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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.


  • 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.

[I’ve stopped using the wood screws, its easy enough to bend to the line. Jan 2015]



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 can be 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 balked 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.



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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.




I’ve had several requests for mold dimensions. Here is an outline of my most used version. The length of the mold, omitted in the drawing, is 314mm


The skeleton mold became the basis of my journey into the wild world of Freestyle Violinmaking