Two Bass Bars

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Two Bass Bars

How I install bass bars:

The bass bar in a violin-family instrument serves to support the bass-foot of the bridge, and the bass-side of the front plate (also called the “table” or, the “soundboard.”) Without adequate support in the proper place anong that side, the bass tones will sound quite flabby and unconvincing. The following is only a description of how I install the bass-bar, not telling anyone else how it ought to be done.

We always make the bass bar of European spruce, with the grain vertical to the plate; thus, flat-sawn to the bass-bar, itself. I begin by laying out two locations, one seventh of the distance from the center seam to the widest part of the bass-side edge at both upper and lower bout. That usually translates into about 15 mm off the center, at the widest point of the lower bout and 12 mm off center for the same place in the upper bout. I strike a line through those points , checking to see if it is far enough away from the inner eye of the bass-side f-hole to actually accommodate the completed bass-bar If it is not, then I move the line over a couple of millimeters, as needed, to gain clearance at the f-hole. Then I measure 40 mm inboard along the line from the upper and lower edges of the plate, to designate the end locations for the bass bar.

I cut the bass-bar blank to length, and plane it to the appropriate thickness, then hold it on the lines I have laid out, essentially perpendicular to what will be the plane of the ribs. I use a compass, set to the maximum gap at the bottom center of the bassbar, to scribe the contour of the plate onto each side of the bass bar. (Notice that, due to the compound curves of the violin plate, the two marks will not be the same. This is important.) Once I have both sides traced in accurately, I carve away the excess wood outside the line, to follow the line as closely as I can manage. I try to achieve a straight line between the two, regardless of where the two lines go, because that will follow the complex curves of the plate.

I double-check the bass-bar against the plate, and usually it is surprisingly close to fitting, at this point. So I use a strip of the paper-gauze tape available in pharmacies, about an inch wide, to cover the layout lines I had scribed into the plate, and then proceed to chalk-fit the bass-bar on top of that tape. The tape is very thin, so that I can see the lines through it (although I do trace them again onto the tape, to make them even easier to see.) But the tape is also so thin that, if I can get a perfect fit on the tape, when I remove the tape, I will have a perfect fit on the plate, as well, and no chalk residue to remove.

The hardest thing for me to learn in chalk-fitting, was to only remove the transferred chalk and the wood immediately under it, not the whole area. Frequently the culprit in an imperfect fit is actually quite a small area, so it is counter-productive to remove too much wood.

I chalk the tape, along the layout lines, and then press the bar into place, sliding it lengthwise a few milimeters back and forth to pick up some chalk;. I plane or scrape off the high spots where the chalk transferred, then try again. When I get a more or less full transfer of chalk from tape to bass-bar, I know the fit is acceptable. Then I carefully remove the tape, and (finally) glue and clamp the bar into place. Usually, I trim the bar a little, first, so it is nearly the correct shape on the top surface, so the clamps will fit more easily.

One bass bar is complete: the other has only been trimmed to make it easier to clamp.

After the glue has dried and the bar is rigidly secured, I use finger-planes to trim the bar to the size and shape I want.

Beginning with a medium-sized finger-plane.

Final touch-up with small plane and scrapers. The camera angle is what is making the two bars look so different.

Installing the top plates

So, the next task is to complete the inner edgework, and then install the top plates on the rib garlands. I plane a tiny bevel around the edge of the plate that will face the ribs; then file it to a curve, nearly quarter-round, flush with the outer rim of the plates. Then I position the plate on the garland as precisely as possible (sometimes things seem to have moved a bit, so I have to compromise a little.) Finally, I loosen a few of the spool clamps at a time and slip hot hide glue into the joint, using a thin palette knife. I clean up all around, so as to not leave glue on the outside of the violin.

Spool-clamps. — Spool clamps can look like these, or even more simple: sections of closet rod with all-thread bolts. There are a lot of possible options.

Finally, the plate is fully glued and clamped, and I wait for it to dry.

Guarneri copy top plate installed with hot hide glue and spool clamps.

After the top plates are installed, I trace the European Maple back plates and cut them out. Here are the two garlands with the top plates installed and the back plates cut out:

Next stop will be arching the back plates.

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February 13, 2018February 13, 2018

Closure!

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Closure!

Leveling the Garland

Last time I posted, I had installed the back linings, shaped the blocks and linings, and was nearly ready to close the box. It looked like this:

The blocks and linings are shaped. — The blocks and linings are shaped…but the garland is not leveled, yet.

To the unassisted eye, the back of the garland really looked pretty flat. In fact, I had used a hand-operated abrasive tool (a Sandvik tool…they apparently went out of production, years ago…but I love the few I have) to try to level it all the way around, thinking it might be easier. But when I clamped it up, to test the plan, it was not even close to level…so, back to the sanding board!

To level the garland, I made pencil marks all around the mating surface of the garland, and then rubbed the entire structure on the abrasive surface until all the marks disappeared. Presto! Flat!

