Sunday, 27 October 2013

Hook Knives

 These rather strange looking curved blades were nearly an extinct tool until the recent renaissance in green- wood working.  The wooden table ware (called “Treen”) that they are instrumental in producing has been ubiquitous throughout Europe for millennia, only in recent decades has industrial process allowed ceramic bowls and plates to become truly commonplace at the table. That said, as recently as the 1950’s and 60’s there were still regions of the UK where the Turners could still be found producing green wood wares for everyday use and more commonly on the continent.

The knives appear, outwardly, to be a simple thing- a bent, single edged blade- however when one sets about to use and make them their hidden complexity becomes apparent…

The difference between a hook knife being a pleasure and a pain to use is subtle and nuanced, a matter of Geometry and attention to detail.

Firstly, the blade blanks are forged. The steel I am using here contains between 1.1 and 1.2% carbon.

The first point of interest that we come across is that in order for the inside of the blade to be flat on the finished, curved knife, they must first be hollow-ground whilst the piece is still straight.  This is because the inside of the knife will be compressed when it is bent- making the interior cross section convex, if the forged-in flatness was left uncorrected.


Additionally, the blunt edge must be ground to a radius that doesn’t interfere with the curving cut, this again is done when the blade is straight.

The bevel at the edge is also partially ground at this point as it would be close to impossible to grind one evenly once the piece is curved. If it is left too thick, it will more difficult to sharpen after hardening as it will be… well, hard. If it is too thinly ground, the edge can be easily overheated causing the steel to lose carbon and thus making it harden less effectively.

These different shapes can be seen together in cross section.

After this first grinding phase the work is reheated and the initial, acute bend in the ricasso (blunt) area is put and the curve is delicately put in either around a former for the consistently radius “twca cam” style traditional knife or freehand for the modern, versatile “compound” hook.  Care being taken not to damage the ground in cross section, which could be easily done whilst the metal is soft.
Twca Cam blades

Once hardened they are tempered for an hour to relieve the brittleness and then ground sharp. This is tricky because each blade must be continuously moved to keep the grind smooth and even. The blades are sharpened and polished with a high grit buffing compound, leaving a mirror finish.
After final sharpening I give each blade its second temper for an hour to ensure it is fully stress relieved and at it’s most resilient.
The tempering process causes a range of oxide colours to form on the steel surface, these colours precisely indicate temperature. This golden colour, whilst permanent is exactly one molecule thick and so, easily removed with a gentle stropping- it is, though, very beautiful and as such I have been leaving it in place as a proof and a decoration.

These knives are an interesting thing to make and ive been very satisfied with how well they cut.

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  1. Beautiful work. Any pics of them in use?

    1. Thank you very much John, ive got a few pics I could put up on the next blogpost for you. Thank you so much for looking.