Monday, 12 August 2019

Building a 13 Course Lute, Start to Finish (2)

Hello dear friends, here's the second installment of the ongoing series, in which I chronicle the building of a 13 course lute. As I explained at the outset, what I want to do with the series is to document the stages of construction in as much detail as reasonably possible. I'm presenting photos of each discrete task, and accompanying them with a one- or two-sentence explanation of the operation depicted.

This is not, strictly speaking, a how-to blog, though of course I do hope (and in fact I'm quite sure) that much can be gleaned from my depiction of the process. Sometimes an image of a maker doing some operation, or a photo of a particular jig or setup, will be enough to spark the imagination of an onlooker who can take that concept and make it work for them in their own building practice.

However, I think that this post especially, in which I describe working with the bowl and doing the initial alignment of the neck, may prompt a lot of questions. That's natural, because my work in this stage will really lay the foundations for the instrument's final action and playability. If I work well and carefully now, I'll eventually end up with an instrument that has a very comfortable neck size and shape, a well-curved fingerboard, and string heights that are nice and low--all of which go together to create a consummately playable instrument.

I may, therefore, pause once or twice in the chronicle to give a bit of background and explanation of what I'm up to. I don't want to purposely confuse anyone (though I'm sure I'll do it anyway...)

So let us begin, where we left off last time: with the completed bowl.

Seen here: poplar top block; honduras rosewood ribs; paper rib tapes; spruce counter-cap.




This photo, and the one below, show the bowl with the false belly fitted inside. This piece of carefully-shaped 1/4" pressed board will preserve the body outline securely throughout the building process.

I've spot-glued in a few places along the side ribs to keep the false belly in place. I've used weak glue size, so that it won't be too difficult to remove the false belly when I eventually need to do so.


Here I'm marking the various depths of the 'belly scoop' on the edge rib. I will then plane this scoop evenly into the edge rib on both the bass and treble side.



I've planed in the belly scoop, and you can see how it creates a smooth curve from the bottom end, to the middle of the bowl, to the top end. 



I mark the position of the front edge of the bridge by transferring it from my working drawing. Then I stretch a length of  black thread across the body at that point, and tape it securely in place with masking tape.

I also determine the body's centreline, and tape a length of the same thread to the bottom end of the body. 
A close-up view of the crossroads.

The centreline thread is long enough that I can stretch it across the  marked centreline on the top block, and eventually use it to align the neck. 

A view from the bottom end.

After drilling pilot holes, I screw a pair of plexiglass blocks into the top block. These blocks are crucial in setting the neck at the proper angle, and keeping it from slipping forward during gluing (after the neck is shaped and veneered).

Now I can start working with the honduras mahogany neck blank.  The first step is to flatten the top surface, which I do with a low-angle block plane. (This neck blank is built up of three pieces, which were offcuts from a plank which also yielded a number of single-piece neck blanks. I glued the pieces together a number of years ago; this neck will be as stable as a single-piece neck, and will use perfectly good material that would otherwise have gone to waste.)

This is my method of determining the neck cut-off angle: I lay a straightedge from the bridge across the top block, and a sliding bevel on top of that. 

I adjust the bevel so that it matches the angle of the top block face.

A brief aside about what I'm doing here: the thread I've stretched across the body represents the position of the front of the bridge, according to the plan view; it also represents the elevation of the bridge, in relation to the edge of the bowl. Referring to my side-view working drawing, and making some careful calculations involving the height of the first string at the bridge, the thickness of the soundboard, the thickness of the fingerboard, and other factors, I can determine the angle of the top surface of the neck in relation to this string. What you see in the photo is my straightedge resting on a spacer block of a precise thickness, which I've chosen because it will allow the straightedge to rest an exact distance below the thread (which I've calculated.) 

Once I've got the angle exactly right, I can then transfer it to the side of the neck blank...

And make the cutoff by adjusting the bandsaw table to the proper angle.

I then refine this angle with a low-angle block plane and, at the very last, a sanding block. This surface must be dead flat, and I check for flatness carefully with an engineer's square.

Holding the neck in place with the left hand, I bring in a straightedge to hold against the neck surface. This allows me to check the angle of the neck surface in relation to my bridge thread. 

I've stuck a bit of steel tape measure to the corner of the straightedge, so that I can see exactly how far below the cotton the straightedge sits. I will adjust the neck cutoff as needed with the low-angle block plane, files or sanding block, until the angle of the neck is exactly what I want.

When I've got the angle, I size the end-grain of the neck cutoff a number of times with hot diluted hide glue.

I also brush a few coats of size on the top block surface. I let both surfaces dry overnight, then re-fit the next morning, making sure one more time that the angle is exactly correct.

When I've re-fitted the neck yet again, I mark the position of the neck screw by pushing a shop-made awl through the screw hole in the top block.

There's my mark.

I have a good solid jig that I can clamp the neck to, to hold it upright while I drill a pilot hole.

Your humble narrator, in action, drilling the pilot hole for the neck screw.

Once the pilot's drilled, I can screw up the neck, and bring up the thread to mark the centreline.

And once I've done that, I can lay out the edges and centreline of the neck. (As you might notice here, the centreline of the body and that of the neck do not coincide, which is often the case with 13 course lutes.)

Here's me laying out the neck shape at the nut end. Note that I will prick along the inside line, subtracting the thickness of the neck veneer.

There's my neck profile at the nut end.

And here's my neck profile at the body-neck joint. Note that I've marked an inside line here too, to allow for the thickness of the veneer.

The first step in shaping the neck is to shape the long section only.

There's the long section: note how the line quickly re-curves as it comes away from from the body-neck joint, then flattens and tapers evenly out toward the nut end.

I shape the neck using, first, a spokeshave and small fingerplanes, then the low-angle block plane, then rasps and files, as you see here.

The re-curve in the long section, along with the change in cross-section profile from a near-semicircle at the body-neck joint to a very flattened profile at the nut end, make this neck a very complex shape to carve gracefully. This photo shows the nearly-finished shape.
As a final check, I screw the neck to the body to make sure I've left the correct space for the veneer.



And then, at the end of a long, long, long, long, long, long day, I sweep up.

I hope you've enjoyed this, the second installment of "The Tedium and the Triumph." So far much tedium, not too much triumph. But it does feel good to get a good shape on the neck, and I'm looking forward to veneering the neck next week, which I'll share in the next installment.




2 comments:

  1. Mr. Carey. I like your idea of utilizing the false belly for several reasons, and determining the scoop line. Nice work! As a former pupil to J. Van de Geest, I find your methods refreshing and inciteful. Thanks for a wonderful presentation!.....James North

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