What is a "keyseater"? This simple, ingenious - and still widely-used compact machine - is intended to cut both internal and external keyways - either simple, straight-sided ones or, with the correct tooling, a variety of multiple slots of any profile desired, providing that a cutting tool can be ground to the desired shape. The machine consists of a heavy, cast-iron base holding the moor and drive mechanism with, at the top, a flat table with various kinds of T-slots and clamps to secure the work. In the case of the sophisticated Frömag type, at its centre is a tall, hollow guide column inside which runs a reciprocating cutter located at both top and bottom to ensure the most accurate cut. Some other, simpler types of keyseater from different makers, have their cutter exposed, held at the bottom but supported at the top by a simple adjustable thrust bar. With the workpiece located in position by clamps, alignment guides (and sometimes eccentric bushes) and the necessary settings made, the cutting tool, more usually a relatively inexpensive single-point type (not an expensive, difficult-to-sharpen long broach) is pulled downwards on its cutting stroke and lifted free on the upward. The work is cut in stages, each additional depth of cut usually applied automatically and, of course, adjusted in depth as necessary to cope with the particular job.
Both mechanical and hydraulic keyseaters are made, the advantage of the latter being that the cutter pulling force can be altered, via valve settings, to suit the size of cutter, dimensions of the slot and the particular material being machined. In addition, with a maximum load set, should the cutter hit a hard spot it will automatically stop and prevent tool breakage. On mechanical machines the tool lift is often by a cam or friction mechanism, the efficiency of the latter liable to be affected by the presence of oil and cutting fluid. On hydraulic models the feed to the cutter and its lift on the return stroke is controlled hydraulically - any lubricant thus having no dilatory effect.
With a tilting table fitted, tapered slots can be cut and, when equipped with an indexing plate (typically with 120 division) various multiple slots and splines also generated. Some models of keyseater, with the correct accessories and cutter bars, can also function as a broaching machine - those these, generally, have to be ordered with factory-fitted modifications.
Keyseaters have been made where the cutter remains stationary and the table moves up and down, but these are rare and limited to handling lighter jobs - a table able to lift several tons in a reciprocating manner might give a designer food for thought...
All keyseaters, no matter what their work capacity, are remarkably compact with the two types, mechanical and hydraulic aimed at different markets. While the relatively simple and less-expensive mechanically-driven ones might be employed in an ordinary workshop and used to do one-off jobs or simple production runs, hydraulic models are more suited to continuous production work. Not only do the hydraulics allow the various settings be just "dialled in" to suit different jobs, they are more easily arranged to take "ganged-up" workpieces - a set of pulleys for example, stacked one on top of another - and have the safety feature of automatic cut-out when overloaded. Some, intended for really heavy work, have been advertised as able to mount jobs weighing over 25 tons and cut keyways up to eight inches wide and over 80 inches long.
From the catalogue extracts below, a full picture can be obtained of how typically modern mechanical and hydraulically-operated keyseaters - in this case from the German Frömag range built circa the 1940s to the 1970s - are constructed and operated.
The writer was amused to see, in a local CNC machine shop, that each of the three cells also had a single, manually-operated machine, not a keyseater but, as the work was simple, a Butler slotter from the 1950s for the sole purpose of machining keyways.
Still manufactured, Frömag keyseaters can be obtained from http://mittsandmerrill.com/the-machines.html