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Hook Angle
The size of the hook angle is a question of the type of wood
and the intended feed speed. The generally accepted rule is that softwoods
require a greater hook angle than hardwoods. On the other hand the smaller the
hook is the slower the cutting capacity of the machine will be. In practice it
is impossible to use too many different hook angles in one mill, so a correct
balance in the choice is necessary.
The object of the hook angle is for the teeth to
"hook" themselves into the timber remove a certain amount of material
so that the log is fed into the saw. If the hook angle is too small the log must
be forced into the saw blade in order to make the saw cut. This may create a
rubbing action that will wear the teeth faster and make them blunt. Side
deflections may be another effect.
The figure below shows some general recommendations. The
decision must be based on type of wood and feed speed.
Choice of Hook Angle
| Hook angle |
15 |
20 |
25 |
30 |
| Type of wood |
Hardwood
(high density) |
Hardwood
(medium to low density) |
Hardwood
(low density)Softwood |
Softwood |
| Feed speed |
<8 m/min. |
8-27m/min. |
27-46 m/min. |
>50 m/min. |
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