....

I have worked out the essentials of the process already of producing the body blank, it is merely the best choice of glue I am unsure of - and unfortunately I have neither the time nor the spare padouk to do trial runs

Cheers,
Adam

p.s Deserter - how would you suggest I produce these loose tongues, as it's something else I am unfamilliar with, unfortunately ? Thanks

 

[mrpercysnodgrass]

If I have got it right, I think there are two solutions to your dilemma. Have you thought about having one solid piece for the back ( a bit like constructing a semi hollow body ) and then gluing all your strips onto this back, this would mean that all of your pieces will be glued down with long grain, the front of the guitar will have the 'hatched' effect while the back can be left plain or painted/laquered in some way to match the front.
If you don't like that idea then I think your best bet will be to use west system epoxy, I can guarantee it will not come apart if you do. I use scotch glue for 90% of my work and although it has it's limitations, I think there is no better glue around. One of scotch glue limitations is in glueing end grain and it is for this that I reach for the west system, I have glued up countless legs and spindles over the past fifteen years I have been using it that have snapped across the grain and at the junction of joints and not one has failed. My only concern is your use of padauk, it is a very oily timber so I think you will have to scrub the joints with acetone before gluing, personally I would use a non oily dark timber for the contrast.

 

[deserter]

Make you cuts and run them over a router table or spindle moulder with a slot cutting bit (obviously on the sides to be glued) do the same with your end grain pieces. Then apply glue to the groove and insert a piece if suitably thicknesses timber, I normally use ply or MDF to be accurate as they come in the same thickness as a slot cutter, finally glue into the end grain groove and slot it into place, apply clamps as normal. Basically makes every joint into a mortice and tennon type of gluing arrangement.


~Nil carborundum illegitemi~