A COMPACT RATCHET BRACE: Bill Steer describes the construction of a precision version of this simple tool, that once formed an essential part of every fitter's tool kit - Part I

摘要

A ratchet brace may seem to be a strange sort of tool to be describing in these pages. These implements tend to be regarded as something from a bygone age, more akin to the historical development of heavy engineering than the light, precision work that most of us are concerned with. It was perhaps for this reason that I had never really considered their potential value. That was, until I was faced with drilling and tapping a number of very awkwardly located 6BA holes in the chassis of a near completed 5in. gauge locomotive. For those unfamiliar with ratchet braces, they consist essentially of a means of holding a drill bit, which is then rotated by a lever operating through a ratchet. The cutting force is provided by means of an axially-mounted jacking screw, which works against a suitable abutment. Such braces were normally quite large, often crudely constructed and required a lot of skill and muscle power to operate. Figure 1 depicts a ratchet brace of a type available some 60-70 years ago. It is similar to one illustrated in an old Tyzack catalogue I have by me, which indicates that they could be bought in a variety of sizes, with lever arms ranging from 10 to 24in. length. Because of the erratic side thrusts involved and the high torque that could be applied they were often used in conjunction with stubby, taper shank drill bits.