Violin shop

Smaller cello: Guadagnini model

arc — Wed, 28 Dec 2011 21:09:13 +0000

Kochanski del Gesu model violin

arc — Fri, 25 Nov 2011 19:43:41 +0000

My 2011 rendering of the Kochanski Del Gesu.

Violin patching using a vacuum bag

arc — Sat, 19 Nov 2011 23:00:24 +0000

In 1992 I wrote an article for The Strad magazine about the use of a vacuum bag in the process of fitting a reenforcing patch in a cello. In that example I cut a hole in the bag around the patch area and sealed the edges of the bag to the to the cello top. In this way I got access to the work area but maintaining a tight seal was a bit challenging. Subsequently I have found that in many instances it works better to seal the top and mold completely in the bag, fit the patch onto the plastic and then remove the bag just prior glueing the patch in place. This works best in where the patch profile has a shallow dish to it.This patch on a viola top is a good candidate for using a vacuum bag. The patch area has been thinned out by a previous repairman and is quite flexible, it does not lie flat in the backing plaster mold. This makes it difficult to accurately chalk fit the repair wood into place. Placing the job inside a bag and sucking out the air the violin top will be pulled down firmly into the mold giving a good surface to work on. (Note the “V” marks on the patch edge – explained below).

Rough fitting the patch. New patch wood has been placed into the patch area, the chalk shows where the patch is making contact , the chalked areas of the patch are cut off and the process is repeated.

The viola top has been taped into place in the plaster mold and sealed into the vacuum bag. The bag I used is only 0.01mm thick, about the same as a supermarket vegetable bag. There is a valve in the line near the bag, this allows me to control the rate of evacuation and avoid wrinkles in the work area

Here is the little vacuum pump. I have it on a long line so that it an be in the other room while I’m working. The green thing on the end of the line is a scouting pad to stop the line end getting sealed by the plastic bag

Pump details

Under the plaster mold I put a sheet of thin foam to help avoid punctures when I clamp onto the mold

I use cardboard as locating tabs. Chalk applied to the bags surface sticks very well, there seems to be some kind of electrostatic attraction between the chalk and the plastic.

The new patch wood has been placed into the patch area, the chalk shows where the patch is making contact , the chalked areas of the patch are cut off and the process is repeated

After rough fitting with chalk I switch to oil paint as a marker, this is essentially turning the plastic surface of the bag into carbon paper. I hesitated a long time before trying oil paint as a marker because I feared the the presence of oil on the wood surface could weaken the final glue joint between the patch and the viola top, but in the end I figured that all of the oil gets removed in the cutting process. I’ve found that Ultramarine works well, it has a smooth texture and a fierce tinting nature.

The oil paint is much easier to “read ” than chalk……

….even in the later fitting stages……..

…….and it removes completely before gluing.

It is possible for the card locating tabs to creep during the fitting process so when a final fit has been achieved, just prior to removing the plastic bag, I mark on the patch edge the points at which it intersects with a series of diverging lines marked on the viola top (also see picture 1). In this way the exact location of the patch can be replicated for final gluing. (click on the picture for a closer view).

Glueing in the patch. The plastic in the patch area has been removed prior to glueing.

The new patch is trimmed to final dimensions.

A cello top inside a contractors bag.

When using a thicker bag, which is less likely to puncture, I glue a temporary wooden locator to the cello surface inside the bag.

Showing how well the chalk adheres to the plastic. Oil paint could be used instead of chalk.

Replacing a violin neck

arc — Fri, 18 Nov 2011 14:29:12 +0000

A correctly dimensioned and properly positioned neck is crucial for the functionality of an instrument. A skilled violin maker can also use the neck to make significant tonal adjustments. There are many variables in neck dimensions and most makers have their own views on what is optimal. If the neck has been broken, or excessively worn, it may have to be replaced. in this example the old neck had an accumulation of minor problems and the quality of the instrument justified the expense of fitting a new neck.

The procedure outlined here is the same as that to which most classic period instruments were subjected in the 19th century when the broad, low angled baroque necks were replaced with modern necks. The scroll, which must be preserved as part of the original instrument, is grafted onto a block of wood which will be used to form the new neck.

