[Ansteorra-archery] Bowyerthon materials Part 3: Tillering
Sylvrfalcn at aol.com
Sat Apr 2 05:39:02 PST 2005
You've heard the term "tillering" in regards to bowmaking, but may not
understand exactly what it means. Tillering is the process of gradually removing
small amounts of material from the bow's limbs to even out or "balance" the
bend of the bow. It's a little more involved than just ensuring both limbs bend
the same, you also have to see to it that the limbs are bending gradually
enough to properly distribute bending stress, that way too much stress doesn't
build up in too small an area.
Here's an example of what I'm talking about; If you take two green sticks
of the same diameter, one short, and one long, you'll find it much easier to
break the short one than it is to break the long one. The same amount of force
that breaks the short stick will only cause the long one to bend. No matter how
long the limbs of your bow are, if you tiller in such a way that one small
area of the limb does all the bending, you just turned it into a "short stick",
by concentrating the stress load into that area. Now you understand why it's
important to have the limbs bend gradually.
It gets even more complicated when you start deciding if you're going to
make a working handle bow, or a non-working handle. A working handle bow is one
that flexes through it's entire length, including the portion that runs
through the handle. In a non-working handle bow, the center, or handle, section is
rigid, and does not bend at all. Obviously, the approach to tillering the two
styles is very different, and is more than I have room to cover here. But it
highlights my point that tillering is more than just getting both limbs to bend
the same amount.
So what do you use to tiller a bow? Scrapers are the most common tool for
gradually removing controlled amounts of wood from the limbs. A knife can be
used as a scraper, so can cabinet scrapers, et cetera. Rudder bows sells an
inexpensive scraper designed specifically for the job. I use a home made scraper I
made from a big old metal cutting file. It gives a two handed grip like a
drawknife, and with it I can produce an impressive pile of woodshavings lickety
So how do you tiller? You always remove wood from the belly side only.
During the rough shaping of the bow, it's important to make sure that the back
(front side) of the bow is perfectly flat and as smooth as possible. Any wood
removed after that, as in tillering, is taken off the belly side only. Tillering
takes patience, because you're removing small amounts of wood at a time, and
constantly checking and re-checking your progress on the tillering jig.
Tillering jig? Yup, it's a fixture you place the bow on to "draw" the bow
just enough to check the tiller. To do this you use a "tillering string" that's
much longer than your finished bowstring. The whole point with a tillering
string is to not have to bend the bow much, if at all, to get the string on.
There are notches on the tillering jig to hold the string at different "draw
lengths", so you can step back and look at how the limbs are bending. I can't
stress enough how important it is to not draw an unfinished bow any further than
you have to while working on it. If the tiller's way off, and you draw it too
far, you WILL damage the bow. Don't worry about going out and making a
tillering jig if you're coming to my class, we'll have tillering jigs and tillering
strings ready for you.
More to come, cheers for now,
Robert of Yorkshire
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