Building a Cello–Step #4: Bending and Installing Cello ribs the traditional way.

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Step #4–Bending and Installing cello Ribs

Bending iron, bending strap, clamping caul, International Violin Co.

Proper tools

The best tool for this job is the traditional bending iron. You could make one that would be quite functional, for very little cash outlay, but the nice thing about the “traditional” ones, available at International Violin Co. and many other sources, is the variation of curves available. The Iron (by the way, they are no longer made of iron, but aluminum…the name has stuck, though) is “egg-shaped”, and on the small end has a tight enough curve to form the tight bends at the corner blocks, but at the center, it is flat enough to gently curve the portions of the ribs where they span the lower bouts of a large instrument such as a cello. 

Bending a cello rib
This is how a Bending Iron is used to bend a Cello rib to the correct shape.

The Bending Iron MUST be hot!

The key to successful rib-bending is that you MUST get the wood hot all the way through before commencing the bend. If you don’t do this, you can almost guarantee you will break the rib. How hot? Good question.

I used to use a clothes-iron, and wooden molds, around which I would bend my ribs. The clothes iron was rigidly fixed in position so that the hot side was up, and the thermostat control was set on “linen”. At that temperature, if you are not careful, you can scorch the wood. At that temperature, also, if you dribble water on the iron, it dances, and bounces as it boils away to nothing. It can’t just sit there and steam. So that is my test on the bending iron as well. I want the water to dance and boil instantly, not just sit there and simmer. On the commercial bending iron, it takes 20 minutes or so to get hot enough…maybe longer. Be patient: this is critical. The iron has to be hot.

 

Step 2 bending the rib
The bend has to be gradual, with constant, firm pressure on the bending strap.

Bending Strap

The bending strap can be bought, but, if you can secure a thin strip of aluminum (aluminum roll roof-flashing is almost too thick, but it will work) you can affix handles of wood, and it will be fine. For violins, I cut up one of those large beverage cans, in a spiral (as a cardboard tube is made) , to produce a strip about 40mm wide, and long enough for a bending strap.

The bending strap accomplishes several things. The most important, in my mind, is that it supports the outside of the curve and prevents the wood from “stress-relieving” through fracture. Especially in heavily figured woods, it is very common for an unsupported rib to break along the curl. (Rats! Your beautiful rib just became beautiful firewood!) The second thing is that it allows you to put pressure on the whole part of the rib being bent, as it gets hot enough to really hurt you if you touch it, without endangering your fingers. It is a good idea to put handles on the bending strap. (By the way, some people use cloth, instead of metal, for their bending straps. Brass or aluminum are the most common metals used, though.) Metal transfers heat pretty rapidly, so wooden handles are very helpful. Thin gloves aren’t a bad idea either, but I usually think of that after I am well into the bending process and it is too late to stop and put them on.

 

Spritzing a rib-blank with water before bending
You don’t want the rib saturated with water…that will result in a broken rib–just spray it all over, quickly, and immediately begin heating it for bending.

How Much Water?

Some folks bend their wood dry. Some soak their wood. I use just enough water to get the wood wet on the outside (spray it on; no soaking) and enough to produce a little steam while I am heating the wood. I want it completely dry when I remove it from the heat.

Bending the Ribs

Method

Press the wood against the flatter porton of the iron while it is heating (count off at least ten seconds), then slide it toward the end with the curve that most closely approximates the bend you need, and slowly, firmly press the wood into shape with the bending strap against the bending iron. Hold it another ten seconds or so, and then let off a little, to see if it will hold that curve. If it springs back, pull it tight again, and hold it some more. Pay attention to smells, at this point. It will smell like something baking in an oven. You do not want to scorch the wood. (Try this with wood you can afford to lose, a few times, before using the nice expensive rib-stock you bought.) I broke and/or burnt a number of ribs, trying to learn this skill. But I know a guy who uses an old piston from a diesel engine for his bending iron, and heats it with a propane torch. Others have used water pipes, curling irons, charcoal briquette lighters and the like. I finally got a “real” bending iron after I had made 15 instruments.

Specific to cellos: I made my thickness 2mm, and used a large bending strap, as shown. While you can’t see the mold in the photos (I forgot about the camera until the real cello ribs were done and installed) what I did was to set the cello mold nearby, and bend a rib, then check the bend against the actual mold, to see if it was close to correct. Then, back to the bending iron, to correct it. When a rib was satisfactory, I immediately clamped it in the mold, to hold that curve while it cooled. Once it was cool, it would hold that curve permanently.

Sequence

The reason we do the inner c-bout ribs first is that there is frequently a fair amount of pressure put on the ribs during the gluing/clamping process, and if the corner blocks were cut to their final shape, they could flex, and permanently change the shape of our corners.

