centauro SP 400, Use And Maintenance Manual, Page: 16 / 50

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4) Perfect initial and subsequent sharpening
Sharpening must be done as soon as the teeth lose their cutting edge and
the blade starts forcing the cut.
It can be done, especially for teething with a short pitch, with a triangle file.
In this case the triangle, whether by hand or machine, must have round edges,
to join the bottom of the teeth well and to prevent the start of cracking
(fig. 15-3). When using emery grinding wheel sharpeners it is absolutely
necessary to prevent the bottom of the teeth from heating up to a yellow or
blue colour, which easily happens when not paying the due attention to using
these machines. Overheating the teeth causes a self-hardening action and
consequently a change in the structure of the steel that becomes hard like
glass, with the consequence of inevitable cracking and breakage of the
blades. In addition, the emery grinding wheels have often to be dressed with
special equipment and the edge must be kept adequately round to the extent
of the bottom of the tooth that has to be sharpened. It is generally advised to
use number 60 for the grain of the emery grinding wheel.
Fig. 15-1 Tooth bending Fig. 15-2 Tooth bending
Fig. 15-3 Tooth bottom
2) Appropriate toothing for the work to be carried out
The shape of the tooth should be chosen in relation to the type of wood to be cut:
Ordinary toothing is suitable for dry and seasoned woods, spaced toothing is suitable for soft, green or fibrous and
even resinous woods, the gullet tooth is better if you have a sharpener suitable for sharpening this type of tooth.
The pitch of the tooth should be chosen in relation to the type of wood and to the cutting height to be made: for dry
woods and low cuts, short pitches, for green woods and high cuts, long pitches.
In other words, the empty space of the tooth must be able to discharge all the sawdust its cutting edge produces.
3) Exact setting of the teeth
The teeth must be set carefully and precisely. The teeth must never be bent down to the base because this causes
the blades to crack. The teeth must be set so that the bending should not go over half their height and their side
deviation (for each tooth) the blade thickness (figs. 15-1, 15-2).
Example: a blade of thickness 0.90 mm must have a maximum overall setting of 1.80 mm. It is necessary to observe
that the maximum setting may be suitable for very green woods, whereas for seasoned woods an overall setting of
roughly one and a half times the thickness of the blade is to be preferred. Example: thickness 0.90 mm., setting
1.35 mm.
Moreover, those who wish to leave the tooth neutral for discharging the sawdust (as normally occurs for soft, green
and resinous woods) have to proceed as follows:
set a right-hand tooth, a left-hand one, then leave a straight tooth and so on. All other methods are wrong. With
pitches over 25 mm it is better to leave one neutral tooth every four teeth.