Thursday, October 8, 2015

Greenish Luthiery

My first shop-made finger planes, 8mm wide iron, 60 degree body in back, 40 degree body in front with maple shavings.

I have a new obsession. I'm familiar with the feeling of obsession settling around my shoulders. That's how I got started working with hand tools.

Back in August, someone posted a link in the Facebook Unplugged Woodworkers group to this video of Dominique Nicosia making a violin by hand. He's a master instructor at the Ecole Nationale de Lutherie de Mirecourt (National School Of Luthiery of Mirecourt, France). It's a beautiful documentary of a fascinating process. I was absolutely enthralled and inspired.

I watched it a second time, and thinking about the set of videos I had recently put together for my Intro To Hand Tools course, I realized that except for a few specialized tools and procedures, I knew how to do everything he was doing. I could do this!

That was the moment I felt the obsession take hold. Over the past two months, I've watched several dozen other violin-making videos and read 5 books on the subject. The videos range from short summaries to whole multi-part series detailing the process from start to finish. The books range from the late 1800's to the modern day. I've started lurking on several luthiery forums and attended a meeting of the Guild Of New Hampshire Woodworkers' Granite State Luthiers group.

In the shop, I've made several specialty tools, refined my carving gouge sharpening skills, and practiced the procedures for gluing up a bookmatched body plate and bending rib pieces.

Of course, this has all been hobby pace, a few hours at a time, plus reading on the train to and from work. It will supply an abundance of future blog posts. This is just a summary of what I've learned and done so far.


Luthiery requires several tools that I didn't already have, some general-purpose, some very specialized. Specifically, glue pot for hot hide glue, bending iron, finger planes, purfling tools (purfling is the inlay around the edge of the body plates), carving knives, reamers, and peg shapers. That comes to over $600.

Since we're currently being ground into the dirt by the oppressive boot heels of college costs, I've tried to improvise as much as I could. I've managed to assemble a reasonable set of shop-made tools for under $100.

For the glue pot, I went with the universal cheap solution and got a hot plate and pot. I boil the glue in a glass jar.

For the bending iron, I mounted a piece of 1" aluminum tubing to a 2x4 with a metal gate handle and pipe clamps. I found that  3/4" copper pipe fits in it nicely to add thermal mass. I heat this with a propane torch, or where open flame isn't practical, a 3/4" curling iron stuck inside.

Torch-heated bending iron, with a bent practice rib and the raw billet it was sawn from.

I made a couple of wooden finger planes based on a photo essay by Mario Proulx in the Musical Instrument Makers Forum Library. I made irons for them by cutting up an old, mostly used up bench plane iron with a hacksaw and file.

The purfling gauge is a specialized cutting-style marking gauge. One of the books has an illustration of one I can make. I can make a purfling chisel (for picking out the waste between the cut lines) from an old allen wrench.

For carving knives, I'll use my chip-carving and pocket knives. I may try making a simple violin-making blade from an old plane iron, experimenting with some backyard heat-treating.

The irons I've cut up so far have only been hardened on the cutting end, from the edge up to the chipbreaker slot. The remaining metal is soft, surprisingly easy to hacksaw, about like handsawing 3/4" hardwood. To cut the hardened portion, I score a line with the corner of a file, then grip the piece with vise-grips and work it back and forth gently until it comes off through metal fatigue.

Old plane iron cut up to make 3 finger plane irons in 8, 10, and 12mm widths.

For the reamers, I'm going to try a version of Drew Langsner's chairmaking reamer. I should be able to make up a peg shaper from an old plane iron.

One additional item I've made is a veneering saw for sawing out the 1mm rib stock. This is similar to a kerfing plane, but setup specifically to cut rib stock to its 1.5mm rough thickness. I remove the last half mm with cabinet and card scrapers. Being able to precisely resaw close to final thickness is a significant timesaver.

I may also rig up a toothing gauge for breaking up the surface prior to scraping. This is based on a description of a tool called a filliere, a veneer thicknessing gauge, though I haven't been able to find a picture of one. Lie-Nielsen makes a similar tool for precisely thicknessing narrower pieces, a stringing gauge.


Initially I was wondering what to do about materials. My first plan was to buy some inexpensive beginner's top and body blanks. These are quartersawn segments of log cuts.

I recalled watching Peter Follansbee plane green oak log splits into boards for his carved wooden boxes. If only I had some logs I could use for my own blanks using the green woodworking techniques I had learned from Peter and his teachers, Drew Langsner and Jenny Alexander.

