Saturday, 19 October 2013

Because You Asked: Making a Lute Mold (6)

Hi again.  Today's the last installment in the series of how to make a solid lute mold.  We've built a big block of wood, carved it down into a shape, drawn rib lines and carved rib facets--all we have to do now is refine these lines and surfaces until we're satisfied. 

Simple enough to say it, but in practice I've found the refining to be a very long process.  It demands a lot of concentration, decision making, and intentional looking--from different perspectives, in different kinds of light.   It also requires you to mentally step away from the fact that you're sculpting a shape, and think, instead, of how bent wood ribs will actually fit together on the mold.  The fact is, you can stop work on the mold anytime you like, and make your mold any shape you want, but it doesn't necessarily follow that your mold will be easy, or even possible, to build on.  With that in mind, what I want to do today is give some techniques and hints to help you get a good-looking and practical shape for your mold.

The first thing to remember throughout this process is not to try to do everything at once.  Instead, think of working through drafts, or versions, of the mold.  What we have right now is a first draft (and a rather lumpy one at that.)  We'll do some shaping, remove a modest amount of material, then have a careful look at the whole.  We'll make some decisions, then go on to a second draft, where we'll do the same thing.  All the time, we're thinking of moving toward a shape--not just landing there, but moving toward it in careful steps.

In general, it's best to be conservative at this stage.   It's much easier to remove material from the mold a little at a time than it is to add material if you've gone too far.

Refining the Rib Lines
You'll remember that before we put in the rib lines, while we were still working on the overall shape, I suggested that it was natural and desirable to leave the surface of the mold slightly 'humped up' between cross sections.  I also said that eventually we would be bringing down these areas in a very controlled way--and that's what we'll do now.

The best way to see these humps between the cross sections is by looking at each rib line separately, not from the front or the side, but directly across the rib line--from above, with a strong light (your bench lamp) above you, and all other lights shut off.  You can also lay a dark cloth on your bench below the mold, to provide a contrast against which the rib line will stand out.

Sighting across the rib line, you'll see a series of humps between the cross sections.  This is good.  The idea now is to lower those humps gradually and create a smooth, continuous line.  To do this, use a sanding block (with, say, 180 grit paper) to gently take them down.  Be careful not to sand down your cross sections--these should be preserved.  Sand off only material between the cross section lines.

It's best to have a plan of attack when you're doing this work, rather than just randomly sanding away at various rib lines.  Here's how I proceed:  I mentally divide the mold into quadrants--treble and bass sides in front of and behind the largest cross section--and I begin by working with one front quadrant, then the other, and then one back quadrant, then the other.  I might work from the outside rib in toward the middle, then from the middle toward the outside rib.  However, even though I'm working on one rib line at a time, and one quadrant at a time, I'm always keeping an eye on the whole, trying to see how the rib lines are shaping up all over.  

Here's a look at the mold after we've had a go at all the rib lines.
You can see that where the rib lines have been sanded and flattened, the pencil line has been obliterated.  However, the tattooed pin holes are still clearly visible.  With your flexible curve, re-establish the pencil rib line; then as before, use your finger plane and curved scraper to remove material between the rib lines, to establish a good flat surface between them.

That's round one.   How's it looking?  A bit less bumpy, a bit more streamlined?  Good--we're making progress.

Now take some time to really look at how the mold is shaping up.  Look not only at the rib lines you've been working with, but also the facets you've carved between them.  Look at each one separately: does the shape curve gracefully, curling and flattening in an organic way?   Sight across each facet, from one rib line to another: are there bumps on one side that don't match the other?  In other words, will you be able to bend a strip of thin wood to a shape that will fit that facet closely?

Turn on the overhead light, then turn it off again.  Use your bench light to highlight certain spots; then back it off to get a good sense of the whole.  Walk to the far side of the room, then come close again.  Turn the mold around, look at it from above, behind, in front, below.  Take the mold over to the window, and look at it in natural light, both direct and indirect.  Think.  Brood.  Sigh.  Furrow your brow.  Scratch your chin.  With a pencil, and mark some spots where you might want to flatten the rib lines further.  Then take a deep breath, take up your sanding block, and go on to draft number two.

A Couple of Tools
A couple of tools that will make your life easier at this stage are a contour gauge and a sliding bevel.

