Saturday, 3 February 2018

Because You Asked: Body Frets

I recently received a request for a "how to" blog post from Mr Bill Good, and I'm going to do it.
This time out, I'm going to describe my procedure for installing body frets.

It's one of the very last things I do when I'm making a lute, or a group of lutes. Everything else is pretty much done--all the woody bits have been glued together, a nice, shiny finish has been slapped on, I've fitted a set of tuning pegs (now there's a finicky procedure), made a nut, tied on a set of gut frets, and strung up the lute. I've tuned those strings and played the first, quivering, barely in-tune notes, and an indescribable thrill has begun to form in my being as I realize, again, that I've created a living, breathing thing. The lute is alive!

The Lute Maker, in the Throes of Creation

In such a state of creative fervour--and after such a long time putting the lute together, weeks and months of sometimes very difficult, demanding work--the impulse can be to... well... get into a bit of a hurry at this late stage, cut corners a little, just tape down some toothpicks, nobody will notice, nobody ever uses the body frets anyway....

No! Don't you even think about it! Calm down--you've still got work to do. An hour's work, if you do it right, and have a procedure to follow. Here's mine.

Finding the Octave

The first thing to do is to tune that lute. And I mean tune it, pretty much constantly, for a couple of days at least. Regardless of the type of strings you've used, they'll be continuously stretching and going out of tune for most of that time. I find it useful to actually play the lute while I'm tuning--in addition to waking the lute up and helping it to find its voice, my playing works and stretches the strings so that they will fall into tune that much faster. Besides, I'm a lute maker, it's my job, and I have built this thing to make music--at this point, what else would I rather be doing?

Once the strings are really well in tune, you need to find the octave, the point approximately halfway up the string where the 12th fret will be located. It's not exactly halfway as measured by a ruler--because of the physics of string stretchiness, the octave will always be somewhat less than half the distance between the nut and bridge. (Depending on a few different factors, the octave will be probably be approximately 1.5 to 2mm shorter than half the measured distance.)

How to find the octave? Allow me to demonstrate. This is a lute that I recently repaired--not one of mine, but one made in the early 1980s by a maker in British Columbia. Like many lutes of that vintage, the fingerboard had warped a bit over the years, and needed to be re-shaped in order for the lute to be playable. In order to do the re-shaping, I had to remove all the tied frets as well as the body frets that were on the lute. Now that the work on the fingerboard was finished, I needed to put a set of new body frets down. (By the way, the gut frets I've put on are placed provisionally, and will be adjusted when I find the octave and calculate all the fret positions.)

I have a small ebony body fret that I have shaped and keep just for the purpose of finding the octave (I'll talk about how to shape these body frets in a minute or two.) I put the fret down on the belly under the top string, and strike a note.

I move that fret up and down the string, making slight adjustments one way or the other, plucking notes until I've found the true octave. I use an electronic tuner to do this (because I am lazy), but if you're a purist you could probably do it by ear, comparing the fretted note with the natural harmonic produced at the 12th fret. Whichever way you do it, when you are convinced that you've got that fret and that octave in the right place, take a very sharp but not very hard pencil (HB works well), and make a crisp, light mark on the soundboard on each side of the fret. Move the fret away. Then, between those two marks, make another mark exactly in the middle. That is the precise position of the octave.

Next, get out your ruler, and underneath the top string, measure accurately the distance between the octave mark you've just made and the front edge of the nut. Now, double that number: this gives the lute's playing string length. Use it to calculate the position of all twelve frets, according to whatever system of temperament you are using (this lute, a 9 course, will be fretted in equal temperament.) Cut a piece of card stock about an inch wide and a bit longer than the length of your octave, and carefully mark out the fret positions on it. You'll use this card to lay out the positions of the body frets (there will be three on this lute), and to adjust the positions of the tied gut frets on the neck.

