Posts Tagged ‘clamps’

More Progress: Plates and Scroll.

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More Progress: Plates and Scroll.

Completing the Back Plate

I continued planing away wood from the inside of the back plate until it was very nearly correct, then switched to scrapers, and completed the inside surface, so that it looks to be a smooth continuum of curves, transitioning without a ripple. The  plate will require no further attention until I am ready to install it. Unlike the front plate, I intend to install the purfling later, after I am completely sure how the garland will respond to having the mold removed (sometimes they can move, and change shape a little.)

Back Plate Graduation complete.

Back Plate Graduation complete.

 

Scroll Progress

I also continued working on the scroll. My hands were getting pretty tired, so I took a break from that. It is still quite rough, but, here’s how it looked at break time:

scroll beginning

Long way to go.

 

scroll progress

On the right path, but “miles to go before I sleep.”

 

Bass Bar Fitting

To fit a bass bar, I begin with a completed front plate, and lay out the position of the bass bar, so that the distance from the center to the bar, level with upper and lower bouts at maximum width, is 1/7th the full distance from centerline to the edge at those respective points. Usually, that means that the lower point will be about 15mm from the centerline and the upper one about 12mm (as it is in this case.) I lay out a line through those two points, and observe where it is, nearest to the bass-side f-hole. If it is too close, I “fudge” it away, a bit, trying not to change the angle. (The bass bar has to clear the f-hole.) Then I mark the two ends, 40mm away from the ends of the plate, and that is the place to fit the bass bar: the “footprint”, so to speak.

Bass bar position laid out.

Bass bar position laid out.

 

I use chalk to fit my bass-bars. I have never had a good enough eye, and a sure enough knife-hand to accurately fit a bass-bar without the use of chalk, though I have known master makers who regularly did so…perfectly. (Sorry… I’m not good enough for that.) On the other hand, I have had some nasty experiences with the residue of blue chalk mingling with the yellowish hide glue when installing a bass bar: it left a very ugly green stain…and it never completely came out. So…what to do? In the first place, I switched to pink chalk. If a little chalk is left, the glue will simply make it look a bit orange. (No problem.) But, I really don’t want chalk residue at all.

A friend showed me the paper “gauze” tape available in pharmacies. It is thin enough to completely conform to the surface of the plate, and  produce a good fit, and, it is slightly translucent, so I can see my layout lines through the tape, and keep the chalk on just the path of the bass bar. I first use a compass to mark the general shape of the bottom of the bass bar, and then trim it with a knife and a small plane. That gets me “in the ball-park,” so to speak. After that, it is chalk-fitting time.

The front plate is made of European spruce, but I chose Sitka spruce for the bass bar. There is quite a contrast in color between relatively fresh European spruce, and well-aged Sitka spruce. It actually made it a little difficult to see the pink chalk against the dark wood. But it worked.

Bass bar blank, knife-trimmed after tracing the shape with a compass.

Bass bar blank, knife-trimmed after tracing the shape with a compass.

 

paper gauze tape

This is the paper gauze tape I use for chalk-fitting.

 

Paper gauze tape and pink chalk

Paper gauze tape and pink chalk, ready to begin chalk-fitting.

 

Layout lines visible through the tape.

Layout lines visible through the tape.

 

Layout lines traced over on the tape, to make them more visible.

Layout lines traced over on the tape, in pencil, to make them even more visible.

 

Chalk on tape.

Chalk on tape.

 

Chalk transferred to bass bar

Chalk transferred to bass bar

 

The idea, in any chalk-fitting procedure, is to press the fitted part (being fitted) into the chalked surface to which it is being fit, then trim away only the portions where the chalk transferred. So, in the case of the bass bar, I need to press it into the chalked top plate, and then check the bottom of the bass bar blank, to see where to cut. I trim off the obvious spots, and try again. Ideally, every time I try, I will get a broader transfer of chalk. When the whole area gets a light dusting of chalk at one time, the fit is as close to perfect as I can get it. I remove the tape, wipe off any chalk residue, slather the hot hide glue onto the bottom of the bass bar, and clamp it home. On a good day, it takes me a half-hour. On a bad day? Don’t ask… 🙂  This time wasn’t bad, though.

Chalk-fitting complete; Dry-clamped to check fit.

Chalk-fitting complete; Dry-clamped to check the fit.

 

Tight fit

The fit is good!

 

Glued and clamped

Glued and clamped. 