Then I realized that I did have some. Back in 2006 when I had first started learning green woodworking, the brother of one of my coworkers had a good size walnut tree come down in his yard. I bartered some oak log lengths I had been collecting and riving for a 4' clear section of the trunk, about 20" in diameter.

I had left this log in my yard for several years, not really treating it properly as I tried to decide what to do with it, then finally quartered it with wedge and sledge. The quarters have been sitting in the corner of my workshop now for about 5 years. They're cracked and checked considerably due to poor storage, but there's still plenty of usable wood.

This walnut will make an excellent supply of practice material. And I don't have to discard the practice pieces. I can make decorative boxes using luthiery techniques as I refine my skills. After all, a violin body is simply a box with curved top and bottom; use a flat bottom instead and you have a lovely delicate box. It doesn't have to produce sound. That will come later.

I also have a small supply of yard maples that I've collected from people, quartered, stacked, and stickered. Most of it is in firewood lengths, because that's what people do when they're cleaning up fallen trees, but that's just fine for this work. All of the wood is nice and dry, seasoned in my basement for the past 5 to 7 years.

The traditional woods for a violin body are spruce for the front (the top plate), and maple for the sides and back (ribs and bottom plate), all quartersawn. Walnut is somewhere in between, closer to the spruce in hardness than to the maple. It's a very workable and beautiful wood. The traditional woods for the neck and fittings are maple and ebony.

The Process

The process for making body plates is to join two quartersawn wedges at the bark side (i.e. the thicker outer edge of the wedge) in a bookmatch, after having planed the edge square to one flattened face. So the two wedges are glued back to back.

This forms a plate, flat on one side, with a thick center and thin edges. The plate will be arched, shaped and hollowed to a thin shell curved in length and width. This forms the graceful outer surface and hollow body. The centerline joint is the apex of the arch.

The outside arching process is one of carving to convex curves. The inside arching process is one of excavating to concave curves. The result is a thin shell just a few millimeters thick, carefully contoured and smoothed.

The ribs, just 1mm thick, are shaped on a hot bending iron and glued up to blocks on a body mold. The plates are glued to the ribs, separating them to produce the sound cavity. The carved neck is joined to the body with a glued dovetail joint.

The glue is hot hide glue. This is reversible, so the body can be opened up for repairs. The finish is varnish.

Over the centuries, many old violins have had their necks replaced to adapt them to the new, higher modern concert pitch (modern as of, say, 1800). Beyond that, the design hasn't changed in 500 years.

The bare violin is then fitted up with pegs, fingerboard, bridge, and tailpiece. Only the fingerboard is glued in place. The strings are fitted to the tail, run across the bridge, down the length of the fingerboard on the neck, across the nut, and wound on the pegs.

As they are tautened and tuned to pitch they exert pressure through the bridge onto the top plate. Inside the body, the bass bar reinforces the top plate under the bass foot of the bridge. A loose dowel (the post) is wedged between top and bottom plates under the treble foot.

The science of violin acoustics is amazingly complex. However, the basic mechanics are straightforward. The horsehair in the bow actually has a microscopically toothed surface. Bowing this over the strings makes them vibrate. The bridge transmits these vibrations to the top plate, while the post and ribs transmit the vibrations to the bottom plate. All of this sets the air in the cavity vibrating, moving through the "f" holes.

As with any other woodworking endeavor, there are multiple ways to build a violin. The sources I'm using cover a range of hand and power tool techniques, different order of operations, and different types of inside and outside molds.

This is why I like to learn from multiple teachers. Each one has a different perspective and process, emphasizing different details. By themselves, no single reference quite captures everything, but the aggregate knowledge across all of them covers it well.

Practice Plates

Step one of making a body plate is to cut down a tree, section it into manageable lengths, then quarter it with wedge and sledge and season it for 5-10 years.

However, you can speed up this step by ordering seasoned, quartersawn body stock from a luthiery supplier. They sell it in a range of quality levels from beginner to masterpiece. Start with the cheap stuff.

I call this "greenish" luthiery because I'm using green woodworking techniques, but the wood is seasoned. I used a froe and wooden maul to rive a quarter into eighths, then sixteenths. I used a drawknife and heavily cambered jack plane to remove the sapwood from two splits.

Walnut log wedge riven out with froe and maul.

Planing a rough split requires special workholding, since neither side is flat, and the surface to be planed is at angle. The clamping method I used is something Paul Sellers showed me. It works very well for awkward shapes.

Holding the rough wedge for planing. There's a scrap underneath to support the thin side and bring the top approximately level.