I also write down on this card the diameters of each of the tied frets, and when I'm done using it to lay out the body frets and adjust the tied frets, I put it in the lute case and keep it there. It's very handy to have when replacing worn out gut frets.

Making the frets

After erasing the marks I've made on the soundboard, I lay a strip of 1/2" masking tape down on the soundboard, so that the inside edge is more or less in line with the edge of the fingerboard (the strip of tape isn't quite parallel to the first course, but flares a little.) This tape will mark the location of one end of each of the body frets, so I lay my fret card down alongside it, and mark the locations of the body frets on the edge of the tape--like so:

I can then get out my ruler, and determine the length of each of the body frets.

I want this 12th fret to cover the first three courses (the 11th fret will cover 4 courses, and the 10th fret will cover 5), so I measure the distance between the edge of my masking tape and the mid-point between the 3rd and 4th course. (You can see my mark on the masking tape on the left side of the ruler; you can also see the length of this fret will be 33mm.)

On this lute only the 11th and 12th fret will be on the belly, and the 10th fret will be on the fingerboard. In order to determine the length of the 10th fret, I need to measure from the fingerboard edge to the mid-point between the 5th and 6th course. You can see the fingerboard edge clearly here: the length of this fret will be 51mm.

Once I have the length of the frets figured out (and written down someplace), I can decide on the thickness of frets that I want to use.

This can be a bit of a tricky calculation, and it deserves some thought. The thickness of the body frets you use will depend partially on the thickness of the tied frets on the neck, and partially on how much and how quickly the belly slopes down and away from the strings, once you get past the body-neck joint. The slope of the belly at this point depends on the amount and severity of the "belly scoop" that the luthier has planed into the edge rib of the lute: some makers like a deep belly scoop which slopes quickly away from the fingerboard, while others prefer a more gentle, gradual slope (that's generally the way I like to do it, and that's the way the maker of this lute decided to work.)

Let me explain how I decided on body fret thicknesses for this lute. My general method of fretting a lute (which I normally use unless a client asks for a different setup) is to begin with a thick fret for the first fret--say, 1.05mm for the first--and then gradually tie smaller frets all the way up the neck. So, for a 9-fret neck like this one, this is how the tied frets go:

1st: 1.05mm
3rd: 0.95
4th: 0.90
5th: 0.85
6th: 0.80
7th: 0.75
8th: 0.75
9th: 0.75

The 10th fret is my first wooden fret and it will be on the neck, so  I will make it 0.75 thick as well, to give some uniformity of "feel" with the last three tied frets. Then, because the next two frets are on the belly--which is gradually sloping away from the string, and creating a bit more clearance--I will grade the 11th and 12th slightly thicker--0.85 for the 11th, 0.95 for the 12th.

Now let's make some frets.

I make fret blanks out of ebony and english boxwood, two very hard woods that will withstand years of playing, and generally choose the light or dark wood depending on the overall look of the lute. (On this lute, the original body frets that I removed were ebony, so that's what I put back on.) I make my body fret blanks 1.4mm wide, and I'm able to thickness them quite precisely to various thicknesses, as you can see in the photo above. This is the tool I use to size them up, a pull-through scraper:

I have described this tool and its use in detail in a previous blog post from a few years back. You can visit that blog post here (you'll need to scroll to near the end of the post.) It's well worth a look--I use this unit to make sets of rib spacers, ebony edge bindings, strips for striped veneers, and much more. It's an incredibly handy tool in the lute maker's workshop.

I take the blank of desired thickness, and cut a segment 3 or 4mm longer than the final finished length. Then I dress the edges of the fret, using this jig, held in a benchtop vice.

It's just a piece of particle board with some arborite on top--I think it came from a piece of old kitchen countertop. The arborite edge is nice and sturdy for holding the fret. I have a thin piece of some kind of plastic sheet stuck down on top with 2-sided tape, forming a ledge that's as wide as the fret, where I can hold the fret securely while working it.

