202 Machine Drawing
dharm
d:\N-Design\Des14-1.pm5
replacement. The replacement is simplified by making the outside diameter of the bush,
precision location fit (h6). The bush can then be assembled manually without a press. The
renewable bush must be prevented from rotation and axial movement. This is accomplished by
the provision of a flat surface on the collar (Fig. 14.2b). The shoulder screw prevents the bush
from getting lifted with the cutting tool.
14.3.4.3 Slip Bushes
When a hole in the work piece requires two operations such as drilling and reaming, it is
necessary to use two different guide bushes for different tools. The hole is first drilled using a
bush having bore suitable for drill. After drilling, the drill bush is removed and a reaming bush
is used to guide the reamer. For mass production, quick change is accomplished by the provision
of slip bushes (Fig. 14.2c). There are many variations of slip bushes.
a-Press fit bushRetaining
screw Slip bushLiner bushR
to release
slip bushdrill rotationb-Renewable bush c-Slip bushFig. 14.2 Types of bushes1 4.3.4.4 Special Bushes
Some work pieces or operations require unusual types of bushes which may involve simple
modification of standard bushes. A twist drill tends to slide down inclines and curves; causing
bending and breakage of drill. This problem can be overcome by altering the shape of the drill
bush to provide better support and resistance against bending as shown in Fig. 14.3.
(a) (b)Fig. 14.3 Special bushes