388 Machine Drawing
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d:\N-Design\Des19-1.pm5
19.4.6 Castor Wheel
Castor wheels are used on trolleys for moving them in any direction with minimum effort. A
castor assembly is shown in Fig. 19.22. It consists of a frame 1 made of cast iron. The frame is
freely suspended from the plate 2 by king-pin 8 and nut 9. The assembly is kept intact by a split-
pin. The brass bush 6 is pressed into the hub 3. The rubber tyre 5 is placed on the hub and kept
in position by the two flanges 4 which are clamped by bolts 10. This wheel assembly is located in
the frame by the shaft 7. The shaft is positioned with a nut and a split-pin. A grease nipple is fixed
on the head of the shaft, to provide lubrication between the shaft and bush bearing.
19.4.7 Speed Reducer
Gear trains are used for transmitting power and also to change the speeds between two or more
shafts. Figure 19.23 shows a speed reducer in which bevel gears and spur gear trains are used to
obtain speed reduction. It consists of the gear box body 1 to which is fixed the end support 2. The
spur gear 7 is fixed on the shaft 3 along with the roller bearings 12 and 13. The driven gear 6 is
then keyed in position.
The bevel gear 9 and spur gear 8 are mounted on the shaft 4 along with the bearings at the
ends. The bevel gear 10 is mounted on the shaft 5 along with the bearings. The driver pulley 11 is
fixed with a key on this shaft. The speed reduction takes place in two stages between the bevel
gears 10 and 9 and between spur gears 8 and 7.
The bearings are provided with bearing covers 15, oil seals 14, bearing retainer 16, and
circlips wherever necessary. Eight tapped holes of M8 and free holes of φ 8 are provided on the body
to fix the cover. The holes of φ 6 are made in the body for dowel pin location.
Exercise
The assembly drawing of a speed reducer is shown in Fig. 19.23. Draw the details of the following,
to suitable scale:
(i) End support 2, (ii) Shaft 4, (iii) Spur gear 7, (iv) Bevel gear 9, and (v) Bearing cover 15.