Once I had planed a reference face, I planed the wide edge roughly square to it. The shape was still a little awkward, but it mounted edge-up easily in my face vise. If necessary, a wedge-shaped spacer can be used to help steady it.

For the final precision squaring of the edge, I used my large edge-shooting board. This is the method luthiers use for planing bookmatched guitar bodies. With flat pieces, you can fold them back and plane the matching edge of both pieces together. However, with these wedges you have to do them individually.

A good rub joint requires edges as perfectly planed as you can manage. You should be able to hold the pieces together on their planed edges up to the light and not see any pass through the joint.

Test the joint by rubbing the two pieces together along it and pivoting them back and forth. There should be no high, low, or twisted spots. Anything less compromises the integrity of the joint, and it may come apart during construction or when tightening up the strings.

I mounted one piece edge up in the vise, spread glue along the edge with a brush, and set the other piece on it. I rubbed it back and forth to remove any air bubbles and spread the glue uniformly. It started to set up quickly. This was the first time I had ever used hide glue, so I wasn't entirely sure I had the viscosity or temperature right. Another reason to practice!

I drove small pinch dogs into each end of the joint and set it aside to cure. It's now ready for practice shaping.

The glued up plate (secured with pinch dogs) and practice rib on my large edge-shooting board.

Practice Ribs

I planed an additional walnut 1/8th wedge into a rough billet, then tried several methods for resawing quartersawn rib pieces.

The main challenge is that they are so thin. The finished thickness is 1mm, so I tried to resaw around 2mm to minimize the subsequent planing and scraping required. With such thin material, one errant twist of the saw easily cracks it off. That made a full-size rip saw a littly tricky to handle.

A ryoba, a Japanese pull-saw with thin blade and no set to the teeth, worked well. I tried sawing completely through, and starting fresh from each side. This required close attention to maintain proper thickness. An error of just one thickness of the saw was a good 10% of the final thickness!

Next I tried creating a starter kerf on each side with a 10ppi joinery backsaw for better thickness control. This worked well enough that I tried a deeper kerf, leaving just a little to finish off with the ryoba.

That led to the idea of making a stepped guide fence that I could clamp to the backsaw to precisely space the kerf and maintain it flat to the face. The only problem with that was the backsaw teeth were too fine, taking too long.

The final iteration of all this was to clean up a rusty flea market 7ppi ripsaw, sharpen it, then cut it down to avoid the twist off problem I had with the full length saw, and secure the guide fence to it.

The veneering saw with guide attachment and a couple of bent practice ribs. I'll drill and bolt the guide piece with wing nuts so I can remove it for sharpening. The saw plate cutoff will make some nice scrapers.

The veneering saw in action. In the background you can see my fancy hot glue setup.

The end result was a fast, repeatable method for cutting ribs close to final thickness. I clamped one end of the rib to the benchtop and scraped it down to final thickness with a cabinet scraper and a card scraper.

Scraping a rib to final thickness.

Closeup of the shavings produced by the cabinet scraper and card scraper (thanks to Phil Lowe for the cabinet scraper sharpening technique and GNHW cofounder Terry Moore for the card scraper sharpening technique!).

You can also use a bench plane or block plane, but planing thin stuff like this can be tricky. I found that well-tuned scrapers did an excellent job with lots of control. I could easily scrape down any high spots.

The torch-heated pipe made a good bending iron. I could quickly heat it to the point that water droplets would skitter around on it, then turn the torch to minimum to maintain the temperature. Of course you have to be careful using this setup to avoid burning yourself or starting a fire.

A 3/4" curling iron stuck in the tube didn't get quite as hot, but was still reasonably effective. I may see if I can find a different iron capable of higher temperature. People have also tried soldering irons and various heating elements in pipes, such as water heater elements and electric charcoal starters.

One of the keys to bending without cracking is to back the piece with a metal bending strap. I bought a small roll of aluminum flashing and cut out a strap about 10" long by 2 1/2" wide. The strap applies the bending force across the surface of the wood as you rub the moistened piece back and forth on the iron.

The walnut bent easily and quickly. The hot iron heats the lignin in the wood to a pliable state, which then cools to hold the formed shape. Moistening the surface helps spread the heat; it's not quite steaming the wood.

Using the various rib pieces I had prepared, I bent loose and tight curves. The curved rib sections are called bouts. The center bout is called the C bout, because it's in the shape of a letter C. This has the tightest curves, at the curled ends.

Next Steps

Next I'll shape the top plate I've glued up, and make up some more plates and ribs to refine my process. Then I'll try inlaying some purling. I'll use all these pieces to make up some nice gift boxes.