page13
page 49
Bamboo Journal
Italian Bamboo Rodmakers Association
4. How to plane grooves according to a
chosen taper. The shim packs method. The
Shim Pack Master.
The guide and luthier plane generates a ixed
depth groove, as we have repeatedly said (the
actual depth being eventually adjusted with the
shims inside the guide). Obviously, this does not
suit us, as we need to plane grooves with depths
changing according to the taper we have chosen.
To build a butt for example, we want the depth
of the track to reduce from the maximum depth
of the butt section to the depth at the ferrule
station. The method to achieve this result is
very simple and it consists in fooling the guide.
The deception involves positioning on the sides
of the beam a series of shims in a staircase
fashion so that the guide and the plane go up or
down as we desire. For example, for a butt
section, we want the guide to be at his highest
point when at the ferrule station, and be at the
lowest at the wood insert. The guide will keep
thinking it has planed a constant depth groove
but actually, at any position along the former
beam, this “constant” value will be the sum of
the depth actually planed away and of the
shifting up due to the shims. Consequently, at
the station of the ferrule there is the largest
number of shims and it will decrease to zero at
the wood insert station.
Also, one single shim gives an upward shift, but
also an equal shift left or right, depending on
which side the shim is. But we are only intere-
sted in the shift upwards and we do not want to
introduce lateral shifts of the plane at all. So the
shims are equally into two separate packs. They
will sit onto the two beam sides. At worst, they
will differ by one shim alone.
To put this scheme into practice I searched the
best way to generate the shim packs, using
various materials and a fair number of glues. It
was a frustrating phase, with disappointing
results. Lack of uniformity of the shims thick-
ness, variations due to the non-uniformity of the
glue, packs of shims too rigid to it well on the
sides of the bar, variations of thickness with
time, brittleness, etcetera.
At the end, I found a solution I think it is hard to
beat with regard to precision, stability and
easiness of use. In honesty, I am kind of proud I
have found this scheme, and I hope you will like
it too. A comment. Every time you give a
dimensional speciication, the iner it is, the
more expensive the object will be and it will also
be more dificult to ind. Example. If you look for
a straight edge with one mil accuracy over ten
inches, you will likely ind it in a hardware shop
not too far. But if you look for 0.1 mil accuracy
over the same length, then you must go to very
specialized places, and will cost you substantial-
ly more. Do you need 0.1 mil accuracy? Not for
thickening bamboo strips, for sure. But thinking
to shim packs, say twenty or thirty layers…..then
0.1mil accuracy and stability becomes
something desirable indeed. I felt at loss.
But then I found the ideal solution while idly
looking at the specs of 3M adhesive tape I had at
home, the 810 tape called “Magic”, the transpa-
rent one with the matt back, on which one can
write. The thickness of the tape is given to 2.2
thousandths of an inch. Eye-popping!!! Guaran-
teed with 0.1 thousandths of an inch precision,
…….. about three microns…….. and it can be
found anywhere!!!!
If you do the calculations, one layer alone on a
beam side at 45 degrees introduces an upward
shift of exactly 1,5 thousandths of an inch. The
ideal to form the steps of the staircase. Added
advantages. It is already in the shape of tape of
the right width (3/4”), it has adhesive on one
side, it can be easily stuck one layer to the other;
the glue between the two layers is stable in
time; it keeps an admirable lexibility and rests
wells on the sides of the bar. The perfect choice!
I suggest building the steps on a strong ¾”
plastic ribbon made with oriented ibers, the
kind used in gift parcels, so that the shim
packets can be placed and removed, used many
times and kept in a small library of tapers. A lot
faster than re-adjusting a planing form!