After the c-bout ribs are glued with hot hide glue, and thoroughly dried, I shape the outer sides of the corner blocks. The black lines you can see below are ink, where I accidentally allowed the template to move as I was marking the corner blocks. Those marks were removed when I leveled the garland, which we will talk about in a later article. The curve of the outer side of the blocks is extended through the C-bout rib, so that the upper and lower ribs overlap the C-bout ribs.

Clamping the ribs
This is how the bent ribs are fitted into the mold and glued to the blocks.

Clamping and gluing

I cut clamping “cauls” (curved wooden blocks) to help hold the ribs tightly to the blocks while gluing. The holes in the mold are positioned in such a way that the clamps will be pointed the right direction to achieve maximum hold while gluing. Do four or five “dry-runs” before actually applying the hot glue. In fact, it is a really good idea to have things clamped in place, and just remove the clamps on one end long enough to apply the hot hide glue and re-clamp immediately. Clean up around the joint, immediately, with hot water and a rag or brush. Let the glue dry overnight. If you have to re-work a joint, a teakettle’s steam, as close as possible to the spout, will unglue a joint in about 20 seconds. Watch the fingers. Steam is hot. (Close to the spout, where the steam is invisible, is where you want to be.) You can get a serious burn if you are careless.

I use a $3 “potpourri heater” from the Goodwill store for my glue heater. I put an old yeast jar in it, and fill with water around the jar. I keep the lid on the jar when I am not actively using the glue, to keep it from drying out. It seems to work pretty well. I am told that 145 degrees F. is the correct temperature for hide glue. You can get good glue from a variety of places. I’ll talk more about glue, and the glue-pot, in a later article.

After the glue is completely dry, I cut off the excess upper and lower ribs at a right angle, exactly at their intersection with the C-bout ribs, so that the glue lines follow the inside corners of the upper and lower rib ends, and are essentially invisible.  (I do NOT “miter” these corners–I hide the joints by putting them right on the corners of the squared-off ribs.)

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Building a Cello–Step #3: Building a collapsible mold with which to build a cello.

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Step #3 Making the Mold:

Interior mold

Cheap, plywood, collapsible mold

The mold is a structure to hold the shape of the ribs until they are glued to the front and back plates, as well as to hold the blocks rigidly until the corpus is assembled. Since the plates actually derive their respective shapes from that of the mold and ribs, it is very important to get the mold as accurate as possible.

Planning Block attachment–and removal

In small molds (violin, viola, etc.) the end and corner blocks are simply glued into the mold, and the glue line is broken later, in order to remove the mold from the body of the violin or viola. (Remember that the blocks are a permanent part of the instrument– the mold is temporary. It has to be right, but it can be “cheaply right”, or “expensively right”. I went with “cheaply right”.)  In larger instruments it is possible to secure the blocks using screws from the inside of the mold, so that it is not necessary to break glued joints in order to remove the mold.

Collapsible Molds

Furthermore, it is desirable to be able to remove the mold piecemeal, so as to not stress the rib structure trying to pry the mold out. (I have broken more than one rib, trying just a little too vigorously to remove the interior mold.)

 

Cello mold parts
This mold is designed to come out in pieces, for easy removal.

As you can see, above, the main body shape was simply built up with layers of plywood. I had a bunch of scrap plywood in my shop, so I traced out individual sections, from the mold template (from step #2), cut them all out, stacked them, and secured them with glue and drywall screws.

What you may not be able to tell is that the left and right sides of the main part of the mold can be released from the center blocks on each end, to facilitate mold removal. They are not glued there– just held with screws. The front and back sections are one-piece each, but are easily removed before the linings are installed. (The linings are what makes mold-removal tricky. We will talk about linings later on.)

So, essentially, the whole mold is in six pieces: left and right, top and bottom end blocks, and front and back sections. After they were all assembled, with extra room left around all edges, I checked one last time, using the mold template, and cut the mold out on a bandsaw, then smoothed the sides on an oscillating spindle sander (like a drum-sander). The sander keeps the edges at a right angle to the front and back. It is really a handy tool, which has paid for itself many times over.

 

Partially assembled cello mold.
Here, the front of the cello mold is in place, but the back is still off.

Above, you can see that the front and back sections of the mold are secured only with screws, so they can be easily removed, after the ribs are in place, so the linings can be installed. I used about eight screws each, front and back.

 

Mold construction detail.
Cello mold with end block screwed in place for easy removal.

Here you can see how the deck screws pass through the end block of the mold, to secure the end block of the cello. You must be sure to use short enough screws that they will not protrude all the way through the block. You only want the screws to penetrate the blocks by 3/4″ or so, and right along the center line. If you ever run into one of those screws with a cutting tool, you will be shocked at the damage it will do to your expensive tool. Notice that in this photo, the blocks are already shaped. In reality, they are installed in rectangular form, and shaped afterward. See the next picture.