Installing the Back Plate

Then, while the glue was heating up, I carefully went over the perimeter and inner surface of the back plate and made sure the curves were smooth and consistent. Once I was satisfied with it, I carefully aligned the back plate on the garland, pushing and pulling a little to get the overhang even, all the way around. I clamped only at the blocks, initially, then began using a thin-bladed palette knife to insert glue into the joint. I removed the clamps at the bottom block, first, and inserted glue so that the joint between the bottom block and the back plate was fully coated, then slid the blade left and right, as far as it would go, spreading glue on the joints between ribs/linings and back plate. I quickly reapplied the clamps at the bottom block, and added more between there and the corners. Loosened the next set of clamps, and repeated the routine.

Once the entire perimeter was glued and clamped, with an extra clamp at the button-to-heel joint, I could set the whole assembly aside to dry. It is closed! (I really like looking at that one-piece European maple back.) 🙂

Closed Corpus, Front view. — Closed corpus, front view.

I will let the glue dry overnight, then remove the clamps and trim the heel to the correct profile, trimming button to match the heel, so that they are shaped as one unit. Then I will carve the slot in the back plate for purfling, install the purfling, and, finally, prepare the whole instrument for varnishing. I hope to be ready to begin the finishing process by this weekend.

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January 22, 2018January 22, 2018

The Plates

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The Plates

Shaping the linings

Last time, I had the Garland complete, except for trimming (shaping) the linings, and levelling the front of the garland so I could trace the shape of the plates from the completed garland. I shaped the linings, using a small sharp knife and a scraper:

Shaped linings — The linings are shaped using a small sharp knife to cut the taper, and then scraped smooth, using a scraper.

Leveling the Garland and Tracing the Plates

I leveled the garland by rubbing it on a sanding board (coarse abrasive cloth glued to a flat aluminum plate, in this case), and then used a washer to trace the shape onto the front plate. The washer adds 3 millimeters around the perimeter of the garland, to allow for the plate overhang on the finished instrument. I still have to shape the corners separately, as the washer simply makes them round:

Tracing the plate perimeter, using a washer and a ball-point pen.

The Front plate perimeter as initially traced: notice the round corners. — The front plate perimeter as it was initially traced: notice the round corners.

Corrected corner shapes. — Now the corners have been refined and corrected. I am deliberately leaving them on the long side; I will trim them later.

Cutting out the Plates

I used a bandsaw to cut out the plates, as close to the lines as I could, without touching them. Then I used a spindle sander to bring the perimeter exactly to the lines, and, finally, I used files to smooth out any ripples left by the sander. I am really not comfortable looking at these extra-long corners, but, once the garland is glued to the plate, it is very easy to trim them to the exact length I want; and much more difficult to put wood back, if I remove too much.

Front plate cut out. — Front plate interior, cut, refined, and ready for carving. The lines show the margins, and the corner and end-blocks’ shapes.

I am deliberately leaving my corners abnormally long, as one of the problems noted by my teacher is that I have had a pattern of making rather short corners. (Ironically, I had only done so as an over-correction to an early tendency to make my corners too long. Sigh…)

I handled the back plate in similar fashion to the front, and completed it next. It was very important that I remember to trace the front plate off the front of the garland, and the back plate off the back. The two look very similar, and will match very well when complete, but they are not precisely symmetrical about the centerline, so; if I forget and trace them both from the same side, then one of them will definitely not fit. (Ask me how I know….)

Now I am ready to begin plate-carving. I will begin with the front plate, simply because it is easier on my hands. Furthermore, the pattern of building I follow requires that the front plate be completed first anyway. But, honestly, the older I get, the more it stresses my hands to carve the maple, so it is nice to have the front plate completely done, and to feel good about that while I begin to tackle the back plate.

Both plates, along with the completed garland. Looking at the interior of each plate, and the front side of the garland.

To you sharp-eyed observers, the reason the slant of the “flame” on the back is going up from left to right, instead of down from left to right, is that you are looking at the inside of the plate. When I turn it over and carve the outside, you will see that it slopes the same way as the one in the poster.

Over the next few days, I will move toward completing the carving of the front plate. Then…well, you can follow along and see. 🙂

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September 9, 2015September 10, 2015

5-String Progress #9: Back Plate

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Five String Fiddle Progress: Back Plate

Flattening the back of the garland

After the glue was completely dry, I removed all the clamps from the linings and cleaned up the interior: that is to say, I tapered the back linings, so that they faired smoothly into the ribs, and I shaved and scraped the blocks to their final shape.

Then I rubbed the back surface of the garland (rib and block structure) on a “sanding-board” to level the back of the garland, and to ensure that the back of the neck heel was completely level with the back of the garland. That way, I can fit the back plate absolutely flat against the garland, and trace the shape.

I didn’t take a picture of this procedure, this time. Here are some taken when I was building a cello:

Flattening a cello garland on a sanding board.