More Scroll Progress

While the glue was drying on the bass bar, I went back to work on the scroll. It was looking verrry rough when I had to take a break, so it is nice to see it progressing better, now. There is still a lot to do. I have to excavate the pegbox, and cut the fluting in the volute. But this is as far as I am going tonight. I am glad to call it a night, and let my hands rest.

More scroll progress

More scroll progress: there is still a long way to go, but it is looking better.

 

Scroll partly complete.

Final status for tonight. Looking a lot better, and more encouraging to see.

 

I have other things to do tomorrow, so I may or may not get to work on the violin. At the very least, I expect I will be able to trim the bass bar to the shape I want it, but beyond that, I don’t know.

 

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The Garland

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The Garland

Shaping blocks and Bending ribs:

Inner curves of corner-blocks, and both end-blocks, first

I learned to shape only the inner curves of the corner blocks, initially, as well as the outer curves of the end blocks, because if I shape both curves on each corner block, then there exists the possibility that, when I clamp the center-bout ribs in place for gluing, the tips of the blocks may deflect outward, instead of holding their respective shapes.

Also, after the c-bout ribs are glued in place, when I shape the outer curves, in preparation for receiving the upper and lower ribs, I shape the ends of the c-bout ribs at the same time, so that they simply continue the curvature of the blocks, to a feather-thin end condition, before gluing the upper and lower ribs in place. Then, when I trim the upper and lower ribs, it is easy to make the glue-lines between the c-bout ribs and the upper and lower ribs completely invisible, matching the corner of the trimmed ribs at the corners of the instrument garland.

So, here is the mold with the blocks shaped as described above:

Blocks shaped in preparation to installing certer-bout ribs.

Blocks shaped in preparation to installing certer-bout ribs.

 

Ribs are Next

When using figured wood, I have to make a determination as to which angle the figuring will follow on the instrument. I thought I could just copy whatever the Old Master (Guarneri del Gesu) had done, but, as it turns out, he used highly figured wood for the ribs, all right, but the flame (curl) in the maple went directly across the rib at nearly exactly 90 degrees, whereas mine is quite slanted. So, I have to make a decision: Will I have the curl slant “up” (north) from the back side to the front, or the other way– from front to back?

Really, I simply have to make it consistent, on both the treble and bass sides. Some makers have the slant in the C-bouts going the opposite direction from that of the upper and lower bouts. Some, also, have used a single rib across the two lower bouts, and thus had the flame slanting one way on the bass side and the other way on the treble, and then matched the center and upper bout rib curl to the lower bout rib, so that the grain was consistent all the way around, instead of being mirrored between the two sides.

That sounds good: but, in the first place, I haven’t enough rib wood to pull it off correctly; and, in the second place, it can potentially cause problems later on, if the plates shrink (they are made of wood, remember!) and the ribs have to be shortened a little, to match. If there is already a joint at the center, it is relatively easy to simply shorten each side by a millimeter or so, as needed, and re-shape the end-pin hole. But if the bottom wood is all one piece, the repairer will have to cut through that bottom rib, and establish a new center joint; so the two halves will no longer match perfectly, though it will be pretty close.

Anyway: I usually would first thin the ribs to a consistent one millimeter thickness, and then cut them to length, carefully laying them out as to location and orientation, before bending. This time, I consulted with one of my teachers, who assured me that Guarneri ribs were a little thicker. So, since the ribs came to me at 1.3 mm, I will consider that to be the ideal thickness for this particular instrument.

Ribs

Ribs for new violin (one is already on the mold.)

 

Then I can bend all the ribs, individually, and set them aside ready to be used. In the case of the C-bout ribs, I clamp them into the mold, where they will cool, and stabilize, in exactly the correct shape. Afterward, I used a small brush to slip glue into the joints, and secure the C-bout ribs permanently to the corner blocks.

First (Treble side) C-bout rib installed.

First (Bass side) C-bout rib installed.

 

Second (Bass side) C-bout rib installed.

Second (Treble side) C-bout rib installed.

 

When the glue holding the C-bout ribs had dried sufficiently, I shaped the outer curves of the corner blocks appropriately: You can see, in the  photograph, below, that the center rib-ends have been shaped along with the outer curves of the corner blocks, so that they will cleanly fair into the curves of the upper and lower ribs.

Final shape of corner blocks.

Final shape of corner blocks. C-bout ribs are shaped along with the corner blocks.

 

I then immediately installed the upper and lower ribs in their respective places. In this particular case, I chose to install the lower ribs first. After the glue dried for a few hours, I installed the upper ribs.