Tracing the Template shape onto the Blocks

Tracing block shapes from mold template
This is how the block shapes are transferred from the mold template.

This is how the mold template is used to trace the shape of all six blocks. You trace one half, then flip the template over to trace the other half. Be very careful to do this step accurately, as it will determine the final shape of the cello.

Shaping the Blocks

I cut the inner curve of the center corner blocks close to the line with a bandsaw, then used the spindle sander again to get exactly to my line. I wait until after the C-bout ribs are installed to trim the outer part of the center blocks. I’ve never had a block fail, but I have been told that if you cut them too soon they can be fragile and flexible, and you may end up either bending or breaking them.

Next we’ll talk about bending ribs.

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Building a Cello–Step #2: Making cello templates for molds, scroll, and arching

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Step #2–Making Templates

Mold template, scroll template, arching template

How do I transfer those lines?

Having chosen to use the 1712 Davidov Stradivarius cello as my pattern, I went to a copy shop, and had them make a photocopy of the drawing on the back of the poster. They made three copies, as I intended to cut the copies up in making the templates. I pasted the cut up photocopies to thin plywood (“door-skin”), and then cut out the shapes seen in the photos below. An even better material for templates, produced in exactly the same way, is 1.5mm Aluminum.

Still another way, which I use on smaller instruments, is to use clear, 3mm plastic (lucite, plexiglas, whatever you call it) and trace with a scribe, directly over the original drawing. The resulting template is accurate, transparent, and does not warp with a change in humidity. Your choice…

How Templates are used:

The idea behind the templates is that I should have a flat pattern to trace around when determining the shape of the mold and a curve to match the shape of the archings as I carve the topography of the plates. Photos below: Continue reading “Building a Cello–Step #2: Making cello templates for molds, scroll, and arching”

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Building a Cello–Step #1: Pick a pattern! What kind of cello do you hope to build?

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Step #1– Choosing a Model

Ruggieri, Montagnana, Stradivari, Amati, Maggini, Guarneri, Gofriller, Gasparo da Salo, Strobel, etc.

What Cello should I build?

There are almost as many different models of cello as there are of violins. Stradivari made them, as, apparently, did Giuseppe Guarneri, as well as those before and after them. Both Andreas Amati and his illustrious grandson, Nicolo Amati, made celli. Franscesco Ruggieri, Andrea Guarneri, Gasparo da Salo, Giovanni Maggini, Matteo Gofriller, and Domenico Montagnana are other makers famous for celli. But I really was going to choose between only three possibilities:

1. Someone had given me a plan for the Montagnana “Sleeping Beauty”, which has a good reputation for a big sound.

2. There are two complete sets of plans in Henry Strobel’s book, Cello-Making, Step-by-Step–one a full-size model, and the other a 7/8 size.

3. I had bought a poster from The Strad Magazine, with a detailed drawing of the 1712 Stradivarius known as  The Davidov.

The Davidov was being played by Yo Yo Ma, a world-class cellist. I really liked the looks of it (the Sleeping beauty is kinda chunky), and it is a known entity (those in Henry Strobel’s book are lesser known). So, with all that (and the fact that Paul Schuback assured me it was a good choice) I settled on the Davidov. Nothing arcane about it– I just grabbed the one I liked, really.

One thing that had been a vote in favor of Henry Strobel’s plans is that the plans were already drawn, including the lines for the mold. The poster gave all the information for the original instrument, but I had to come up with the mold template myself. That was OK, but I ended up a few millimeters oversize. My fault.

Photo-Essay of my first cello-build

In case anyone wants to see this whole series at once, here is a link to the original blow-by-blow photo-essay on Maestronet. It took 13 weeks of spare time work from start to finish–between 250 and 300 hours, I would guess.

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Annnd… I’m Back. With a New Fiddle.

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Resurrected Website: Bluefiddle’s West Wind Strings

A couple of months ago, in my befuddled, well-meaning, bungling way, I killed my website entirely.

The host was able to save it, but I had been in the process of changing hosts, so that was a bit awkward. I have switched from Joomla, which I was just beginning to understand to WordPress, regarding which I understand nothing…and have bought the requisite book: “The Complete Idiot’s Guide…”  Sounds as though it was written for my kinda guy. A friend has reconstructed the site using WordPress, and has assured me that I will be able to master the new software.  I trust he is correct.

New Five-string fiddle

I did complete one new instrument since I last posted: a five-string fiddle (sometimes called a “bluegrass fiddle”), using the wood from the Big Leaf maple log I had been given a few years ago. This is the first instrument I have made using that wood, and I am delighted with the look, response and sound. Here are a few photos of the new, handmade in Oregon, bluegrass fiddle:

Continue reading “Annnd… I’m Back. With a New Fiddle.”

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