page8
page 44
Bamboo Journal
Italian Bamboo Rodmakers Association
Stated in a slightly different way, the beam edge
is straight to one mil (or better) over the length
of the guide carrying the luthier plane. And this
is all you care, as the luthier plane and the
carrying guide ride along the beam. The reverse
would be a disaster! If the beam would be
moved under a mill head, then one mil accuracy
would be required over the entire length! I
daresay that with metals, that is the only way to
go. But the price to pay is enormous in terms of
accuracy and overall tolerances.
I have decided to use quite a lot of space to
discuss this point because I believe it is a very
important one, and I noticed that people tend to
become dogmatic when it comes to accuracy
discussions.
Anyway, for those who still do not agree, I invite
them to re-read the Bible, where Garrison
grumbles about a bumpkin who used his
planing form as a crowbar to dislodge a large
stone in his backyard. As a consequence, the
bars were so curved he had to put a piece of
wood to stop them from rocking. Yet everyone
believed him when he said it was important to
try to work strips with a thousandth of accuracy
and he succeeded in doing so sometimes.
The chapter on the planing form contains
methods for checking the quality of the surfaces
with straight edges, the sensitivity being of the
order of one mil. Also, methods to measure the
dihedral between the beam faces to an accuracy
of one tenth of a degree.
While the surfaces are planed with the Veritas
low angle block plane, squareness between the
surfaces is obtained using a simple method.
Using again the Veritas plane and an assembly
to form a 90 degree fence (also shown in a
photo). A C clamp is used to fasten a wood
fence to one of the plane sidewings. In order to
inely tune the setting to 90 degrees, the edge of
the blade is very inely adjusted by acting on the
setscrews. While their use was primarily concei-
ved to guarantee against accidental changes of
the blade setting, they can also be used for the
ine tuning necessary for the setting to 90
degrees. The adjustments of the setscrews are
done by trial and error approach, as I have not
been able to ind a satisfactory method to check
directly the actual position of the blade setting.
Deviations from 90 degrees are checked on the
beam with a high quality, 3 micron accuracy
square.
I thank Dieter Schmid for advice on many items
I use, and his super fast and accurate service.
Finally, the chapter contains a discussion on the
choice of wood. Moss suggests hard and durable
woods. I suggest soft wood, nodeless, straight
iber ir. There are many reason for this choice,
including availability, it can be planed easily, the
planed surfaces are very smooth, and so on. But
there is also a more interesting reason.
A step back. The planing form bars are made in
steel because steel will not be damaged by the
plane. Bamboo strips will be planed until the
blade of the plane grazes the surface of the bars.
Once this happens, there is no danger that the
bamboo strip will be overplaned, being protec-
ted by the steel bars. Paradoxically, the choice of
making the former beam out of a wood that is
deinitely softer than the bamboo brings to the
same result. As it will be discussed later, this
will happen because the inal passages to
remove the last few mils from the bamboo strips
will be done with a scraper plane. I found that
when the bamboo strips protrude very little and
the blade protrusion is one or two mils only, the
scraper will at irst remove very thin shavings.
However, when the glued strips are lush with
the beam surface, the scraper plane will stop
working and remove no more material. This is
probably due to the fact that at low blade
protrusion ir is so soft that the blade just
displaces the ibers without cutting them. It is
probably like scraping felt. So the all important
inal passes with the scraper plane can be done
with great conidence. Again, I believe this is
one of the important ingredients in making the
revised method successful. I anticipate here that
the scraper plane that is best suitable is the 212
Lie Nielsen scraper plane, as discussed in the
last chapter. It is the only scraper plane using
very hard blades, a must when working
bamboo. Other companies offer somewhat
softer blades, as they advocate the technique of
forming a burr at the cutting edge. I thank
Deneb Puchalsky of LN for his kind competent
advice.
2. The curved pane
Another important innovation introduced by
the revised method is that the tracks planed
along the beam edges are curved, and the
radius of curvature matches the average curva-
ture of good quality bamboo culms, that is R=25
mm.