Page:The Kinematics of Machinery.djvu/469

 PLUMMER-BLOCKS. 447

couplings we have partly pairs of elements and partly complete mechanisms or portions of them, and that it is possible for the

FIG 303.

individual links of the latter themselves to consist of several pieces united by screwed or keyed joints.

Plummer Blocks, Bedplates, Brackets and Framing.

The plumrner-block or pedestal makes, along with the spindle or shaft C +, the pair of elements C+ C~ ; it is therefore itself the single kinematic element G~. In its actual construction many varieties of screwed and keyed joints and other such auxiliary mechanisms are used, partly to unite the separate pieces of which it consists (i.e. to form links), and partly to facilitate lubrication and cleaning. In neither case therefore do they appear in its (principal) kinematic formula.

In the bed-plate which carries the plummer-blocks we have simply the fixed link or frame of a kinematic chain, arranged so that the elements C~ or C+ may be connected to it by suitable fastenings, or made in one piece with it. Fig. 304 shows a bed- plate for the two parallel shafts A and B. If we imagine the two plummer-blocks to be in their places, we have in the whole simply the constructive form of the frame C~...\\... C~ t Fig. 305.

A bed-plate for two shafts at right angles to each other, Fig. 306, such as is frequently required for turbines, is (with its two plummer- blocks) equivalent kinematically to the frame, C f -...JL...C r ~ in