Sunday 15 February 2015

A Small Fix

I have another repair to tell you about, which I did in December, in the between putting varnish coats on a couple of new lutes (I'll tell you about them in a little while).  The repair was pretty minor, but I thought I'd talk about it because it illustrates a couple of important principles of lute making--how to make a well-fitted joint, and how to use hide glue to get a really solid bond.  These skills are applicable in many stages in the lute's construction, and every aspiring lute maker should know them.

The repair was to a 6 course lute owned by Nelson Amos, of Ypsilanti, Michigan, and as a matter of fact, it is one of mine, a lute that I built for myself in 2007.  Nelson bought it from me a couple of years ago, when I decided to make myself a new 6 course lute.  The problem: a detached peg box. A sudden wrong move, a small impact, perhaps, had knocked it out of its joint.  It looks pretty terrible, and of course the lute is out of commission until the problem's fixed, but it's really not that big a deal to put things back together.
Photo: Nelson Amos
The first thing to notice is the quality of the break itself, and the results thereof.  When the pegbox came out, it took a fair bit of material along with it on its underside; however, the back side of it is almost completely undamaged.  This suggested to me that although the pegbox was well glued underneath, the back side was not well glued at all.  In fact, on closer inspection I could see very little glue residue at all on the back side of the peg box, or on the corresponding surface of the rebate in the neck: tell-tale signs that I either hadn't fitted the pegbox well, or hadn't glued it well, or, most likely, a little of both.  
All the wood was still there, and the break was pretty clean, and I guess if I was one kind of lute-repair person, I might consider just sticking the peg box back on with some kind of modern gap-filling adhesive.  For better or worse, though, that's not the way I work. The peg box might stick, but probably not for long, and in any case the joint would look really ugly.  I like to do these jobs right, and if I didn't quite do it right the first time around,  I would happily do it right the second time.

The first thing I needed to do was repair the rebate in the neck.  The back side of the joint was fine, but the 'tongue' of the joint was quite severely damaged, with much material having been torn away.  I needed to build that area up again.  I first chiseled and filed the area back to make a flat surface, then glued (with hide glue) a new chunk of pearwood down on top.

There was also a small chip of wood that had been taken out of the back side of the peg box (proving that that surface wasn't actually completely devoid of glue after all).  I chiselled out a small channel and filled it with a slip of pear, then flattened the area with chisel and file.  I also removed the torn-out wood from the bottom of the peg box, and flattened that surface too.

Then I got to work re-shaping the rebate joint.  Most of the material I removed with a chisel, but when I got close, I used some (shop made) bevel-edge plexi-glass sanding blocks.  The bevelled edges allow me to get far into the very corner of the joint; the blocks have 180 and 220 grit paper, stuck on with double-sided tape.  (The very corner of the joint is cleared using a sharp chisel.)
 I needed to shape the sides of this piece as well, to follow the contours of the neck.
Okay, so here's the first point I wanted to talk about: how to get a well-fitted joint.  The pegbox joint can be a tough one to fit: the rebate cut in the end of the neck is an odd shape, and it's difficult to tell if the two surfaces are flat--a straightedge is of little use, especially on the back side of the joint.  So how can you tell if the surfaces are flat? 

Probably the best approach to seeing whether the surfaces are flat in the rebate is to make sure that the contact surfaces of the peg box are flat first.  And by flat, I mean dead flat--a straight edge held against the bottom of the peg box should not rock at all, whether it's held across the bottom, or along its length, or from corner to corner.  Hold the straight edge against the surface, and view with strong back lighting--no light at all should be visible between them.  (The same flatness test applies to the back of the peg box, especially where it contacts the back side of the neck rebate--it too needs to be dead flat.)

Once the peg box surfaces are flat, you can use the peg box itself to test the flatness of the bottom and back sides of the rebate.  Hold the peg box in the joint, and look at the fit--if any gaps are visible, you need to remove the material around the gap to get a close fit.  Once you've done this, though, and the fit looks good, there can still be problems--especially on the outer edges of the joint.  The only way to really test the fit is to put the peg box in place, and apply pressure to the very corner of the peg box.  With your thumb, press the peg box into one corner, say the corner on the bass side of the neck, first.  Push hard, and observe the other (treble side) corner.  Does that corner of the peg box move out of the joint at all?  If it does, then that means the joint in the corner you're pressing the peg box into is not dead flat, and the peg box is rocking a tiny amount in the joint.  The joint needs further work, with files, sanding blocks, or a chisel.

In the same fashion, apply pressure with your thumb to the treble side of the peg box, and look at the bass side.  Does the peg box want to rock outward, even a little?  If so, the joint's not flat, and you've got work to do.

Only when the peg box won't move in the joint, no matter where you press on it, is it really fitted well.

Okay, so that's the first point I wanted to make: fitting the joint really well.  The second point is gluing the joint really well.

I use hide glue for all joints on the lutes I make, which is wonderful stuff, but it requires some careful use, depending on the joint it's used to glue.  For joints that involve gluing end grain, especially, it's necessary to size the joint first--otherwise, the glue will tend to wick away, leaving the joint starved.  I think that's what happened to the peg box when I originally glued it back in 2007.  As you saw above, there wasn't much glue residue on the back of the peg box when it broke out, which suggests to me that the glue had wicked away--and the reason was, I hadn't sized the joint.

Actually, I hadn't known to size the joint.  In all the reading I'd done over the years about lute making, I had never really encountered the concept.  The book I was most familiar with, Robert Lundberg's Historical Lute Construction, doesn't mention it at all; that's not surprising, I suppose, since Lundberg didn't actually use hide glue (for the purposes of that book, at least).

I really first learned about the importance of sizing joints carefully from Grant Tomlinson, my first and best teacher in lute making.  All that I'm sharing with you here comes straight from him, so for whatever benefit you derive from my writing, the thanks should go to him.

Back to sizing: make a batch of hide glue as you would normally do, soaking the glue granules first, then heating in jar in a water-bath; then when the glue is hot and liquid, dilute it to about half its normal strength.  Brush this size on all the surfaces of the joint, on the bottom and back of the peg box, and on the bottom and back of the neck rebate.  Allow the size to dry--about 15-20 minutes--then size all surfaces again.  Size about three or four times in total, and leave to dry thoroughly overnight--then the next day, re-fit the joint again, for the final time (the sizing process will have slightly distorted the surfaces of the wood).

When the joint is perfect, you can glue in the peg box, with the assurance that the glue won't wick away from the joint.  With a peg box fitted this well, and sized this well, there should be no more problems with fragile or glue-starved joints.  This peg box joint will not fail, and that's a guarantee.
So that's the story of my peg box fix, and, for those about to fit their own peg boxes, I hope it will be helpful.  This post strikes me as being a bit text-heavy, and that's too bad, but sometimes things just need explaining and there's no way to get around it.  However, there's one last part of the peg box gluing procedure that I haven't talked about, and that's the actual gluing part--the part where glue is applied, and the peg box is clamped in place.  I won't talk about that here, but I tell you what--for those more visually-oriented learners out there, I will include as a bonus a photo of my gluing rig.  You may find information in it that's helpful in your own work.  Enjoy!