Form 4083T, 7/96

Glossary - Brake Terms

arbor: Shaft which extends from spindle of lathe to which adaptors and drums and rotors are mounted.
backing plate: Adaptor piece used with the three jaw chuck system.
boring bar: Bar which holds a single cutting insert and is used to cut drums.
brake squeal: Noise produced by vibration of brake pads against calipers. Usually due to improper surface finish on rotor.
caliper: (1) Tool used to measure the diameter of drums. (2) Hydraulic slave cylinder assembly which actuates brake pads in a disc brake system.
carbide inserts: Replaceable, indexable cutting tips which are made of carbide. Carbide is used for inserts because it is very wear resistant.
chatter: Unacceptable surface finish produced on drum or rotor. Usually has a herringbone appearance. Possible causes: spindle speed too high, no silencer used, workpiece not mounted rigid enough. A high-pitch, chattering sound will be produced during cut.
chatter band: Elastic band, sometimes with lead weights, that is stretched around the outside diameter of a drum or rotor to eliminate chatter.
centering cone: A mounting accessory that is used to center hubless drums and rotors.
clamp cup: A mounting accessory that is used to clamp hubless drums and rotors. A centering cone must be used with clamp cups.
composite rotor: A hubless rotor with a stamped steel center section. Typically very susceptible to chatter.
discard dimension: A maximum drum diameter or minimum rotor thickness. This value is cast into the drum or rotor. If the drum or rotor is at this dimension or beyond, it must be replaced.
feed rate: The rate at which cutting tips move across the face of the drum or rotor. Expressed in inches/revolution or inches/minute.
finish cut: The final cut taken on a drum or rotor. The purpose of this cut is to produce the desired surface finish. This is usually a light cut taken at a low feed rate.
gib: A piece of material installed in machine slides that can be adjusted to compensate for wear.
hubbed drum: A drum that contains bearing races.
hubbed rotor: A rotor that contains bearing races.
hubless adaptor: A mounting accessory that is used to mount hubless rotors. Can be faster to use than clamp cups and a centering cone.
hubless drum: A drum that does not contain bearing races.
hubless rotor: A rotor that does not contain bearing races.
inserts: Replaceable, indexable cutting tips.
insert holder: Device that holds the cutting inserts. Three are required: left side of rotor, right side of rotor, and drum.
locking taper: A taper machined onto two mating parts such that when the parts are mated the frictional forces are so great will not rotate or move with respect to one another. No clamping forces are required to keep the parts joined, but considerable force is required to separate the items. This is an extremely rigid and accurate method of joining arbors and spindles. The included angle in a locking taper is typically between 2 and 3 degrees.
machine-to-dimension: The maximum drum diameter or minimum rotor thickness that may be achieved after cutting. This dimension is set to allow some material to wear before discard dimension is reached.
micrometer: Tool used to measure the thickness of rotors.
micro-finish: Surface finish measured in fine units, such as micro-inches.
micro-inch: One micro-inch=one millionth of an inch or 0.000001 inch.
negative rake: See rake angle. If the cutter face is angled downward, the tool has negative rake. 6 cutting tips per insert. A negative rake insert is more durable than a positive rake insert. This will provide longer insert life when cutting items of uneven and inconsistent hardness such as used drums and rotors.
non-directional finish: A finish applied to rotors with an abrasive disc after they have been cut. Used to reduce chance of brake squeal.
one-cut operation: The method of cutting a drum or rotor where a single cut is all that is used to remove heavy material and provide the desired finish. This is a deep cut taken at a slow feed rate.
positive rake: See rake angle. If the cutter face is inclined upward, the tool has positive rake. 3 cutting tips per insert due to geometry. Can be used to reduce chatter on solid (non-vented) rotors.
rake angle: The angle of the cutter face relative to horizontal.
rotor truer: Assembly which holds two cutting inserts and is used to cut both sides of a rotor at once.
rough cut: A cut taken on a drum or rotor for the purpose of removing large amounts of material without concern for resulting surface finish. This cut is taken at the highest possible feed rate. A rough cut is always followed by a finish cut.
silencer: A device used to eliminate chatter.
split collet: A mounting accessory that is used with hubbed drums and rotors. This device contacts the bearing races and provides both centering and clamping. A collet tightens onto the arbor and provides better centering than a taper adaptor.
spindle: The driven rotating member of a brake lathe. The arbors and attachments are installed into the end of the spindle.
spindle speed: The rate at which the spindle is turning. Expressed in RPM. Must always be set according to workpiece diameter.
stabilizer: A device used to eliminate chatter.
surface finish: Measurement of texture of drum or rotor after cut. Expressed in microinches.
surface roughness: Same as surface finish.
swirl finish: Same as non-directional finish.
taper adaptor: A mounting accessory that is used with hubbed drums and rotors. This device contacts the bearing races and provides both centering and clamping.
three jaw chuck: Abrake lathe adaptor used to hold hubless and composite drums and rotors. Superior to cones in terms of centering accuracy and repeatability. Operates on the same principles as the chucks used in industrial machine shop environments.
tool holder: Device that holds the cutting inserts. Three are required: left side of rotor, right side of rotor, and drum.
turning: Typically the machining process where the workpiece is rotating and the cutting tool is held fixed as it moves across the workpiece.
twin cutter: A more common term for rotor truer.
ways: Machined bearing surfaces used on machining equipment. One surface is fixed and the other slides along it. Dovetail slides are common.