Glossary of Brake Terms

TERM
DEFINITION
arbor
Shaft which extends from spindle of lathe to which adaptors and drums and rotors are mounted.
backing plate
A steel plate used to support the back side of a rotor or drum when using the Quick Chuck or Hubless Adaptors
bell clamp
A mounting accessory that is used to support both the front and back sides of a rotor or drum when using a centering cone to machine a rotor or drum.
boring bar
Bar which holds a single cutting insert and is used to cut drums.
brake bleeder
A device used to bleed the air out of a hydraulic brake system. Two methods are used: 1. pressure is used to push the air out or 2. a vacuum pulls the air out of the system.
brake squeal
Noise produced by vibration of brake pads against calipers. Usually due to improper surface finish on the rotor or no backing material on the pads which causes the pads to vibrate and create a squeal.
caliper
(1) Tool used to measure the diameter of drums.
(2) Hydraulic cylinder assembly which actuates brake pads in a disc brake system.
carbide inserts
Replaceable, indexable cutting tips which are made of carbide and are used to machine a rotor or drum. 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 rigidly enough, dull cutting tip. 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. See also silencer.
centering cone
A mounting accessory that is used to center hubless drums and rotors while machining.
composite rotor
A hubless rotor with a stamped steel center section and a cast steel outside. 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 bell clamps and a centering cone and hold the work piece more stable.
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 they 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 perpendicular to the surface to be cut (see illustration), 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.

positive rake

 

See rake angle. If the cutter face is inclined upward (see illustration), the tool has positive rake. 3 cutting tips per insert due to geometry. Can be used to reduce chatter on solid (non-vented) rotors.
quick chuck
A brake 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. Also called a three jaw chuck.
RA
Arithmetic mean roughness value or more commonly known as roughness average. The roughness average is determined by how large the peaks and valleys are in a surface. The lower the RA, the smoother the surface.
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 onto 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.
tip/tips
Replaceable carbide cutting tip designed for brake lathes to machine brake rotors or drums to a new surface finish.
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. Also called machining.
twin cutter
A precise assembly that has two micrometers, tool holders and cutting tips allowing the operator to simultaneously machine both sides of a rotor to the desired thickness.
ways
Machined bearing surfaces used on machining equipment. One surface is fixed and the other slides along it. Dovetail slides are common.
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