Saturday, July 17, 2010

Adhesives


I’ve been asked a couple of times whether or not I use hot hide glue on my instruments and the simple answer is, no.

When I was at college, Herbie (tutor) tried to get all of his students to use hot hide glue and there are sound reasons for using it, but I simply do not like the idea of subjecting my wood to unnecessary heat and moisture when there are excellent alternatives available. One of the arguments for using hot hide glue is that you can take the joint apart easy; great if you are repairing 200 year old violins, but do I want to take my guitars apart? Do I want my guitars to come apart!

I mainly use Titebond Original, this glue has been used by most luthiers and manufactures for decades and its performance is proven. My early guitars were put together with it and after 30+ years the glue joints haven’t failed. Apart from its strength, it dries very crisp and therefore, I feel, won’t dampen vibrations. I’ve also been using Titebond dark occasionally; the main thing about this version of Titebond is that it’s waterproof. I’ve used it to glue purfling lines to bindings before bending them; they can then be soaked prior to bending. It can, however, make glue lines visible on lighter woods (even mahogany) and doesn’t dry as crisp as “Original”. I also use Titebond hide glue for temporary joints, like you saw in my wooden rosette post. Hide glue for temporary joints...see what I mean!

I use epoxy resins for gluing dissimilar materials i.e. carbon fibre to wood. Slow setting Araldite is my favourite; I find that the Rapid version never really goes completely hard and therefore I tend not to use it. I’ll use Araldite when I’m gluing components together that will be subjected to some kind of stress. If I want a fast setting epoxy, I like to use Z-poxy; this is good for inlays.

I also use epoxy where I have to glue to end-grain (the neck block in cutaway guitars is a good example). As all woodworkers know, you shouldn’t glue onto end-grain, this is because the glue is taken away from the joint by the exposed tracheids in the end grain. Epoxy uses these features of the grain as a key to increase grip.

Cyanoacrylate or super glue is also extremely useful. I think that most luthiers tend to use it now for securing frets. Some CAs are so thin that you can place little drop on the end of a fret and capillary action will pull it along the whole length. This phenomenon also makes it useful for repair work when gluing cracks together. On some burr veneers which naturally have small holes, I coat the veneer’s surface with CA and sand whilst the adhesive is still wet, thus any holes are filled with matching dust. Take care- if you use lot there can be an exothermic reaction and you can burn yourself. Oh and be careful not to glue yourself to the guitar, it’s just plain embarrassing!

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