Signedface, top slide, left: BARTH'S CLASSIFICATION SLIDE RULE / FOR / CARBON STEELS.
Inscribedface, top slide, right: V = (CONSTANT)({1-[7/(10+E)]}/{S-30,000})
FunctionFor determining the standard cutting speed, and corresponding hardness class number, of carbon steels.
The user first moves the second slide to left or right such that the appropriate value on the elongation scale (top slide) coincides with the appropriate value on the tensile strength scale (second slide, top edge).
Holding the second slide in place, he locates the value on the cutting speed scale (bottom slide) that coincides with the 100% arrow on the unlabeled scale (second slide, bottom edge). This indicates the standard cutting speed for the material in question. (If, due to the position of the second slide, the 100% arrow falls outside the cutting speed scale, the user reads off one of the other hash marks on the unlabeled scale [second slide, bottom edge], then transforms the velocity accordingly. For example, if he reads V = 20' off the 160% mark, the standard cutting speed is 20'/1.6 = 12.5'.)
The hardness class number is that value on the bottom scale of the third slide which comes closest to coinciding with the standard cutting speed, as determined by the above operation.
Historical AttributesThis is part of a set of slide rules for machine shops designed by Carl G. Barth under Frederick Winslow Taylor's system of scientific management. Given the characteristics of a particular machine and a depth of cut, for example, a shop manager could quickly calculate the most efficient speed and feed settings using one of Barth's speed and feed slide rules. Other objects in the collection include slide rules for helical springs, belts, and gears, as well as jigs for making slide rules.
Primary SourcesCarl G. Barth, "Slide Rules for the Machine Shop as a Part of the Taylor System of Management," Transactions of the American Society of Mechanical Engineers 25 (1904): 49-62.
Frederick W. Taylor, "On the Art of Cutting Metals," Transactions of the American Society of Mechanical Engineers 28 (1908): 31-432.
ProvenanceThe papers and slide rules of Carl G. Barth and his son, J. Christian Barth, were transferred to the Baker Library of the Harvard Business School by J. Christian Barth in 1961.
The slide rules were transferred from Harvard Business School to the Collection of Historical Instruments in 1980.