Agriculture Reference
In-Depth Information
To draw such a shallow rise to create the curved camber across the open-
ing would be impossible from a trammel or 'radius rod' as it's 'striking point'
would be far off. The method adopted was to use a length of specially-shaped
timber termed a 'camber slip', traditionally made from a length of mahogany
or oak, which would not shrink or twist, about 300 mm longer than the widest
opening expected and so convenient for all spans of arches. Richards (1901,
57-8), though writing later, gives an explanation of the camber slip and it use
(Figs 104-106):
The mode of obtaining the camber slip is as follows (an extreme case is given, as
being easier of illustration): Suppose the opening to be 3
0
, and the rise 1
to the
foot, then the camber slip 3
0
long would have a rise of 3
; take a rod 3
0
long,
measuring in width 1
, or, in other words, hav-
ing in the centre half the required rise; shoot this piece from the middle to the
two ends perfectly straight, thus forming two triangles, as it were, upon a common
base; call the centre B, and the two outside points A and C (Fig. 104)
at each end and in the middle 2½
Figure 104
Drawing of a camber
slip.
Then take a piece of board a little over 3
thick,
planed both sides, and one edge shot [planed true], draw a centre line upon the
face of it, and 18
0
long and 6½
wide by ½
each side of it draw two other lines; call the centre line E, and
the two outside lines D and F (Fig. 105).
Figure 105
Pins positioned on the
drawing board awaiting
application of camber
slip.
Upon the centre E, 6
up from the shot edge, drive in a pin, and upon D and F,
3
up from the shot edge, drive in other pins. Then take the first piece (fig. 153),
already prepared, and with a pencil held at the centre B, apply it to pin F; and
with A on the same piece pressed against the pin E, move the piece with the pen-
cil from F to E, describing half the curve (Fig. 106).
Figure 106
Camber
slip with pencil on
point B travelling across
the face of the board
controlled by the pins
to trace and scribe the
camber of the arch.
