Transition comment

01. The broad matters discussed in chapter 1, namely those of freedom, mobility and the need for sufficient constraint in mechanism, are of great importance in the wide realm of practical machine design. They are derived however from a somewhat narrow set of assumptions regarding (a) rigidity in the absence of elasticity, (b) crookedness in the absence of accuracy, and (c) direct contact at joints in the absence of lubricated clearances. In chapter 1 there is thus developed what might be seen to be a somewhat simple theory of constraint. It is a simple theory; it is directly applicable; but only in a very rough way is it able to predict, for much of our ordinary machinery, the actual mechanical behaviour of the moving parts.

02. We often see in ordinary working machinery the unhappy effects of friction due to eccentricities of loading (§ 17.24), the consequent continuous likelihood of jamming, chatter, and wear, and the necessity for lavish lubrication at badly affected joints. Such phenomena will be evident whenever the kinematic design for a smooth transmission of the wrenches has been poor (§ 17.26), or, alternatively, whenever the jamming phenomena themselves have been an intended activity of the machine (§ 10.61). Although such matters are important and need to be studied, they are in a curious way irrelevant here. They are not the matters being implied at § 2.01.