Operation; Kinds Of Warp; Planing To Desired Thickness - Powermatic PM15 Operating Instructions And Parts Manual

Operation

Kinds of Warp

Warp is a variation from a plane or true surface.
Warping of wood is caused by uneven
shrinkage during the drying process. Shrinkage
is not the same in all directions of the grain and
due to the different grain direction in pieces of
lumber, different types of warpage can occur.
Cup or warped across width
With a board that is cupped you would first
plane the top flat and then turn the board over
and plane the bottom flat. See Figure 19. If
possible, ripping the board down the middle of
the cup would eliminate a large amount of waste
in planing to thickness.
Bow or warped lengthwise
The feed rollers on a thickness planer are going
to flatten a bowed board down against the
planer bed and thickness plane the board as if it
had little or no warpage. Then after the board is
removed from the planer it will be planed to
thickness but still have its original bow. See
Figure 20. The only way to remove the bow from
a board is to joint the board flat on one side on a
jointer. Then the board can be thickness planed.
Twist or twisted lengthwise
Twisted lumber is the most difficult warpage to
plane to thickness. In some cases the twisting is
so great that planing to thickness is impossible.
In this case you might saw the board into
smaller pieces and see if planing to thickness
can be achieved.

Planing to Desired Thickness

Thickness planing is the sizing of material to a
desired thickness, while creating a smooth
surface parallel to the opposite side of the
board. See Figure 21.
The art of thickness planing consists mainly of
using good judgment about the depth of cut in
various situations. You must take into account
not only the width of the stock, but the hardness
of the board, its dampness, straightness, grain
direction, and grain structure.
The effects of these factors upon the quality of
the finished work can only be learned through
experience. It is always advisable, whenever
working with a new type board, or one with
unusual problems, to make test cuts on scrap
material if possible prior to working on your
finished product.
Figure 19
Figure 20
Figure 21
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