The contour gauge allows you to take an accurate impression of a curved shape.  It's useful in two ways: first, it allows you to compare contours from one side of the mold to the other; second, it can sometimes show a hump or a bump more clearly than just looking at the rib line itself.  This is especially true if you're trying to get a smooth transition over one of your cross section points, where the rib line tends to hump up on each side.

(By the way, comparing rib lines from one side of the mold to the other likely won't give you an exact match.  That's to be expected, and it's not a problem, as long as the shapes are comparable, and good on each side.)

The second handy tool is the sliding bevel.  This tool allows you to look at the angle formed by the outer rib and the bottom of the mold.  That angle will obviously change as you go from the widest point forward, or back; the sliding bevel will help you judge whether the rib angle is changing gradually and gracefully.  It will also allow you to compare the rib angle from side to side on the mold.

The sliding bevel is perhaps most useful around the bottom of the mold, as you develop the shape of the capping strip.  Again, the angle changes as you move around the mold, but the angles should be similar from one side of the mold to the other.  

The Bottom of the Mold
The area back of the widest section is the most difficult part of the mold to shape.  All you have to guide you is the longitudinal section; every thing on either side of that is up for you to judge.  It helps if you have a good set of photographs of the original lute body you're working from, showing the bottom section from various angles, but you might have only a photo of the side view, and another of the whole back.  Or, you may not have any photos at all.  In any case, while it's true of the mold as a whole, it's especially true of this part of the mold: you are a sculptor, and you have to imagine this shape into being.

I can't say that much to guide you here, except to re-emphasize the principles I've given already--remove a little wood at a time, try to see the back area not in isolation but as part of the whole, and at the same time pay attention to individual facets, to judge whether you will actually be able to bend a rib into the shape you've made.  One other general principle is that of all the ribs, the center rib will likely be the one to have the sharpest bend at the bottom end.  All the other ribs will have a somewhat shallower bend, and they will likely become a little shallower the further they are away from the center.

The Capping Strip
Maybe the best way to help find a shape for the back end of the mold is by setting up the capping strip.  We've already put in a pin line to show its location (remember, we did this when we first set up the rib lines)--now, let's draw it in fully, and do some work to integrate it into the mold.

Once I've drawn in the location of the capping strip, I flatten the whole area, from the top of the capping strip to the very bottom edge of the mold.  Why do that?  Won't that spoil the nice rounded shape at the bottom of the mold?  Well, it will, but the fact is that once I actually get around to putting a back together on this mold, I'll need to flatten the ribs in that area anyway to create a gluing surface for the capping strip.  If I flatten the area on the mold first, then when I put the back together I can bend the tips of the ribs to follow that shape.  I'll be giving myself a head start in my flattening work, and I'll also save having to remove a lot of rib material to do it (which might otherwise thin out and possibly weaken the ribs in that spot.)

The more you refine the capping strip area, and the rib lines and facets leading up to it, the better idea you'll get of the shape of the whole bottom end.

Things are starting to look better here.  I can't remember how many drafts I went through on this particular mold to get it to this shape, but it was a few.  Each time I touched up the rib lines, and each time I flattened the facets between them, my work got more and more precise, and the mold got more and more refined.

Late-Stage Chores
As the overall shape evolves, and comes close to what you might hope is a finished shape, there are a few late items to pay attention to.

Keep refining the top block, but when the shape gets very close to finished, switch to working with a file (a #0 Grobet file works well), and file from the mold onto the top block.  Remove the block to have a look at how close you're getting to the marked cross section here--you should be very close indeed.
Another late-stage task is to scrape the facet of the center rib.  You'll remember I advised to leave that one alone for as long as possible, to preserve the longitudinal section you built into the mold.  At a certain point, though, hopefully when the mold is very close to its final shape, that longitudinal section needs to be scraped away, as the center rib takes its place as just another of the ribs on this lute mold.

While we're on the subject of scraping facets, another important late chore is to hollow-scrape the facets between all the rib lines.   Up until now we've been content to scrape them reasonably flat, for the purposes of carving a good overall shape.  However, we now have to take this scraping a step further, in anticipation of actually fitting a bent rib against the mold.

