Manual of Purpose-Made Woodworking Joinery

Shrinkage distortion 5

at 1.2(d). Four different conversions of the basic
quarter- sawn shape are illustrated in Figures 1.2(e)
(f )(g).

Rift or radial sawn

Figure 1.2(e): This method of converting the quarter-
sawn log (as can be seen in the illustration) is the least
economical method of conversion, because it leaves
wasteful wedge- shaped pieces; but it is the best way of
displaying the medullary rays as a feature on the faces
of certain species of hardwood boards. Also, most

importantly, because the annual growth rings are at
right angles to the face of the boards (as illustrated at
1.2(d) above) there is less shrinkage across the boards’
width, less warping and no cupping.

Quarter sawn variations

Figure 1.2(f ): As illustrated in these three quadrants
(quarter- sawn shapes), less wasteful arrangements are
used, producing some boards with annual growth rings
at right- angles to the face of the boards and a remain-
der with growth rings that are within an acceptable
angle of not less than 45° to the face of the boards.

Tangential sawn

Figure 1.2(g): As illustrated, after the log is sawn
into quarters, boards can also be produced with
their faces tangential to the annual growth rings.
This is another economical form of conversion with
minimum waste, which can display the growth rings
figuratively on the face of boards from such species
as pitch pine, etc, but – as mentioned previously –
tangentially sawn boards are extremely susceptible to
unequal shrinkage and a form of distortion known as
cupping.

SHRINKAGE DISTORTION

Figure 1.2(h): Converted timber is subject to distor-

tion through unequal shrinkage and it shrinks mostly

in the direction of the annual rings (known as tangen-

tial shrinkage) – and it shrinks to a greater extent in

the sapwood than the heartwood. The likely distortion

this can cause is illustrated below. Note that the two

concave/convex shapes are known as cupping – and

the shrinkage effect on the square section shown on

the right- hand side of the log is known as diamonding.

With this knowledge, we can study the end grain of

any piece of timber and visualize its likely distortion

by knowing that the longest annual rings will shrink

the most. On tangential- sawn boards, this shrinkage

causes cupping.

Figure 1.2 (f) Three less wasteful quarter- sawn variations

(shown reassembled).

Figure 1.2 (e) Rift- or Radial- sawn log quadrant (shown
reassembled).

(e)

(f)

Figure 1.2 (g) Tangentially sawn quarter- log.

(g)