Recently, though, I have begun the process of gluing on and shaping the braces for the instrument. The instructions are somewhat incomplete in this regard. As I noted elsewhere, the instructions don’t really have any kind of direction on when to shape the ends of the braces during the glue-up process. It turns out to be practically unambiguous because you have to shape the ends of the short braces on the top before notching and gluing on the trans braces on the top. If you look carefully at the photos for the surrounding steps you can even see it has been done in the photos (although the photos for the nothing and gluing of the trans braces show the short braces carved in one photo and not yet carved in another, so that you can’t even get useful information indirectly on this point). But the instructions don’t tell you to do it at this time, and crucially they don’t tell you how to do it, either. You get some instruction on this point in a later step (there are two places where you have to shape braces), including a photo (the photo I included with my last post), but this is a logic bust in an otherwise very well constructed set of instructions and drawings.
What I really found disappointing is that I can’t find any instructions anywhere in the plans on when, or again crucially, how, to carve the braces. To make this deficiency clear it will pay for us to look at a photo of the plans.
This is the plan cross section of the short braces. See how the braces are supposed to be carved in a sort of boat hull shape rather than left rectangular in section the way they are delivered? (For my purposes I will use the word shape when talking about shaping the ends of the braces and the word carve for carving the sectional shape into the braces.) The plans don’t tell you when to do this carving. Now, it might seem that it doesn’t much matter when you do it, as long as it gets done before you glue on the top. It might even seem not to matter if you do it, although clearly not carving the braces has the effect of leaving an inelegant feature of the instrument and more critically of negatively affecting the response of the instrument while playing. (I read this in Guitarmaking, the Bible on the subject. I don’t know this from experience, but as a structural engineer – at least by training – it is obvious that this would be the case. Leaving the braces uncarved would substantially increase the stiffness of the top, thereby reducing its response to the vibration of the strings. Usually considered a good thing in highway bridges, but it would be a bad thing in a mandolin.)
Back to topic, the problem is that there is definitely an optimum time to carve the braces into this shape. You can’t carve them before gluing them to the top because then you’d be trying to clamp a pointy surface and the clamp would have trouble gripping the brace, and the extra material makes the brace stiffer so that you get more uniform clamping pressure with the limited number of clamps that can be brought to the party. So carving them on a bench away from the top is out. You therefore have to glue them on and then carve them. But that’s where it gets hazy for me. What do professionals do about carving the braces?
Let me take a moment to explain that carving the braces is tough. You can see in my photo that this was the hardest part of the process for me so far, and in fact I didn’t do it all that well. I’m satisfied enough to glue the instrument together – after all, except for the readers of this blog nobody but me will ever see the braces once they are inside the instrument – but obviously a professional builder would probably resort to using the top as firewood rather than sell the instrument with these braces on it. I suspect that the professionals use little planes in this process to take very thin, regular shavings of material, for at least part of the time they are carving braces. I don’t have any way of knowing this, though, because the plans did not include a single word of instruction on how to carve the braces. In fact, other than the little section on the plans and the fact that some of the photos – but not nearly all of them – show the braces carved into the desired final shape, carving the braces is simply omitted from the instructions entirely. So I used a chisel to carve them – the same one I used to shape the ends – and it came out better on some of the braces than it did on others. I think the short top braces look OK, but the trans braces look much less so. If you were to look carefully at the top of my instrument you would also see several places where I gouged the top ever so slightly while carving the braces. Unfortunately the cardboard mask I was using to protect the top while shaping the braces was too thick to permit its use during the entire carving procedure. I sanded these areas smooth.
Again back to our topic – when and how to carve the braces. I addressed the difficulties in carving the braces above, and also the method I use as well as the method I suspect the pros use. But the timing thing is another problem. You see, I glued on all four top braces before carving any of them. I’m betting that a professional would have glued on the two short braces, shaped and carved them, and then glued on the two trans braces. That way you would minimize the interference of other braces when carving the one you are working on. Sadly this did not occur to me until I was essentially locked (glued, you might say) into doing it my way. Because of this a small plane of the type I hypothesized about might not have been much help to me – the other braces would have interfered with the sole of the plane and prevented long cuts to the ends of the braces. Maybe pros don’t use planes for this very reason. At any rate, I carved the two short braces after taking the long braces out of the clamps, and then shaped and carved the trans braces. I wish I had done a better job but I guess you have to do it a number of times before you’re going to be great at it. The job I did will suffice for my first instrument, and I’m sure I will do things a bit differently on the next one.
Here’s a photo after the carving and shaping step (the other short brace looks much like this, the trans braces don't look as good):
Memo to Stewart MacDonald: please add some clarification of the carving process, and please do it in the appropriate place in the process. And thanks for the otherwise great kit!
No comments:
Post a Comment