Sunday 8 September 2019

Building a 13 Course Lute, Start to Finish, 4: Gluing on the Neck

Hi, and welcome back to the series!

In this instalment, I want to detail how I re-fit and glued the veneered neck to the body of this 13 course lute. As I explained at the tail end of the last episode, hide glue contracts as it dries and hardens, which can be a difficulty in working with it, but also a benefit in certain situations. We'll see those two properties of hide glue demonstrated in this episode.

By the way, to clarify, when I talk about 'hide glue' on this blog, I am always referring to hot hide glue, the stuff that's sold in granular form and must be soaked and then heated in a water bath to use. It is the only glue that I use in building my instruments.

The granules

The heated glue

As I mentioned at the end of the last episode, I set this neck aside for a week after gluing on the veneer, because it takes that long for the glue to dry completely and for the neck to stabilize. It's a big surface area--the biggest, or at least the widest, glued surface on this entire lute--and while it dries, the hide glue tightens like a fist. The whole area covered by the veneer shrinks, and pulls the edges of the neck downward; the result is that the top of the neck, which was dead-flat when I first fitted and shaped it, is now humped pretty significantly both across and along its surface, about 1mm in both directions. (It doesn't sound like much, but in this situation, that's pretty significant.) I'll need to flatten it before I can re-fit the neck to the body, and then eventually glue it on.

I'll also need to flatten and re-fit the neck-joint surface, which I sized with weak hide glue during the veneering process. (Its profile is actually a little concave right now.)

The way I flatten the top surface is with my trusty low-angle block plane, planing from the outer edges in toward the middle of the neck. I do some of the trimming with the neck off the body, but most of it I do with the neck fitted up, just because it's a lot easier for me to handle at the bench.
As you saw in earlier posts, this is how I check the angle of the neck in relation to the body--with a long straightedge held against the top surface of the neck, viewed in relation to a thread stretched across the body at the bridge position. This is why I need the top surface of the neck to be flat--so that my straightedge will register cleanly against it.

I also check the alignment of the neck with my centreline thread. 
The alignment looks pretty good. Remember, on this 13 course lute--and in fact most wider-necked lutes--the centreline of the body and that of the neck do not coincide (the neck is usually 'tipped' a little toward the bass side.) In this photo you can see the pencilled neck centreline, but the body centreline is covered by the thread that I'm stretching up from the bottom of the body.

Looks good down at the body-neck joint too. You may notice in this picture that I haven't flattened the entire neck surface--I've really only paid close attention to flattening the outside edges, which is where I hold my straight edge to check the neck angle. The upper neck surface actually remains a little humped-up in cross section (and as long as the alignment and neck angle are good, that won't bother me a bit.)
Here my neck is fitted, and I'm getting ready to glue. Since the pencil mark I've been using to align things is going to be obscured by glue squeeze-out, I need a better, clearer way of marking neck alignment when I glue up. I put down a strip of 1/2" masking tape across the joint...

And then cut the tape in two with a knife, right along the joint. Then I can unscrew the neck from the body, and get ready to glue the neck in place.

Here's what I'm looking at just prior to gluing. I'll warm both surfaces with a hair dryer before brushing glue on both surfaces.

Here's a wider shot of the gluing situation, courtesy of my A/V assistant, Carl, whom you met in the previous instalment. I'm about to do a rehearsal, a dry run. When I go for real (in about twenty seconds from now), I'll warm the surfaces, brush glue on both surfaces, rub the joint slightly to get good contact, make sure alignment with the tape is correct, and then twist the screw home.

The immediate aftermath, showing the tape alignment and glue squeeze-out. Rather than clean up the excess glue, though, I will actually add to it, by painting more full strength glue along this glue line...
And on the backside of the joint as well. Here is where we see the beneficial aspect of hide glue's tendency to shrink as it dries--the drying glue will contract and pull the two edges of the joint together, providing external clamping pressure (along with the internal pressure applied by the screw.) I will actually paint more hot glue on the outside of the joint a couple of times over the next few minutes, to create more concentric layers of clamping pressure.

I don't hang the lute to dry, but prop it up gently instead.

Next morning: here's my result. The alignment looks good, and the joint looks tight (though again, you can see where the middle of the neck surface is a bit humped up in relation to the top block.)

I usually use a piece of paper towel to clean up excess dried hide glue. I wet the glue first, then lay down paper on it, then re-wet the paper as need arises over the next 15 minutes or so. 

By then, the glue is soft enough for me to clear away with a sharpened spruce stick.

Here's my joint: the alignment of veneer and ribs looks fine. Not perfect--such a joint only rarely comes out perfectly, and there is generally always some filing and rectifying of either the veneer or the ribs to be done. But this looks good. 
So for the time being, I'll hang this one with his fellows (an 8 course on the left, 7 course on the right, both also with veneered necks). By the way, at this point I will not re-check the alignment of the neck, either with my centreline string or my straightedge and thread--there will be plenty of opportunities for me to check those things a little farther down the road. For now, I've got bigger fish to fry...

Or should I say fish bellies? In our next episode of 'The Tedium and the Triumph,' I'll let you know how I go about thicknessing these flounders--and preparing them for carving their roses.

Before I sign off, I'd like to thank everyone who got in touch with me after the last blog post, where I expressed some misgivings about my (rather exhaustive) sharing of my working techniques in building a 13 course lute. Three people in particular helped to clarify my thinking, and I hope they don't mind me mentioning them here--Grant Tomlinson, Bill Good, and Bob Eby. Just share, they said, and don't worry about it. So that's what I'll do. Thanks.