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...


Sunday 6 October 2013

Because You Asked: Making a Lute Mold (5)

Last time we met, we had turned the very rough shape of the glued-up mold into something vaguely resembling a lute. Today we'll continue refining the overall shape, and then at a certain point, we'll mark out the rib lines and begin to think of it not just as a shape but as a mold--a sculpted object upon which separate pieces of wood will be glued together to make a lute back.

Refining the Shape
Two tools will make our work a lot easier.  First, a small curved finger plane is very useful for carving the top block; for most of this work, the plane cuts best working uphill, that is, from the tip of the block back toward the mold. 

The second tool is a Veritas low-angle spokeshave, available in Canada from Lee Valley Tools.  This  tool can be set closely to take very fine cuts, and it works well across the grain as well as on end grain--which we have to deal with down at the bottom end of the mold.
I've evolved a way of holding the tool so that the left hand is a guide, while the right hand supplies power.  I hold it lightly but firmly, and take fine, quick cuts.  Most of the time I'm working out and downward, from the middle of the back out toward the edges, cutting directly across the grain of the wood.  I try not to dwell on one area too long, but keep moving and refining the entire shape of the mold.

These next two photos show the kind of progress that you can make with these tools.  The first shows an overall smoothing both on the mold and on the top block; the second photo shows how I've used the spokeshave directly over the cross section to carve things down in a controlled way.
We've almost taken down the overall shape to the cross section lines, but not quite.  We need to go a little farther, and get a little closer.  Something like this:
That's close.  Notice, though, that you can still see the cross section, and you can still see the rib location points that I marked on the beveled edges of the cross section blocks before I glued up the mold.  Okay: I think we're almost ready to start laying out rib lines, and carving rib facets into our mold.

Once we start doing that, however, we will have to say goodbye to our cross section lines, because they are going to be (mostly) carved away.  We'll need to mark our rib location points so we can find them again as we work.  Here's how.

Take a sharp pin, and prick each rib point deeply.
Then take a felt-tipped pen, and press it into each pin hole.  By doing this, you're actually tattooing the rib points, ensuring that you can find them easily throughout the rest of the carving process.

Laying out the Rib Lines
To lay out the rib lines on your mold, you need to connect the dots--all of the rib points on each of the cross sections in your mold--from the very tip of your top block all the way back to the bottom end of the mold. 

The ribs are laid out on the face of the top block using a template derived from your cross section drawing. Notice how I've used a chisel to chamfer down to the line here, just as I did on the cross section blocks of the mold.
On the bottom end of the mold, you can use your cross-section drawing to lay out the orientation of the ribs as they disappear under the capping strip (in fact, you can lay out the location of the capping strip at the same time as you mark out the ribs.)

Use a pin prick through the drawing to show the location of each rib line below the capping strip.

Now, to connect the dots and make an accurate rib line, you'll want to make yourself this very handy tool.  Take a thin, flexible strip of plexiglass, between about 15-20 mm wide, and about 70 or 80mm long.  Scribe a straight line down the center of it, and every 10mm or so, drill a small hole for your marking pin to fit through.  Take this marking strap to your mold, and set the scribed line over the dots of one of the rib lines from the top to the bottom (you can fix the strap in place with pins).
When everything's aligned correctly, use your marking pin to prick through the holes into the mold.  Then remove the marking strap, and tattoo the pin holes with a felt-tip pen. 

All that's left to do now is to connect these tattooed dots, and I do this with a sharp, hard pencil and a flexible curve laid on its side.  (You'll need to cut away the inking 'lip' on the side of the flexible curve for it to lie close to the mold so you can mark an accurate line.)
Here are the rib lines, neatly laid out. 
I like using the marking strap and the flexible curve, rather than just the flexible curve, because the marking strap ensures that I'm creating a single, continuous line.  Because it's too short to reach over the entire length of the mold, the flexible curve by itself can only give segments of a line, with no real guarantee that the segments will align well.

Creating the Rib Facets
Now that the lines are laid out, the mold's facets can be carved.  This operation is pretty straightforward: all we're doing is removing material between the rib lines.  As long as you can plane, and scrape, between the lines, you'll be fine.

For removing the bulk of the material, you can use your small finger plane.
Just a word of caution though--you should leave the center rib, with our longitudinal section, unplaned for now.  We'll need the long section for reference for a little while longer.
Once you've removed most of the material between the rib lines, you can start working with a curved scraper to really flatten the facet.  You should scrape pretty much right out to the rib lines, and the facet should be quite flat between the rib lines.

Down at the top block we can really start to do some very accurate work as we shape up the rib lines and facets.  You might remove the top block and chamfer down to the cross section line on the front of the mold:
Then replace the top block, and chamfer the back edge of it to match.
As for the bottom end of the mold, you should stop flattening the facets of the ribs as you approach the top edge of what will be the capping strip.  Instead, use your finger plane, scrapers, files and sanding blocks to flatten the whole capping strip area.
I think this is a good place to stop for today.  We've taken the rough shape and refined it; we've laid our our rib lines and capping strip, and the project's actually started to look a lot like a lute mold.  Next time out, I'll discuss some ways we can refine the shape further--and further, and further still--until we reach a point where we can do nothing more, and we declare our mold finished.

The part of the process that we've just begun, of carving and refining, takes a long time, I've found, and a lot of concentration and stamina.  Have a good sleep and eat a good breakfast, and I'll meet you back in the shop in the morning.

Thursday 3 October 2013

Because You Asked: Making a Lute Mold (4)

When last we spoke we had glued up all the pieces of the mold-in-progress, shut the lights off, closed the shop door, and with a very satisfied feeling gone home for the weekend.  Now it's Monday morning and we're back at the shop, ready to get carving!  Well... not quite so fast.  There are a few technical 'housekeeping' items that we need to get done before the real shaping of the mold can begin.

