of finishing teeth tr = RPT for the roughing teeth ts = RPT for the semi-finishing teeth tf = RPT for the finishing teeth Ls = Shank length LRP = Rear pilot length D1 = Diameter of the tooth tip D2 = Diameter of the tooth root D = Depth of a tooth (0.4P) L = Land (behind the cutting edge) (0.25P) R = Radius of the gullet (0.25P) α = Hook angle or rake angle γ = Back-off angle or clearance angle Lw = Length of the workpiece (not shown) The most important characteristic of a broach is the rise per tooth (RPT), which is how much material is removed by each tooth. The RPT varies for each section of the broach, which are the roughing section (tr), semi-finishing section (ts), and finishing section (tf). The roughing teeth remove most of the material so the number of roughing teeth required dictates how long the broach is. The semi-finishing teeth provide surface finish and the finishing teeth provide the final finishing. The finishing section's RPT (tf) is usually zero so that as the first finishing teeth wear the later ones continue the sizing function. For free-machining steels the RPT ranges from . For surface broaching the RPT is usually between and for diameter broaching is usually between . The exact value depends on many factors. If the cut is too big it will impart too much stress into the teeth and the workpiece; if the cut is too small the teeth rub instead of cutting. One way to increase the RPT while keeping the stresses down is with chip breakers. They are notches in the teeth designed to break the chip and decrease the overall amount of material being removed by any given tooth (see the drawing above). For broaching to be effective, the workpiece should have more material than the final dimension of the cut. The hook (α) angle is a parameter of the material being cut. For steel, it is between 15 and 20° and for cast iron it is between 6 and 8°. The back-off (γ) provides clearance for the teeth so that they don't rub on the workpiece; it is usually between 1 and 3°. When radially broaching workpieces that require a deep cut per tooth, such as forgings or castings, a rotor-cut or jump-cut design can be used; these broaches are also known as free