Sunday, 10 November 2019

Building a 13 Course Lute, Start to Finish, 7: Bracing the Belly

Hello again. Today, another adventure in lute making: shaping and gluing the braces on the backside of the belly. Perhaps not the most glamorous job in the lute maker's resume, but essential to the sound and structure, and eventually the action, of the finished lute.

At the beginning of this blog series, somebody on social media asked me a question something like this: is building a 13 course lute all that different from building a renaissance lute? My answer could only be superficial, but I said yes--and that's mainly down to the fact that whereas a renaissance lute has a relatively flat (though not completely flat) fingerboard, a 13 course lute has one with a very pronounced arch. Practically every operation bends--often, quite literally--toward accommodating that feature. Today, we'll really start to see that principle in action.

[Small editorial comment here: throughout this post I will refer to 'braces' and 'bracing,' rather than 'bars' and 'barring.' I think the former is more a British usage, the latter more commonly a North American one. Writing in Canada, and in Canadian as I do, I'm generally more likely to go with British spellings, though in this case the Britishism seems a bit foreign to me. However, I've decided to use it to alleviate confusion when I start talking about go-bars and the go-bar deck.]

In my last post, I carved the rose. Upon finishing that job, I hung up the belly one more time in the light box for 24 hours, in a low-humidity environment, for another round of humidity cycling (described in more detail here, in the 5th instalment of this series.) After bracing the belly I won't be doing any more humidity cycling, since the braces are glued across the grain (and to put the assembly in a low-humidity environment at this point would be disastrous.)

So no more humidity cycling with the belly, but I will nevertheless continue to carefully control the relative humidity in my workshop, in two ways: by using a small oil-filled heater to warm my work room, and, when the relative humidity is a little too high for that to handle, by turning on my dehumidifier. These two little appliances can make working conditions uncomfortably warm at times, but together they enable me to keep the r.h. in my shop in the low-40% range, which is optimal for crucial jobs like gluing on braces, and, a little further along, gluing the bridge.

Here's my brace material: alpine spruce, from the same source as my soundboards. It's sold in split billets, which guarantees that the pieces I cut will be practically free of runout. (Watch out for that knot!)

After cutting braces to generous length and height, I take them to a quite exact and uniform thickness with a bench plane.
I have a planing box for the purpose--just a small plank with some edging--which fits into my bench vice.

All three sets of braces are 'roughed in' for all three lutes. The brace dimensions and locations are based on historical examples, and on my own years of experience building a lot of lutes with the same or very similar material throughout. (One does get to know one's material quite intimately after a while.)

I bend thicknessed sheets of material for j-braces using the bending iron and a bit of water from the spritzer. Later, when they are cooled and dry, I will cut individual j-braces from them in the bandsaw.
Once the braces are prepared, I'm ready to go ahead with gluing them on the belly--and I will complete all the work to follow in today's post in about 3 hours. It's essential for me to do all this work at one go, to ensure the freshest gluing surfaces and the most consistent shop humidity. These precautions--these principles--will do much to ensure the finished instrument is as durable and as sound as it can possibly be.

I scrape the belly. Not to remove much material, only to refresh the surface of the wood by removing the slightly grimy, gluey and oxidized outer layer. 

I mark the centreline, and the positions of all my braces.

I locate the body of the lute very carefully on the backside of the belly, and trace the outline. I use wedges to lift up the middle of the belly (remember the belly scoop from episode 2?

I then shoot the bottom of each brace, to give a fresh, perpendicular gluing surface--and, on quite a few of them, to create a carefully controlled amount of curvature on the underside of the brace.

Take, for instance, brace #7--the highest on the belly, the one closest to the body-neck joint and therefore to the fingerboard. The fingerboard, at the body-neck joint, will be significantly arched--somewhere around 3-3.5mm across approximately 100mm of width. That fingerboard arch cannot simply stop at a dead-end where it joins up with the belly; there must be some sort of transition between the fingerboard curve and the (relatively) flat surface of the belly. To achieve this, I plane curves into the top three braces, gradually easing the amount as the braces approach the rose.

