Wood.—In the early days of machines wood was largely used in their construction, but it is now used to a very limited extent in that direction. Beech and hornbeam are used for the cogs of mortise wheels. Yellow pine is much used by pattern-makers. Box, a heavy, hard, yellow-coloured wood, is used for the sheaves of pulley blocks, and sometimes for bearings in machines. Lignum-vitæ is a very hard dark-coloured wood, and remarkable for its high specific gravity, being 11⁄3 times the weight of the same volume of water. This wood is much used for bearings of machines which are under water.
XVIII. MISCELLANEOUS EXERCISES.
The illustrations in this chapter are in most cases not drawn to scale; they are also in some parts incomplete, and in others some of the lines are purposely drawn wrong. The student must keep to the dimensions marked on the drawings, and where no sizes are given he must use his own judgment in proportioning the parts. All errors must be corrected, and any details required, but not shown completely in the illustrations, must be filled in.
Exercise 62: Single Riveted Butt Joint with Tee-iron Cover Strap.—Two views, one a side elevation and the other a sectional elevation, of a riveted joint are shown in fig. 60. Draw these views, and also a plan projected from one of them. Show the rivets completely in all the views. Scale 4 inches to a foot.
Fig. 60.
Fig. 61.