The Clamping Channel
After removing all the clamps and screws, the very first thing I do is to cut a channel in the lower end of the underside of the mold.  This is the channel used for clamping the capping strip, when it's glued on late in the process of building the lute back.  You can cut this channel at practically at any time in the mold-carving process; I prefer to do it now, when the back's not yet been carved into a slippery, roundy shape, and it's much easier for me to clamp it securely upside down on my bench.
 I draw the outlines of the channel--
And then I cut it with a few passes of a plunge router.  The channel will eventually be between about an inch and a half to two inches deep, depending on how wide your capping strip is.
Trimming the Excess
Once that's done, I can start working with the shape of the mold.  First, I take it to the band saw and cut away most of the wood that's overhanging the base plate.  You can't really mark a line on top that you can cut to with the saw, but it's easy enough for you to see where the saw blade is in relation to the base plate so that you don't go sawing into it.
There we are: our basic shape.  Let's take a quick look at some of our glued joints.

This is the result of all that marking and carving we did--our cross sections and long sections are plainly visible and ready for us to carve to, and the rib lines are marked out too.

The Belly Scoop
If you want to integrate the belly scoop into the edges of the mold, now's a good time to do it.

If you aren't familiar with the term, the belly scoop is the gentle curve that's planed into the edge ribs of the lute back, so that the belly (when it's glued in) dips a little toward the middle and rises toward the ends.   A common feature of historical as well as modern lutes, the belly scoop serves a couple of purposes: it creates a bit more space between the strings and the belly out in front of the bridge (where most of the plucking gets done), but more importantly, it also stabilizes the belly to help guard against distortion caused by string tension (like the kind of 'potato chip' profile one sometimes sees on the soundboards of guitars.)

Depending on the size and type of lute, the belly scoop will probably be somewhere around 3 to 3.5mm at its deepest (the center of the body), tapering out to zero at both ends.  I first draw the curve on paper, laying it out on a grid; this allows me to measure the depth of the belly scoop at specific points, and to transfer that depth to the edge of the mold, using my sharp dividers.  I can then plane a bevel into the edge of the mold, connecting all these points and creating a gentle dip in the outline of the mold.  (When I've assembled the lute back, I can then mark the belly scoop accurately on the inside of the outer ribs.)

The Mold-Holder
In order to carve the mold efficiently, we need to mount it on some kind of vise or block system.  Whatever we use, the hold needs to be firm, but it also needs to release quickly so that we can tilt the mold and work on different areas.  I've seen some very slick-looking universal-joint carving vises people have made (or bought) to hold their work; I use a very low-tech system of a block screwed securely to the underside of the mold, held by a large, heavy clamp, which is itself set into a built-up plywood block and held in my bench vise.  Have a look.

(By the way, these are photos of a different, finished mold.)

Note the bolt that I've inserted into the clamp's wooden handle.  This is my tightener and quick-release, and this system would not work without it.

I like this setup because it allows the mold to readily tilt toward and away from you, while the tip of the mold can be raised or lowered simply by releasing the bench vise.  (To spin the whole thing end-for-end, you actually need to lift it out of the vise, turn it around in your hands, and set it back into the vise.  Not the most convenient manoeuvre, but I've learned to live with it.)

The Front Section
There's one cross section that we haven't drawn in and carved down to yet, and that's the section at the front of the mold.  In fact, we've left a little extra material here on purpose, so that we can plane the face of the mold after everything is assembled.  Let's do that now.

You can chisel a rough profile first--
Then flatten off the front with a low-angle block plane.  This surface should be dead flat and perpendicular to the bottom of the mold.  When it is, you can use your drawing to lay out the section profile and rib lines.
Notice how the cross section matches exactly the long section point that's already carved into the mold: that's a very good sign that we've been doing accurate work, and that all our profiles are matching up closely.

Rough Carving
Before too long, we'll need to fit up a top block to the front of this mold.  However, at this point we can begin to do some rough carving to whittle this big battleship down to something more closely resembling a lute.

Begin with a large, sharp chisel, one inch wide or more, and take fairly gentle paring cuts, either across or slightly askew the grain of the wood.  The cleats you left on the sides of the blocks should come away easily, and in a while you'll start to see a rough shape emerging. 

As we carve, we're keeping in mind our cross sections and long sections, using them as our guides.   We can begin to cut down to them a little more purposefully by using the chisel directly over the sections, carving directly across the grain.
You'll notice that as I'm carving down to the lines, I'm allowing the wood in between the lines to remain a little humped up.  It's a natural tendency as you carve, and you should go with it--as we continue to refine our carving we'll be taking down these humps in a very controlled way. 

The Top Block
This is the 'nose' of the mold, the block onto which the ribs will be glued as the lute back is assembled.  It therefore needs to be separate from the mold, held securely but detachable from it.

I use poplar for a top block, and I attach it to the mold by means of a plate screwed up to the underside of the mold.  The plate is birch plywood, and it's held to the mold by #10 screws.  I screw the top block to the plate with 1" #8 screws.

Of course, the bottom surface of the block needs to be perfectly flat, and perpendicular to the back surface--the one that sits against the mold--which is also perfectly flat (the fit between these two surfaces needs to be very close).  Once the oversize block's been fitted, you can use templates derived from your drawing to lay out the shape of the block, and then go to the band saw to cut away the excess. 
And there's the result.  Now we've got a lute-mold-in-the-making that looks a little less like a battleship, but a little more like a duck-billed platypus.  Still, it's progress, and a little progress every day is all I need to keep me coming back for more.

Next time we'll start refining the shape, and laying out rib lines.  Hope to talk to you again soon.