Problem 1: head crooked on the neck. It can be surprisingly tricky to get the head in line with the neck. If the head is twisted or warped you may have to choose between aligning the front view or the rear view or splitting the difference. I felt that this one could be done better.

Problem 2: neck wedge. This neck was been “wedged”; a maple fillet has been added under the fingerboard to increase the angle at which the neck meets the body. This is a valid repair when the only problem with the neck is the neck angle, and when the cost of replacing the neck isn’t justified. This job could have been refined by making the wedge out of ebony, which isn’t so immediately visible. Also the neck, which has become rather thick, could be reshaped.

Problem 3: neck not aligned to body. Sighting down the fingerboard to a bridge placed centrally between the ff-s shows that the neck has been stuck on crooked. This is the most serious of this neck’s problems. If the fiddle is strung up like this, the bridge will be pulled towards the bass side by the strings, and the tone will probably suffer. There is really no cheap fix for this; removing and regluing the fingerboard will make the strings run along the middle of the board but the string pull will still be uneven.

Considering the multiple defects, and that it is a nice fiddle that deserves better, it’s time for…..

Neck removal – free the mortise sides. A thin-kerfed saw is used to cut each side of the neck root to the depth of the old mortise. If the two sides of the neck joint are not completely released there is a real danger of splitting parts of the ribs off as the neck is removed.

Free the neck root at the button. This Japanese saw, designed for making a cut in the middle of a panel, is ideal for starting the cut to detach the neck from the button. The curved blade helps to avoid accidentally cutting the ribs.

Incidentally, notice how small the button is, it has been trimmed after a previous neck resetting. This is very bad practice but tends to happen when it is not cost effective to do the job properly, ie by making a new neck. Before setting the new neck, I will build this button back up with an ebony crown so that the finished neck will have the correct dimensions for strength and looks.

Cut down into mortise. Using a modified version of of the previous saw the cut is continued to the bottom of the mortise. This ensures that the button won’t be damaged when the neck is removed.

When the saw cuts are judged to be deep enough, the neck will given short sharp blows to the side until it comes away from the body (this step is not for the faint hearted). If the neck joint was made well, some splinters of the top block will come away with the neck but, because of the careful preparatory sawing the button and ribs are preserved intact.

Bush the peg holes. When the violin head is spliced onto its new neck, the joint will extend up inside the peg box as far as the G-string peg hole. To provides a solid, continuous surface to work with when splicing in the new neck, the first two peg holes are filled with a wooden bushing. If the peg holes are large and worn this is a good time to bush all four holes so that a new set of pegs can be fitted. In this case the pegs were in good shape and had fairly narrow shanks, so it was decided to do the least work necessary and only bush the E and G.

Trim the bushings. Using a shallow-sweep gouge, the bushings are trimmed off flush with the pegbox surface.

Off with its head! No matter how many times I do this I still feel a little squeamish.

The bone pile – old violin necks. Some of the ebony fingerboards get recycled into neck wedges and top nuts; the rest are keepsakes.

Cut the mortise. The tapered slot that the new neck will fit into extends up to the second peg hole. This gives an adequate gluing surface for a strong joint. There are several styles for cutting this joint; this is the French style and is the simplest, least invasive and is adequately strong. The English style calls for a taper that ends in a butt-joint at its small end. It is trickier to cut and gives no advantage.

Clean up the inside of the mortise.

Check the mortise. Using a “paddle”, a flat piece of bass wood, the mortise surfaces are checked for true. When the paddle fits without rocking the fit is further refined by chalking the paddle to reveal high spots. These are then removed with chisels, knives and scrapers.

Preparing to cut the tenon. The lines of the mortise are transferred onto the new neck block.

Fit the neck block to the head. Not only do the three surfaces of the joint have to meet perfectly, but the way that the head is mounted on the neck has to be monitored. There are five dimensions to be watched; in this picture I am checking the clearance of the neck projection at the scroll. This determines whether the head looks crooked and it also ensures that later on it will be possible to plane the neck surface without accidentally planing the top of the scroll.

