but it is possible to achieve a range of . Surface broaches' range is usually , although the feasible range is . Tolerances are usually ±0.002 in (±0.05 mm), but in precise applications a tolerance of ±0.0005 in (±0.01 mm) can be held. Surface finishes are usually between 16 and 63 microinches (μin), but can range from 8 to 125 μin. There may be small burrs on the exit side of the cut. Broaching works best on softer materials, such as brass, bronze, copper alloys, aluminium, graphite, hard rubbers, wood, composites, and plastic. However, it still has a good machinability rating on mild steels and free machining steels. When broaching, the machinability rating is closely related to the hardness of the material. For steels the ideal hardness range is between 16 and 24 Rockwell C (HRC); a hardness greater than HRC 35 will dull the broach quickly. Broaching is more difficult on harder materials, stainless steel and titanium, but is still possible. Types Broaches can be categorized by many means: Use: internal, or surface Purpose: single, or combination Motion: push, pull, or stationary Construction: solid, built-up, hollow or shell Function: roughing, sizing, or burnishing If the broach is large enough the costs can be reduced by using a built-up or modular construction. This involves producing the broach in pieces and assembling it. If any portion wears out only that section has to be replaced, instead of the entire broach. Most broaches are made from high speed steel (HSS) or an alloy steel; titanium nitride (TiN) coatings are common on HSS to prolong life. Except when broaching cast iron, tungsten carbide is rarely used as a tooth material because the cutting edge will crack on the first pass. Surface broaches The slab broach is the simplest surface broach. It is a general purpose tool for cutting flat surfaces. Slot broaches (G & H) are for cutting slots of various dimensions at high production rates. Slot broaching is much quicker than milling when more than one slot needs to be machined, because multiple broaches can be run through the part at the same time on the same broaching machine. Contour broaches are designed to cut concave, convex, cam, contoured, and irregular shaped surfaces. Pot broaches are cut the inverse of an internal broach; they cut the outside diameter of a cylindrical workpiece. They are named after the pot looking fixture in which