Mandolin Construction Methods

Hollowing the plates

I have long looked for a safe way to hollow the plates for violins and mandolins. I was taught to do this using a spoon gouge at the violin making class I attended but this is quite a vigourous process and Mr Cockup is always in close attendance! If I was making in sufficient quantities I would not hesitate to make use of Computer Numerical Controlled (CNC) milling machines to produce plates that only require the final tuning to complete.
A professional violin maker here in Cambridge England David Rubio has developed a time saving way of removing the majority of the wood when hollowing the plates using a wood bit. I have had a description of his methods and have simplified it to a style that can be applied by any maker with a pillar drill of modern design available.
 

drill machine setup for plate hollowing

 The Drilling machine is fitted with the blockboard table extention that I made to use when thinning the sides. The hole in the centre of the table is used to locate a domed piece of 3/8 plywood. The dome should be sufficient to ensure that the outside of the plate is able to contact the apex of the dome directly under the cutter. If the dome is too shallow the accuracy of the process will be compromised.
For a close up of the domed support go here. Since I took this picture I have increased the doming significantly (the height of the edge is now 3mm where as it is about 7mm in the picture).
The cutter is a Forstner wood bit. The one I use is modified from one intended for use in a brace. In order to make it usable in a pillar drill I had to cut off the square shank and turn the shank to a parallel diameter. These drills can be obtained for use in pillar drills and this would be the best course for most people. The cutter shown is 3/8" diameter and this seems to be the safest size.

picture of the cutter

setting the drill machine depth

 The cutter is set to descend until just short of the desired thickness NOTE The small point on the drill is the defining depth. I use a drill of appropriate diameter to check the depth setting. The instrument I am making at present is intended to be as close as I can get to the Lloyd Loar sizes as shown on the Guild of American Luthiers drawings. This means that the back thickness will be 4.0mm at the centre. I used a 5mm drill to set the depth thus giving me a 1mm safety margin. When I get more familiar with this method I will set the depth to be closer to the final size (probably 4.3mm in this case).
The drilling machine used MUST have a good reliable depth stop.
To effect the material removal, the point of the cutter is entered into the wood and the cutter fed smoothly into the wood until the stop prevents further movement. The cutter can overlap previous holes as the centre point fixes the location and stops the cutter wandering into the previous holes. Some care must be taken to ensure that the overlap is not too large or the cutter will wander.

cutter doing the plate hollowing

Close-up of the cutter working

 The overlap can be seen in this view. Once the meat has been removed the rest of the thicknessing is done using the traditional violin makers planes. I use the depression left by the centre point of the cutter to act as a guide for planing. I work the surface until I have just removed the pits and then I know that I have achieved an even thickness that is the same as the diameter of the drill that I used for the depth setting

  • Making and using an electric bending iron Some pictures of my bending iron in use

  • Simple rib thicknessing Using a pillar drill to simplify the process of reducing the ribs to the correct thickness

  • The contour method of arching measurement This is the way I was taught to do the arching on a violin and the method is just as applicable to the mandolin.

  • Trussrod infromation Description of how a trussrod works and how to adjust one safely. This is general information for all instruments fitted with a trussrod

  • Tuning the plates for optimum performance Using an electronic vibration method to create Chladni patterns from which the likely performance of the plate can be deduced

  • Things I have picked up from other makersSome real information, some hearsay, some old wives tails.

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