box wood and tiny clamps
Many people will know my love-affair with box wood for spoon carving. Box is super hard and dense, it takes a wonderful finish and allows minute chip-carving, but it definitely has its drawbacks when making hinged spoons.
To go back a bit... the first hinged spoons I made were in woods such as holly, maple and magnolia. These are all hard dense woods but they all have an important difference to box wood - they have more 'give' than box. To put it technically, their Elastic modulus is much lower than that of box wood. Elastic modulus is described in Wikipedia as 'the ratio of the force exerted upon a substance or body to the resultant deformation' or the amount of force it takes to bend the wood a particular distance. Very stiff dense wood will have a higher elastic modulus than very flexible lighter wood.
If you take a look on the Wood database project site (http://www.wood-database.com/) you will find all sorts of technical information about lots of different woods, including their elastic modulus. Here are some numbers:
magnolia - Elastic Modulus: 9.66 GPa
american holly - Elastic Modulus: 7.66 GPa
hard maple - Elastic Modulus: 12.62 GPa
red maple - Elastic Modulus: 11.31 GPa
and then there's box wood - Elastic Modulus: 17.20 GPa
Box is between a half and a third LESS elastic than these other hard woods. So what, I hear you ask does this have to do with clamps? Well, I try and make the hinges as close a fit as possible, which can put a big strain on the right angles at the bottom of the hinge mortise slots. A tenon that is even the slightest bit too fat or asymmetric will push apart the sides and make the wood of the handle or bowl crack.
I haven't had too much problem up till recently, as I've been using holly, maple and magnolia. I've been able to tap the hinges together with my hammer and the wood has behaved itself perfectly well, with no nasty cracks.
Then a friend gave me two large lumps of fresh box wood, and i have been busily converting it into spoons as fast as I can. Sadly I have had multiple failures, sometimes one after another, after another; always with the cracks starting at the base of the hinge slots. This has been depressing (to say the least), as it takes a fair amount of time and work to get to this stage, and besides, I don't like wasting box wood!
I wondered if it was something to do with the orientation of the billets I was using, whether the spoon is oriented radially or tangentally. (I'm going to try and identify this in the old spoons I have seen in the various museums here in Brittany and Marseilles, but that's another story).
I recalled that there are lots of examples of this type of crack in the old spoons I have seen in museums. These cracks usually seem to be the result of an opening strain on the sides of the hinges.
The spoon above shows this clearly. The person who made this spoon made a fatal mistake, in that he (it was probably a he!) tapered the hinge tenon slightly. This was something I have tried too, the hinge looks so much more graceful with a tapered tenon! You can clearly see that the end of the tenon is narrower that its base, and you can't miss the resulting crack in the box wood. I bet someone had a good swear when that happened. (Musée de Morlaix, no 2003.1.463)
This time the hinge pin is not exactly perpendicular to the long axis of the spoon, and has resulted in the handle moving off-centre when the spoon is folded. This is most clearly seen at the bowl-end of the spoon, where the handle can be seen to be to the right of the bowl. This of course has set-up an opening-force on the hinge mortice, particularly on the left side, which has split the box wood. This is only a tiny crack so perhaps it was the buyer, rather than the maker who did the swearing this time.
Then I realised that it was the relative lack of elasticity in the box wood that was making my hinges crack when I tapped them together. It was putting too much strain on the base of the slot and popping it open.
So here is the way I (think) I have solved this problem. Firstly I need to cut the hinges as accurately as I can in the first place and secondly, I use these tiny clamps that I bought at the second-hand tool stall at Spoonfest this summer, on the basis that you can never have too many clamps.
I THOUGHT they'd be useful, and I was right!!
I use one while I'm fitting the hinge (as in the top photo) and then I clamp the finished hinge until it has dried as yuo can see in these last two pictures. Problem solved.