I make pencil-marks on the edges of the linings, ribs and blocks, all around, and scrub until the marks disappear. When all the marks are gone, the garland is flat. It gets pretty vigorous and physical, but it is quite effective.

Here is the flattened garland, ready to trace the back plate:

As you can see, the blocks are quite smooth, now, and the linings taper gently into the ribs. After this point, there will be no more changes to the interior of the corpus, except as it directly affects the back plate.

Tracing the plate

I clamped the plate to the corpus, carefully centering the glue-seam of the back plate on the centerline of the neck and the end block.

Garland centered on plate — Garland centered on the back plate

Then I traced around the garland using a ball-point pen and a flat washer whose flange is exactly 2.5 mm wide, so that my line will be 3 mm from the ribs, all around. I watch carefully to make sure the washer stays flat on the plate…they have a tendency to flip up and follow the pen. I work along the perimeter, giving several strokes to every part, so that the line will be visible against the dark wood. Notice that this procedure makes “round” corners. I will modify them before cutting them out, so that they are the correct shape.

Tracing the shape of the plate. — Tracing the shape of the plate, using a washer and a pen. (Yep, that is a Gunderson pen!)

And, there is the plate, almost ready to be cut out:

Traced plate, ready for cutting out. — Traced plate, almost ready for cutting out.

One thing I do, that I forgot to photograph, is that I re-shape the corners. I use a straight-edge to connect a line from the end of the rounded corner where the pen circumscribed the corner of the rib to the center glue line at the location where the purfling will cross the far end of the plate. (Or, you can just use a 30/60/90 triangle to lay out a 30-degree angle off the center glue line on the end of each corner. But I do it with the straight-edge.) Then I continue the curves of the inner bouts to connect with the straight lines I just scribed in, and the corners are complete. I use a sharp scraper to remove any ink lines that are not part of the perimeter outline, and then I really am ready to cut out the plate.

Cutting out the plate

I use a band-saw to cut within a millimeter of the line, and then use an oscillating spindle sander to perfect the edge, right up to the lines. These and my drill press are pretty much the only power tools I use, though I have occasionally used an angle-grinder with a coarse sanding disc to remove rough excess wood, on larger instruments.

I run my fingers around the edges looking for lumps, and work those out as well, using a file as needed. Here is the completed plate blank:

At this point I also sketch in the interior graduation plan–just the outline of the inside boundaries of the plate, so that I know where I am going to carve. There is no reason it has to be done at this point, but it helps me remember which side was outside and which inside…and that really does matter, as the plates are vitually never exactly bilaterally symmetrical. If I forgot and arched the wrong side, the completed plate would never fit the garland (ask me how I know…).

Interior Graduation boundaries sketched on correct side.

You can see that there are numerous bark inclusions in the wood, which I will fill with matching wood…but I will wait until the arching is complete before I attempt to fill the holes, so that I do not plane away my plugs. It is unsusual to use wood with holes in it like this, but it is also unusual to use anything other than maple for a violin back. Five-string bluegrass fiddles are not burdened by the same 300+ years of tradition as violins, though, so exotic woods can be used. This wood has amazing flame and figure in it, and the plugged holes will not detract from the beauty of the wood.

Before I begin arching, I establish the edge-thickness all the way around, using a “wheel-style marking gauge“, set to 4 mm. It has a tiny sharp wheel that does the marking, and it makes very cleanly scribed lines.

Edge thickness marked on correct edge. (Notice the bark inclusion on the other edge)

Beginning arching

I used a Japanese-style pull-saw to cut the approximate height of the plate thickness on each of the corners, so as to avoid unnecessary stress on the corners while carving the arching. It looks a little odd until the arching is complete, but it avoids the possibility of breaking off a corner. I use a large, sharp gouge to reduce the edges and begin the arching; then a toothed finger plane to continue the curves until I am very close to the desired shape. at that point I will switch to a smooth, curved-sole plane and bring the arching to nearly exactly the desired shape. From that point on, a variety of scrapers will be my only shaping tools, for fear of tearing out wood along the figuring .

Here are some photos of the progress. This is very hard, difficult wood to carve, and my hands are giving out, so this is about as far as I am going tonight:

Beginning arching 1 — Beginning arching: notice the saw-cut corners, and how the one has been carved almost to a normal curve.

Arching back plate in cradle — Different viewing angle: The cradle is thick pine, with a plywood door-skin, to secure the plate. Inside, it is cut away, so that the plate can fit arched-side down. The plywood is right at 4mm thick, same as the finished plate.

Continuing arching back plate — Continuing arching. Still quite a way to go, but I am getting tired.

So…that is it for today. Pretty fancy wood, isn’t it? The customer bought it in Hawaii 33 years ago, or so, and has dragged it around all these years, until he decided that he wanted a five-string fiddle. Probably the only opportunity I will ever have to make a fiddle out of curly Koa, but it is really going to be a beautiful instrument.

My hands are getting too tired to work effectively. I will try to get more done later this week.

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