ONE:To illustrate the practical application of what has preceded, let it be supposed, for example, that a machine is to be made for cutting teeth in iron racks ? in. pitch and 3 in. face, and that a design is to be prepared without reference to such machines as may already be in use for the purpose.
FORE:
FORE:A carriage moving on angular ways always moves steadily and easily, without play in any direction until lifted from its bearing, which rarely happens, and its lifting is easily opposed by adjustable gibs. A carriage on a flat shear is apt to have play in a horizontal direction because of the freedom which must exist to secure easy movement. In the case of tracks, it may also be mentioned that the weight of a carriage acts as a constant force to hold it steady, while with a flat shear the weight of a carriage is in a sense opposed to the ways, and has no useful effect in steadying or guiding. The rigidity and steadiness of tool movement is notoriously in favour of triangular tracks, so much so that nearly all American machine tool-makers construct lathes in this manner, although it adds no inconsiderable cost in fitting.
