One of the questions I often get is how a guitar or lute top is joined using traditional methods. So with hot hide or bone glue.
Well, today fellow guitar maker Joës van Went was at my shop and took some time to film the process.
I learned this technique from Belgian luthier Stijn Kenens, who picked it up at the CMB lutherie school in Puurs. It’s an old method, used by many traditional Spanish makers.
I prefer this method because it’s relatively low tech and doesn’t involve a lot of tooling. Some rope, sticks and wedges, a little cotton tip torch (I fill mine with some old Courvoisier cognac for a better, warmer tone) and hide or bone glue. The purpose of re-heating the glue to make it more liquid and allow the glue joint to be pulled tight. You can also use Titebond, then there is no need for warming up the glue joint.
The Dutch Luthier 
What is the purpose of the fire?
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The hot hide(bone) glue inevitably cools over the course of laying on the ropes and cauls. The purpose of the fire is to warm up the glue joint again, for better adhesion. Notice that he tightens the wedge-shaped cauls once more after he’s heated the joint.
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heats the hide or bone glue back up to make it more liquid and to create a tighter fitting joint
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Re-heating the glue to make it liquid again and flow between the joint while pulling it tight.
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I see, thanks for the explanation.
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I trust those cauls are waxed–and maybe the ropes too, just in case…
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No need, there is a little slot in the caul at the height of the seam. In order to allow the flame to get through and prevent sticking. Besides that it is very little glue, so to get the wedges permanently stuck would be rare.
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I just clamp down a couple beams on a flat table, set to where top sides form a roof shape (about 1/2″ at center on an average classical/dred size), spray a bit of mold release spray on surface to keep glue from sticking, add glue to seam, push down, tap will a mallet to even out any seam issues, and throw a movie grip sand bag on it. Comes out great every time! Gravity does it’s thing…
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