Posts Tagged ‘shaping’

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.

 

Thanks for looking.

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5-String Fiddle Progress Report #5: F-holes and Bass-Bar

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F-holes and Bass-bar

F-hole Drill

We had just completed the graduation in the last post; Usually, by this point, I am beginning to see the interior of the f-holes, too, because, as you may recall, I had incised them pretty deeply. In this particular case, I could just barely see some portions. I guess they were not as deep as I thought they were.

Once the inside is complete, I finish cutting the f-holes. Many people use a jeweler’s saw, a fretsaw, or a coping saw to cut out the f-holes. I generally just use the knife, except that I do have a special tool for cutting the round upper and lower eyes. I didn’t take any photos of it this time…here is one from an earlier instrument:

f-hole drill

F-hole drill being used to cut the lower eyes on a cello.

f-hole drill and holes

F-hole drill with completed eyes and cut-out plugs.

F-holes Completed and Clean

Just getting the f-holes cut is only part of the job…they need to be clean, and smooth, and relatively symmetrical. I will keep touching them up and tweaking them until the day I begin the varnish, most likely, but here they are; close to being complete, if not completely done.

f-holes

F-holes essentially complete.

By the way, you may have noticed that on this instrument (and the last one) I purfled after installing the plates. I was taught to purfle early, but I always had trouble getting my overhang even, and my purfling parallel to the ribs. So I tried purfling after closing…works fine and looks better. Diff’rent strokes, I guess….

Bass Bar

When the f-holes are complete, and clean, I can fit the bass-bar. The bass-bar is a spruce brace supporting the bass-side of the bridge, and providing for a good sound on the low strings.

I lay out the location of the bassbar, 1/14th of the width off center, at both upper and lower bouts. It usually ends up about 15 mm off center at the lower bout and 12 mm off center at the upper bout. (Those were the exact measurements this time: the upper bout was 168mm wide and the lower was 210 mm wide. So 1/14th of each was 12mm and 15mm respectively.) When I lay the bass-bar blank along that line, the side of the blank should just about “kiss” the upper eye on the bass side. I make slight adjustments as needed to make sure it does not obstruct the f-hole at all, then scribe the line in with a flexible steel ruler and a soft pencil. The line ends 40mm from each end of the plate, so the bassbar is just under 11″ long, (and about 7mm thick where it contacts the plate, tapering to 5mm along the free edge.)

bass-bar layout

Bass-bar layout lines complete.

Chalk-Fit Trick

Then I do something a little unusual: lots of luthiers chalk-fit bass-bars…in fact, probably most of them do. I have only known one or two who can successfully “eye-ball” the thing in. But I do not like the looks of chalk-residue mixed with hide-glue, either. I can’t see the white chalk clearly enough to use it, and the others leave an ugly residue– expecially the green or blue chalks.

So… what to do? Someone, years ago (can’t recall who…probably my friend Jake Jelley), pointed out that the paper gauze tape sold in pharmacies will stick securely, you can see the line through the tape, and it holds the chalk very well. The tape (3M Micropore) is so thin and fragile that you get a very good fit, but when you take the tape off after the fit is perfect, all the chalk comes off with it. (Careful! It can pull splinters off, too!) Hey, Presto! Clean wood, and you are ready to glue in the bass bar!

Pre-Fitting the Bar

I pre-fit the bass-bar by eye, using a compass to mark the contour from both sides, then trimming with knife and plane until the fit is close.

Bass-bar pre-fit.

Bass-bar pre-fit by eye, using a knife and plane to trim the wood to a close fit. Chalk-fitting is next.

Then I apply the paper tape, darken the line on the tape as needed, and begin the chalk-fit process. It is important to learn to JUST plane or scrape away the portion of the bass bar with chalk on it, on each try. Don’t plane off whole sections…it is possible that only that one little place with the chalk was high.

paper tape for chalk fit.

There is the paper tape…you can still see my layout lines.

chalk-fitting bass-bar

Beginning chalk-fit.

chalk-fit complete

Chalk-fit complete, and tape removed. Notice the arrow on the upper end of the bar: that is to keep me from forgetting which end is which.

Final Check and Installation

I check the fit by clamping the bar in place, dry.

bass-bar dry fit

Dry fit and clamped for final check. Seems to fit acceptably…

Then I remove the clamps, and slather on the hot hide glue–carefully. I quickly re-position the bar and clamp it securely, then clean up, using hot water and a brush. The small amount of watered-down glue soaking into the wood around the bar doesn’t seem to hurt anything, so I don’t worry about it.

bass-bar glued and clamped

Bass-bar glued, clamped and brushed down with hot water.

Shaping the Bass Bar

When the glue is completely dry, I remove the clamps and shape the bar…”just so”.

sketched shape of bass-bar

The glue is dry… see the sketched-in proposed shape of the finished bass-bar. The dark area beside the bar is just a shadow, not glue.

I do not have a “scheme”, here, and I do not measure it beyond occasionally checking the center height. I am just going by feel, by eye, and by experience. I know if the bass bar is too weak, it will affect the sound of the bass string…so I err on the side of a tall bar. I am certain that many will frown upon this. I am not telling you how you should cut a bass-bar; just sharing how I handle mine.

So; I use gouges and finger-planes initially, to shape the bar, finishing up with scrapers, files, and even sandpaper. (Yes, I know…but it’s OK, honest!)

And…there’s the plate, completed and ready to install! Well…sort of….

The glue was a little too thin on one end of the bar and it popped off for about a 2″ section. So it has been re-glued and is drying.

bass-bar nearly complete

Bass-bar nearly complete. One end popped loose, and needed re-gluing.I will do a little final shaping before calling it done.

Besides, the inner edges of the plate will have to be rounded and smoothed before I can actually install it. But there are probably less than 30 minutes of work left before I can glue the front plate in place. So it’s almost done. I hope to install it tomorrow, but I have some other things to do, as well.

Some of you may wonder why I install the front plate first; I was actually taught to do the back plate first, and to install the neck last, but it finally occurred to me that I could fit the neck before installing the back plate, and before removing the mold, and get a perfect neck-set, then trim the back of the heel flush with the rib plane, and install the back last, after removing the mold and cleaning up the interior. It worked very well, so I have continued the practice. Again; different ways of doing things result from different skill-sets and different problem-solving methods. There is nothing wrong with either way. (I even knew of a fellow who set the neck before installing either plate…but I can’t see that one. On the other hand, that guy made over 1000 instruments before he died, and sold every one of them; he must have been doing something right.)

So, the next post will involve completeing the neck and fingerboard assembly, installing the front plate, and setting the neck. Could be a week away; I am going to be working a lot of overtime on my day-job, for the next several months it seems.

Later the same evening:

finished bassbar 1

Bassbar is finally complete!

bass bar side view

Side view…lighting is difficult, but you can see the profile.

Thanks for looking.

Chet

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