Prepare for gluing. Several counter-forms are needed to successfully hold the head in place as the glue dries. When hot animal glue is applied to the mortise the water in the glue swells the inside of the thin pegbox walls, causing them to flare outwards. The visible edges of the joint no longer meet and all hopes of an invisible join are dashed. Very close-fitting counter forms are needed hold the pegbox in place. Before applying glue I cast a pair of counter-forms from dental impression compound backed with wood and lined with masking tape.

Another detrimental effect of the fresh glue is to lubricate the joint so that the tenon slides in past the location it was fitted to. This would result in spreading the peg box out past its original width. A small wooden block has been glued to the back of the tenon to act as a stop.

Joint glued, counter-forms hold parts in place as glue dries.
The inside of the pegbox is re-carved.

A new finger board is prepared. Now that the final position of the head is known more of the excess neck block can be removed.

New board in place, ready to start the neck set procedure.

Skeleton molds

arc — Tue, 15 Nov 2011 04:11:53 +0000

Violin rib construction methods

The sides or “ribs” of the violin are most commonly constructed of six thin strips of wood, reinforced where they meet at the corners and ends by small blocks of wood. The problem during construction is how to hold those blocks and sides in place while they are being shaped and assembled. There have been several solutions to this problem, the most popular these days being the “inside mold” as used by the major classic Cremonese makers. Other methods include the “outside mold”, “building on the back” and “spanish guitar style”. Each method has its own advantages and demerits depending on what the maker’s aim is, the outside mold for instance gives a high degree of control over outline and has been favored by copyists looking to reproduce the non-matching outlines of the back and top of an individual old instrument. It is also favored, by odd contrast, by makers seeking extreme symmetry and reproducibility, it is famously used by 19th century French production manufacturers and is partly responsible for the uniformity and relatively stiff look of some of those instruments. One method that is rarely mentioned is a “skeleton mold”. I came to the idea a couple of years back when I wanted to make a Guadagnini model violin but was too impatient to go through the process of constructing a new inside mold. I decided to make a mold that had just enough structure to hold the blocks in place but carried no information about the outline of the finished instrument. My skeleton mold was born partly from laziness and partly from the enjoyment of trying new techniques and seeing what they will reveal.
What I found surprised me, a rib construction method that is simple to set up and which allows a broad range of control or improvisation depending on the maker’s personal inclination. I don’t think that this method is new, since adopting it several years ago I have heard passing reference to some older German makers using it (and I would be grateful for any further references to it’s use), but it is not mentioned in most reviews of construction techniques that I have seen. The skeleton mold has some significant advantages over other rib construction techniques which I list here and will demonstrate in contrast to the popular Cremonese style, inside mold.

Advantages of the skeleton mold

Quick set up: one mold serves for an infinite variety of rib outlines.
Adaptability: improvements to an outline can be made simply by producing new templates rather than by correcting imperfect molds. On-the-fly adjustments and improvisations can be made with easy reference to a baseline.
Control: I was surprised to find how easy it is to bend ribs to fit a drawn line.
Access to inside of rib/block and rib/lining joints. Joints can be checked and cleaned up during construction rather than having to correct any errors after glue has dried and the mold is removed.
The inside line of the rib structure can be directly traced onto the top and back plates removing any guesswork about how far the internal hollowing can be taken.
Light weight and easy handling: particularly significant on cello molds.
Storage: store only drawings and templates for each new model of instrument.
The work board provides a cheap, disposable surface for cutting and trimming on, it also allows the job to be easily and safely clamped to the bench. This is particularly handy when chopping in the C-bout lining mortices.

Disadvantages

Every construction technique leaves some tell tale signs (beloved of connoisseurs) on the finished instrument. If capturing every detail of a given instrument is your aim then adopting the identical construction technique might be a more fruitful path to follow.

Using the skeleton mold

The traditional Cremonese style mold follows exactly the inside line of the ribs. Notches are cut into the mold to receive the corner blocks. The blocks are shaped to receive the ribs, the ribs are bent to fit the outside line of the mold and can be pulled tight against the mold to correct slight inaccuracies in bending.