Lower bout ribs installed.

 

All ribs installed.

All ribs installed.

 

When the glue holding the upper and lower ribs had dried sufficiently, I trimmed the ends to the correct length, and filed them smooth. The only “end-grain” showing will be the ends of the upper and lower ribs at each of the corners. I try to make them square with the centerlines of the corner blocks, so that it gives the inpression of a “mitered”corner, but with no apparent glue-joint: the joint is exactly along the corner of the squared-off rib end. The first priority is to have the rib end at the right angle, so it will appear to be perpendicular to the plane of the garland. The next is to file them to look “square” with the corner, as I explained above. Finally, some creative scraping of the C-bout rib-ends will usually move the glue joint to be exactly on the corner of the upper or lower rib, and make it essentially invisible. This one is close:

Corner, nearly complete

Corner, nearly complete: a little more scraping will make that joint invisible.

 

Linings

The only thing left to complete the garland is to install linings on both the front and back sides. The way I have chosen to use my mold (“French” method…ribs flush to one side of the mold) precludes my adding the back linings until after I remove the mold. That is fine: I also intend to leave the mold in place until after I have set the neck, so I have quite a way to go on that step.

Not everyone installs the neck while the corpus is on the mold. I began doing it when building my first cello, and it helped so much with neck-setting that I have continued it ever since. I deliberately allow the heel to “run wild”, in terms of length (or height, depending on how you are looking at it), so that it protrudes past the back of the neck block a little bit. When all my other items (angles, measurements, etc.) are exactly correct, I glue the neck in place, and before installing the back plate, I simply trim the back of the neck-heel flush with the back of the corpus. Then the back plate fits perfectly, and I am not struggling to get that joint tight. But… I am getting ahead of myself…. 🙂

I cut strips of willow to the appropriate dimensions for linings and then plane them smooth; then bend them to fit the curves of the violin, and finally, cut them to the appropriate lengths, and install them. Willow responds very well to both bending and carving, which is why I prefer it for lining material. I can bend all the linings in just a few minutes, and they will all hold their shape until I am ready to use them.

Bent linings, ready to be cut to length and installed.

Bent linings, ready to be cut to length and installed. Willow is easy to bend: These linings all started out like the straight one in the photo.

After the corners are all dry and secure, and trimmed, I cut two small mortises in each block, to receive the linings; then cut the linings to exactly the right lengths for a tight fit. The linings serve two purposes: they strengthen the edge of the ribs, which would otherwise be quite fragile; and they triple the gluing surface area bewteen the rib garland and the plates.

When I have all the linings fitted correctly, I remove them one at a time, apply hot hide glue, re-insert the linings, and clamp them in place, using tiny spring clamps. Sometimes one or more areas are more stubborn, and require a heavier clamp. Then I use something with more authority.

Linings fitted, glued and clamped.

Linings fitted, glued and clamped.

 

So: there is the garland (rib-structure), essentially ready to use! Next time we will level the garland, and use it to trace the shape of the front plate. At some point before attaching the front plate, I will also trim the linings to a triangular cross-section, so that the inner edges taper to a thin transition, and do not add a stress-riser to the ribs. I’m not certain whether it would affect sound, but the Old Masters did it that way, so I will follow their example. The corner blocks also will be trimmed back to be fairly minimal. I will carve away the end-blocks to each be the shape of half an ellipse, but I will leave them fairly robust, for strength.

Mold with blocks, ribs and linings.

Mold with blocks, ribs and linings.

You can still see traces of ink and glue on the blocks, looking like gaps…that will all go away when I level the garland.

 

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Cello progress

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Cello ribs installed in the mold, glued and clamped to the blocks.

Yes, you have to keep the wood warm!

The weather outside persisted in temperatures hovering just above freezing, so I brought the project indoors, heated the joints with a heat-gun, brushed hot water, slathered hot glue and clamped ’em home. Good glue squeeze-out all around; should be very good joints.

All ribs installed–glued to the blocks in the mold. Next step is linings.

Next Step: Linings

Actually, the very next step is to trim the excess rib length off the corners, and smooth them so that they are square-ended and straight along the edges…and parallel to one another. But that is a small enough task that I will combine it with installing the linings. The linings are a pretty easy, pleasant step in cello building…they are easy to make, easy to install, and the work goes quickly. That is what is next, and I should have it done pretty soon. Nice weather or no. 🙂

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