The only interchangeable automatically opening die for turret lathes.
The only die for which each chaser is separately milled by a large free cutting mill.
The only lead controlling die.
The only chaser in which there is an error of only one hardening.
N the original development of the Turret Lathe for accurate lathe work, the greatest obstacle to our progress was the means formerly employed for cutting and measuring screws.
Die-cut threads were never correct in lead, and seldom of good shape. Lathe-cut or chased threads were found to have an error in lead averaging one-thirty-second of an inch in twelve inches when cut by new lathes, and much greater error when produced by old lathes. On account of errors in lead and shape, neither the die nor lathe-cut screws could be measured.
The so-called screw gauge used would tell how a screw would "feel" in a hole of the same length as the gauge, but would never tell how it fitted.
The die described has a lead error of less than one-sixty-fourth in eighteen inches; produces a shape of thread accurate beyond measure, making it possible for the first time to measure screw threads by the use of the ordinary micrometer, ring or snap gauge. We believe this marks a most important step in the advancement of accurate machine construction. A full explanation follows, making very clear how such results are obtained.