A “Violin knife” refers to a traditional tool used in both violin making and in broader luthier and wood working. The basic violin knife is a long relatively narrow piece of tool steel sharpened with an angled ‘blade’ at one end, double beveled and inserted in a removal wooden sleeve handle. What the knife is used for varies on the width of the steel, the angle of the blade portion and the bevel angle.
The blade portion can be made by tempering any high carbon steel, or ready made blades can be purchased from suppliers like Pfeil or Hock. The handles typically are separate and can easily be made in the workshop.
The size of the knife describes the width of the stock. Because the blade can be moved forward in the handle it can have a very long working life, making it an economical tool.
Michael Darton uses a 18mm knife with a curved blade for fitting bridge feet, a 16mm knife with a straight blade for sound post fitting, a 13mm knife with a long curved tip for shaping cello bridges and rough jobs, a 10mm straight edge for cutting f-holes (dedicated), and a 3mm knife with a long sweeping edge for shaping violin and viola bridges.
In Weisshaar and Shipman’s book on violin restoration they recommend a steeper ground bevel for hardwoods than for softwoods, and notes the importance of a good “f-knife”. They also point out that the removable handle provides the cutting edge with extra reach, particularly for neck grafting.
A handle is easily made in the shop from three layers of wood. By selecting the thickness the middle layer you can choose to friction fit the blade or have it held by a set screw. I used ebony and maple for the 6mm knife and epoxy to hold it all together.
Tip: to insert and remove the knife from a friction fit handle. Hold the cutting portion of the blade in a wooden bench vice and move the handle on and off the stationary blade.