Manual of Purpose-Made Woodworking Joinery

146 Geometry for curved joinery

Straight- top Tudor arched shape

Figure 8.7(d): First draw span AB and divide by 9.

Mark one- ninth of the span from A to give D, and

one- ninth from B to give E. With a protractor, or

a modern roofing- square with a degree facility (if

setting out full- size on a joinery rod), set up and mark

diagonal normal lines passing through D and E at 78°

to the springing line. With centre D, strike sector-

curve AF, and with centre E, strike curve BG. From

F and G, draw straight crown lines at 90° to the two

normal lines, to intersect at apex C.

Note that the position of the centres D and E can

be varied to achieve a different visual effect, as can

the angles of the normal lines at D and E, drawn here

Fixed method

Figure 8.7(b): This method is simpler and can be
used when the rise is not given, or is not critical
and the only known information is the span. First,
draw span AB and divide by four to give DEF.
Draw  vertical lines down from D and F. With D
as centre, transfer F to intersect the vertical line
to give G as a centre. With F as centre, transfer D
to intersect the other vertical line to give H as a
centre. Draw diagonal lines from H and G, extend-
ing through D and F on the springing line. To form
the arched shape, strike sector- curves AI from D,
IC from H, BJ from F and JC from G. Note that
because the four centres form a square below the
springing line, this setting out is also referred to as a
box- method Tudor shape.

DEF

G H

B

I J

C

A

Figure 8.7 (b) Tudor arched shape – fixed or box
method.

Depressed Tudor arched shape

Figure 8.7(c): First draw span AB and divide the
springing line by six to give DEFGH. Draw vertical
lines down from E and G. With centre D, transfer
H down to O, and with centre H, transfer D down
to O. Draw diagonal normal lines through DO and
HO, extending down to intersect the vertical lines
at K and L, and extending up past the springing line
to establish I and J. To form the arched shape, strike
sector- curves AI from D, IC from L, BJ from H and
JC from K. Note that division of the span can be
varied to achieve a different arched shape, as can the
angles of the normal lines at D and H, drawn here at
60°. For example, 75° would make the arched shape
more depressed.

KL

O

AD EFGBH

I J

C

Figure 8.7 (c) Depressed Tudor arched shape.

AD

F

C

G

EB

78º

90º 90º

78º

Figure 8.7 (d) Straight- top Tudor arched shape.