Page 111 - Industrial Cutting of Textile Materials

98 Industrial Cutting of Textile Materials

Round knife
Fabric plies

Fig. 7.20 Movement of a round knife during cutting.

Straight knife Straight knife

Fabric plies

Table surface
(A) (B)
Fig. 7.21 Movement of a straight knife downwards (A) and upwards and (B) during cutting.

The blade of a straight-knife machine oscillates during the cutting process. During
its upward movement, friction loosens the fabric plies and promotes their mutual dis-
placement (see Fig. 7.21B). For this reason, a presser foot must be used. This com-
presses the fabric plies and prevents them from moving upwards with the knife.

7.4.4 The ease of transfer of a cutting machine or parts
of a spread
Movable cutting machines are easily transportable because of their baseplates that
are placed on independently moving rollers. The baseplate must be set as low as
possible to ensure the minimum deformation of fabric plies in a spread (see Fig. 7.22).
However, more powerful and heavier cutting machines need larger, stable baseplates.
The baseplates also have to be higher to accommodate the large rollers. This increase
in the weight of a machine and the size and height of a baseplate makes large movable
cutting machines less manoeuvrable and accurate than smaller machines.
A band-knife machine carries out the cutting process by moving the material whilst
remaining stationary. These machines are therefore used to cut the medium and small
parts of a spread. The smaller the cut spread parts are, the easier and more precisely
the components will be cut. For increased ease of movement, the surface of a band-
knife machine may be equipped with a special blower system that decreases resistance
between fabric plies and the table surface (see Fig. 7.23).

7.4.5 Permissible tolerances in the original contours
of pattern pieces

Taking into account the previously described factors influencing the precision of the
manual cutting process, certain tolerances from the original contours of pattern pieces
are permissible (see Table 7.1).