This is the way I will support the belly to glue on this curved brace: with carefully-shaped curved cauls. The cauls are made of strips of cardstock, cut to length, stacked, and taped together.

As you see here, it's not only the top three braces that are curved--there is also a small amount of curve in the first two braces in front of the bridge. (I'll explain the reason for the curves in those braces when the time comes, in a future post.) I also place a thickness of cardstock under the rose, to support it, and a few small wedges of card to support the uncurved braces below the bridge.

What can I say? The three-dimesional geometry of a 13 course lute belly is very complex indeed. Stick with me; all will become clear. 

I locate the belly very precisely on top of these curved cauls, on the bottom floor of the go-bar deck. Almost ready to begin gluing... but first, back to the braces for a minute or two.

A little more shaping to do: I use my trusty low-angle block plane (with a very sharp, and slightly curved, blade) to slightly taper the braces, so they are narrower at the top. A few strokes with the plane on each side of the brace is enough, and I am careful not to reduce the already-established nominal thickness of the brace at the bottom.

This is the kind of profile I'm looking for.

Here's how I shoot the bottom of the j-brace: by running it over the upturned bench plane in the vice.

Almost ready to glue, but first I ink black the bottom surface of the three bars that cross the rose (note the authentic 16th century Sharpie.) There are three bars across the rose, and I black only the portion of the bottom surface that crosses it. 
Here's the best shot I have of the whole go-bar deck and glue pot rig. I'm reaching up on the top of the deck, where the oak go-bars are kept (and, may I say, also rocking quite a saucy pose.) I'll be reaching overhead for go-bars throughout the gluing process.
Here's how I glue. Starting at the bottom of the belly, I take a bar, hold it above the rim of the glue jar and brush glue upward onto the bottom surface. I keep dipping the brush in the jar, then brushing hot glue upward, ever higher, until I've got good, even coverage with glue that is a pretty uniform temperature.
And then, I get the bar down quickly in place on the belly, giving it a slight rub as I do so, to ensure good initial contact. Holding the brace in spot with the palm of the left hand, I reach up with the right to grab a go-bar. Still holding the brace securely with the lefthand palm, I use the left fingertips to locate the tip of the go-bar on the top of the brace, while the right hand swings the upper end of the go-bar into place directly above, against the ceiling of the go-bar deck.


Yeah. I just read that over again, and it might seem a bit confusing. But really, that's how it goes, and short of actually doing a video of me working (which I'm not interested in doing), I can't make it much clearer. You'll have to just take my word for it--or, better yet, try it yourself.

Still holding the brace with the left, I place two, three, four, or even five more go-bars, as needed, in order to secure the brace. Then onto the next.

Here's the first brace. Seems like a good start.

Oh yes, and after I glue each brace, I clear away excess glue with a long-handled brush whose ferrule I've bent for the purpose.
About half-done. It's getting to be quite a forest of go-bars, and I must be careful as I glue each successive brace not to nudge the go-bars of previous braces. (A domino-style disaster is thus averted.)

Full shot of the go-bar deck. This one was made by and belongs to Grant Tomlinson, whose shop is right next door to mine, and who kindly lends me it whenever I need. (I have my own set of go-bars which I use with the deck, however.) 

We see the top bar here, the one with the most curve, with the belly beneath supported by the curved cauls.

One more shot of the go-bar deck? Why not. It's a simple piece of machinery, but it works perfectly. I love that kind of technology.

And next morning, after carefully taking down each go-bar, and removing the belly from the deck, I see my result. All the braces are securely glued, and they look reasonably orderly.

However, most of these braces, I will confess, are not placed with an excess of precision. I get them in basically the right spot, but, as you can see, there is some randomness to the angles of most of them (the top two, especially, seem a little askew--or is it the third one?) But that's actually what I'm looking for, a little randomness. One sees it all the time looking at old lute bellies. As with their rose carving, one gets the sense that the old makers actually distrusted too much symmetry, proportion and control, and actively as a principle courted a certain amount of chance and randomness in their work. Perfection is a kind of death, both visually and sonically; imperfection is energy and life.

 Next time: shaping the braces, and fitting up to the body. Have a wonderful week.

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