The skeleton mold provides no indication of the shape of the finished instrument, it merely serves to hold the blocks in place while shaping and locating the ribs.

Skeleton mold layout with reference to the internal rib line. One mold will accomodate an infinite variety of rib outlines, which makes adjustments to outlines easier – simply cut a new template rather than a complete new mold. It also helps for storage, many templates being much less bulky than many molds.

The instrument will be built on a work board. Each new instrument starts with a clean sheet of paper taped to the board and a pair of locating pins set in place.

A template keyed to the locating pins is used in making a clear outline of the rib pattern. In this case I’m using a half template which is flipped to make a symmetrical layout. To capture a little of the asymmetry of an original instrument a full template can be used.

The mold is set on the locating pins. A wood screw set into the C-bouts makes a useful back stop when fitting the C ribs.

With the corner blocks glued to the molds the outline pattern is marked onto the corner and end blocks.

The corner blocks are cut to receive the c-bout ribs. The work board provides a cheap, disposable surface for cutting and trimming, it also allows the job to be easily and safely clamped to the bench. This is particularly handy when chopping in the C-bout lining mortices.

Blocks cut to follow outline, ready for the ribs.

The C-bout ribs being glued to the blocks. Being able to clamp directly to the back edge of the corner block gives a great advantage over the traditional inside mold.

Checking the final fit of the rib on the block and cleaning up the glue squeeze out like this is not possible with the Cremonese mold.

After the C ribs are set in place the remaining blocks are cut to shape and the outer ribs are bent and fitted in place. It is actually easier than might be imagined to bend the sides to a line rather than to the edges of a traditional mold. After bending on the hot iron a certain amount of fine “fitting” can be done by changing the rib’s location on the blocks causing them to bend a little. Of course this technique can also be used if you are in the mood for a little improv; use the penciled rib line as a reference for controlled deviation or try free-styling on a blank sheet of paper - may the Force be with you! Find the spot where the ribs best fit your line, dry clamp the ribs and mark the block location on the rib before final glueing.

Glueing the ribs to the blocks on a backing board ensures that the ribs end up following one straight plane. Having the board lined with paper removes any worries about accidentally glueing the rib structure to the board.

Being able to check the fit of the linings and clean up any glue squeeze-out (not to mention avoiding accidentally sticking the linings and ribs to the mold) is a great advantage over the Cremonese mold where the underside of the linings are hidden until the ribs are removed from the mold. Usually after removing ribs from a Cremonese mold there are one or two areas of the linings which require attention just prior to glueing the ribs to the plates.

The linings can either be trimmed now or after the ribs are removed from the mold.

Transferring the rib shape to the back plate. Following the same procedure as with the Cremonese mold, a washer provides an off set for the “overhang” or “margin” of the plate.

The inside line of the ribs is marked directly onto the top and back plates. This is not possible when using the Cremonese mold; with the skeleton mold you know exactly how far you can go with hollowing the underside of the plates.

Plates marked and ready to cut out and shape. The making process would proceed in the same way for either method from this point. One final bonus from using the skeleton mold method is the extreme ease of detaching the ribs from the mold.

A skeleton mold for cello. I was nervous that the larger ribs would be uncontrollable but my worries proved to be unfounded. In this case I cut the shape of the C-bouts into the mold so this mold is not as universal as the violin and viola molds – you can easily vary the upper and lower but shapes but the C-bout is fixed. This mold was an absolute joy to use: light (only 1Kg compared to 3.2 Kg for my traditional mold) and with many convenient hand holds. When I recently made a double bass I baulked at using a skeleton mold; the ribs were just too big for me though I would imagine that an experienced bass maker could do it fairly easily.

Making a copy of a smaller Guadagnini cello was an ideal application for the skeleton mold. I wasn’t sure how many of these I would be making, but by using a skeleton mold the setup investment was small and the turn around quick.

Copy of the Kochanski Del Gesu made for Robertsons and Sons Violins, constructed on a skeleton mold. In order to capture the feel of the looser outline on the original instrument I made a full body template of the rib line for the back incorporating some of its asymmetries.