page7
page 43
Bamboo Journal
Italian Bamboo Rodmakers Association
Organisation of the
“Former Beam Method. Revisited”.
Briely, the booklet is divided into 6 chapters
that are roughly organised according to the
sequence of the various operative phases of the
method. An overview of the necessary equip-
ment is shown in the following photo.
1. The former beam.
Great care in preparing the former beam is
essential because the accuracy with which it is
worked largely determines the inal accuracy of
the section of the rod you will build. The situa-
tion is similar to that one faces when discussing
the accuracy needed for a planing form.
As my interest is mainly for quadrate rods, let
me say that the beam I will consider from now
on is a wood beam with a square crossection.
Everything I will describe however can be used
in connection with triangular beams, if intere-
sted in hexagonal rods. The advantage with
quadrates is that the beam has the simplest
shape to generate, and just one beam is enough
to make all the four strips needed for one
section. Sides of 35 to 40 millimetres are OK.
With this choice, you only need a block plane
with blades of 1 5/8”. I use the Veritas low angle
block plane, the only one (as far as I know) that
is equipped with two setscrews for the lateral
coninement of the blade at the throat. As we
will see, this feature is very useful. Beam
lengths from one metre twenty to one metre
ifty. For the three-piece rods, one metre will do
in most cases. A solution to consider if you have
little space at home!
I am sure that the idea to use a wooden beam
to build bamboo strips with accuracies close to
a thousandth of an inch will immediately raise
many doubts. Can you use a wood beam at all?
One or two mils is a really small, and one may
object that it would be impossible to select a
wood beam that it is straight to few mils over
one meter or so. And even assuming you ind
one, it will not be straight in a little time, becau-
se of changes of air humidity. That type of
accuracy can be guaranteed only by metal bars
and by using milling machines. But the question
is whether you need at all to have such tight
tolerances. The answer is that it depends on
how you use the wooden beam.
Let me expand this point. Suppose you take a
wooden beam as described above, one and a
half meter long, 40 mm square. No one would be
too surprised to see one using a block plane and
planing a thin, continuous shaving, as wide as
the beam, from end to end. And with little
practice, the shaving can be made real thin,
somewhere between one mil or two (search
videos on the web, and see people generating
continuous shavings below half a mil!!). That
shaving is there to tell you that the surface you
have generated is real nice. So nice, that over
any length the size of the block plane, the
surface is lat to one or two mils. And this
despite the fact that perhaps the bar is slightly
bent, let us say with a bow of a few millimetres.
So the question whether a wooden bar can be
used to work bamboo strips with tolerances of
thousandths of an inch is a badly formulated
question. And the answer is yes and no, it
depends on how you use it.
The revised method I will describe uses a very
short, luthier plane to plane the tracks. The
small plane sits on a guide that glides astride
the beam edges. The length of the plane and of
the guide is a couple of inches, much shorter
than the block plane six inches, which in turn is
much shorter than the sixty inch beam length.
In a nutshell, it is this hierarchy of lengths that
guarantees that ultimately the actual depth of
the planed tracks will be accurate to one mil.