One characteristic of ribs bent with dry heat is that they tend to go somewhat concave across the width.  This makes for a really cool look on the finished instrument, but it can make for some difficulty in fitting and gluing ribs--unless you account for it on your mold.  That's what the hollow scraping is for.  The wider the rib you're working with, the more concave it's likely to go, but narrower rib facets--like the ones I'm working with here--need to be hollow scraped too.  Check with a straight edge all over the mold to make sure that they are.
Beyond the Theoretical
At this stage, your mold is very close to being finished--you've used the cross and long sections you built into the mold to carve yourself an elegant shape, with graceful, flowing lines.  But what if, after all this work, and all that careful attention you've paid, the lines aren't graceful, and the shape isn't elegant?  Well, the short answer is: you've got more work to do.

You may have gotten to a point where the practical shape of the thing you've made bumps up against the theoretical shape you're working with.  In other words, the cross sections you designed in two dimensions on your drawing just haven't translated well to three dimensions on the mold.  That's okay--it happens.  Usually, for me, the problem has been that I've ended up with a shape that's a bit too big and boxy on the front end of the mold (the area approximately behind the rose on the finished instrument.)  I'm not too upset if that happens, because it just means that I have a little more material to remove; it would be far worse if the area was designed too small, because once the material is gone, it's difficult to put back.

If this is the case for you, and you've got more material to remove, then just do it the way you've been doing it so far--a little at a time, working both sides of the mold evenly, keeping an eye on the flow of the ribs, as well as the overall shape.  You'll get there eventually.  I've found that when I'm working the area behind the rose, it's very easy to go too far, and to weaken it (I mean visually, not structurally), so do be careful.

The Finished Mold
The mold is finished when you declare it to be--when you're either satisfied with the shape, or you're so sick of working with it that you can't bear to look at it anymore.  (They might be the same thing.)  Here is the final shape of my mold.

I think this shape looks reasonable--reasonable enough, at least, for me to build a body on it, which is after all the only real way to tell if the mold is good or not.  If it builds a good-looking back, then I'll be satisfied; if it doesn't, then I'll work on it some more before building on it again.  Most of the molds in my shop have been works-in-progress; some have gone through numerous versions before reaching their final shape.  I'm looking for a shape that's practical, but also beautiful, and sometimes those qualities can be elusive.

You can see in the photos above that I've done a couple of things to finish up: I've inked the rib lines, and numbered the ribs.  You can number them consecutively if you want--I prefer to number the ribs separately on the treble and bass sides from the center rib out (i.e., 0 in the center, then T1, T2, T3, on the treble side, B1, B2, B3, on the bass, etc.)  I find this system helps me keep things straight as I'm working outward from the center rib when building the back.

Here's another hint--cut some strips of mylar, stick them down with double-sided tape, and trace the pattern of the rib.  A set of these rib patterns is very handy to have when you're laying out shapes on your rib material. 

One last thing to do is give the mold some kind of finish: two or three coats of a spray-on lacquer sanding sealer work well.  (Remember to remove the top block before you do it!)

You are now well and truly done your lute mold, and you have my congratulations in advance.  Take yourself out for a refreshing beverage of your choice--it's on me.  Don't overdo it though--you've got a lute to start building in the morning.

* * *

And there you are, for those who asked (and those who didn't): this is how I make a solid wood lute mold.  I told you it was complicated!  Perhaps it's unnecessarily complicated; no doubt there are many ways you can find to do this more simply, or more efficiently, or more precisely.  I encourage you to experiment, and find the method that works best for you.  If you have the time, I'd like to hear from you--let me know what your experience is like using this method, or if you've come up with ways to improve the process (I'm a fan of those who betterize.)

I hope this is a help to lute makers, especially those who are starting out.  When I was building my first lutes, there wasn't much information around on how to make this kind of mold.  I don't think a solid wood mold is necessary for all kinds of lutes, but for some of the more complex shapes of certain lute bodies,  I think a solid wood mold is indispensable.

Still, while it's a very important part of the process, making a mold is really only a small part of the total work of making a lute--and after all, the whole lute is the true test.  The mold shown in the pictures I've used for this series is for a 12 course lute that I made in 2012.  How did it turn out?  You can judge for yourself--here's the lute's happy owner, Evan Plommer, favouring us with a tune, his own lovely setting of Walsingham.

Until we meet again...


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