With a #2 flat file, I break the top edges on both sides of the fret. I file them at about a 45° angle, then round over the two new edges I've just created. I'm careful not to go over onto the top of the fret--I don't want to lower it, I just want to make those edges comfortable to press a string down onto.

Then I relieve the sharp edges at the end of the fret. I put the end of the fret at the edge of my jig, and with my #2 file, give a quick downward stroke to put a 45° angle on it. Then I relieve the edges on that angle by trailing the end of the fret across the file. I then cut the fret to its final length with a sharp chisel, and dress that end of the fret in the same way. Here's how the fret ends up:

Now that I've got all the frets made, i can finish laying them out.

Laying out the frets

I need full access to the end of the neck and top of the belly to lay out the frets, so I unstring the lute. I just loosen off all the strings without removing them from their pegs, and tie them away from the top of the soundboard.

I lay down the frets in their approximate positions, according to the marks I've put on my long piece of masking tape. I then stick down smaller pieces of tape at the other ends, and bring back my fret card to mark the fret positions on them. Then I move the frets away, and use my small ruler to draw a faint line on the wood of the belly from the mark on the treble side to the one on the bass side.

I then use a small, sharp, curved scraper to scrape away the lines I've just drawn. I'm not really scraping away very much wood--mostly just a thin layer of finish on the belly and neck so that the glue I use to stick the fret down will adhere to the wood below.

Gluing the frets

I use hide glue for this job, as I do for all the gluing jobs on a lute. You might be tempted to use yellow carpenter's glue for this, which would be fine, but I find that hide glue tacks faster and cleans up better--instead of waiting overnight for yellow glue to dry, you can use hide glue and be playing again in an hour.

I use a fairly thin glue for this job--you don't need a lot of glue to get these frets to stick. 

I wrap a little two-sided tape around the end of a small dowel, and just press that down onto top of the fret so I can lift it and hold it over the glue pot while I brush some glue on (the more dextrous among you could probably just as easily use tweezers for this job.) I just dip the brush in the glue, sweep upward onto the fret, then sweep back down to brush off excess. Then I stick the fret down quickly in position--locate one end of the fret close to its mark, then bring the other end down. It should be good--if not, adjust. Hold the fret down for about 30 seconds, until the glue begins to set. 

Then bring in the small metal ruler, and use it to press the fret down until the glue is well set (a minute or two of pressure should be good.)

Then move on to the next fret, and go through the same procedure, then the next. By the time you've got all three frets stuck down, the glue will have set well enough on the first one that you can go back to it and clean up the squeeze out. Just brush a little cold water on each side of the fret, give it a minute for the glue to soften, and clean up with a sharpened spruce stick. For a last measure, give each fret a quick wipe with a damp bit of paper towel, to remove any glue residue that might be lurking on the top of the fret.

And that, my friends, is that. Remove the masking tape bits, and start the process of tuning the strings. By the time the lute's back in tune, the body frets will be firmed up, and you're ready to play again.

So that's my procedure. It took a long time (and a lot of photos) to describe a fairly simple operation. Still, some might object that I go too far--that all this rounding and filing and fiddling is simply paying too much attention to a feature on the lute that isn't, after all, that important. To which I would reply: there is no detail on a lute that is too small to pay attention to. And in the case of these body frets, a lot rides on their position and shape. If they're not in the right place, the intonation will be wrong. If they're left square-edged, the note will sound thin, but more to the point (ahem), they will feel unfriendly to the fingertips. I've tried many lutes that had body frets with edges left square, and I've always had the uncomfortable feeling that I was stubbing my fingertips on them. Why would I want to leave something unfinished on the lute that I felt was impeding my playing?

When players and makers think of "playability", they're mainly thinking of big things like string spacings, action (string height above the fingerboard), fingerboard arching, and neck shape. But I would argue that apparently "small" things like body frets can make a significant contribution to playability too. There are a few other small details of finishing a lute that make similar contributions; perhaps I'll make them subjects of future posts.