Section 3 Units 5 and 6

Grit

Grain size; the measurement of the degree or coarseness of grinding wheel abrasives in which the lower the number, the coarser the wheel; grain sizes range from 8 to 600

twist drill

a common holemaking tool with spiral grooves in its body

glazing

a condition in which a grinding wheel cuts inefficiently because the grains of the wheel become dull more quickly than normal, preventing new, sharp grains from being exposed.

loading

a condition in which a grinding wheel or the teeth of a file cut inefficiently because pieces of soft metal become lodged in the wheel or file.

thread-cutting die

a cutting tool used to cut an external thread on the outside diameter of a workpiece

tap

a cutting tool used to produce internal threads

electric drill

a handheld holemaking tools used to power holemaking tools

ring test

a precautionary check to ensure a grinding wheel is not cracked by suspending the wheel by the center hold and lightly tapping with a non-metallic object

combination drill anf countersink (center drill)

a short drill used for spotting hole locations or for machining a recess to accept a lathe center, which has a small pilot drill on the tip, and transitions into a countersink with a 60-degree angle

tool reset

a small adjustable platform at the face of a pedestal or bench grinding wheel that aids in supporting work during offhand grinding

spot drill

a tool used to create a shallow cone-shaped hole to serve as a more positive starting point for a twist drill

spiral-flute tap

also cut threads and have a spiral flute much like the flutes on a twist drill

spiral-point (Gun) tap

also cut threads and have straight flutes with a special angle ground on their ends. the angle on the end serves to create stringy chips that are projected forward as the tap is in use.

nominal

an approximation of a desired or targeted size

adjustable reamers

are similar to expansion reamers, but they have a different construction, which allows a much greater range of adjustability

taper chamfer tap

are sometimes called started taps, since they may be used to start a tapped hole that will be finished with another tap. thread are 7-10 threads chamfered to make the tap easier to start into the hole.

external thread

can be cut on the outside diameter of a workpiece with a cutting tool

internal thread

can be produced in the inside diameter of a workpiece with a tool

hand tap

cut threads and have straight flutes from the tip toward the shank. these taps curl the chips tightly and break them into small pieces.

thread depth

depth of a single thread measured from the crest to the root.

Wheel dressers

device used to dress a grinding wheel to expose fresh, sharp abrasive grains

Wheel flanges

discs used between a grinding wheel and spindle nut of a grinding machine to evenly distribute clamping force when mounting the wheel to the spindle

lead

distance a thread will advance in one revolution

pitch

distance from a point on one thread to the same point on the adjustable thread. For inch series threads, the pitch may be calculated by dividing 1 by the TPI

thread forming tap

do not cut, but form threads by displacing material into the shape of the threads

ISO metric

established dimensional standards regarding form, size, tolerance, allowance, classification, and class of fit for the consistent interchange of metric parts.

tap extractor

fingers that slide down the flutes of the broken tap, allowing it to be reversed out of the hole with a tap wrench

unified thread standard

for inch series threads; has established the form (shape) and dimensional standards for the consistent interchange of threaded parts

expansion reamers

have slots cut into the body that allow the reamer to expand to the exact size needed when the adjusting screw in the end of the reamer is tightened

pitch diameter

imaginary diameter measured where the thickness of the thread and space within the groove are equal. the pitch diameter of a thread is responsible for the fit between two mating threads.

counterboring

increases the diameter of a hole to a certain depth in order to allow a screw head or nut to be positioned flush with or below the workpiece surface

hand reamer

intended to be driven by hand and are fitted with a square driving surface for mounting a wrench

major diameter

largest diameter of a thread

jobber's reamers

longer flutes and are useful when reaming deep holes.

threads per inch (TPI)

number of threads contained within 1 inch of the workpiece length. (inch series threads only)

countersinking

process of cutting a tapered opening in a hole so that a flathead screw can be installed flush with the workpiece surface.

reaming

process of finishing a hole to a precise size with a smooth finished surface.

spotfacing

process of machining a flat spot on a rough surface surrounding a hole opening so that bolts, nuts, and washers will be properly seated when tightened.

drilling

process of using a cylindrical rotating cutting tool that is sharpened on its end to create a hole

Blotter

round disc of heavy paper surrounding the center area of a grinding wheel

minor diameter

smallest diameter of a thread. this diameter is measured from the base of a thread on one side to the base of the thread on the opposite side

spark breaker

sometimes called a spark arrestor, a pedestal grinder device used to catch and control most of the sparks generated by grinding wheels and to keep them from contracting the operator's hand

thread

spiral groove made on a round external or internal diameter

flutes

spiral grooves in the sides of a cutting tool that create cutting edges and provide a pathway for chips to be removed from the cutting area

chamfer

the beveled edge of a hole that allows easier entry of pins, aids in starting taps, and reduces burrs on edges of a hole

reamers

the cutting tools used for finishing an existing drilled hole to a precise size with a smooth finsihed surface

percentage of thread

the full thread depth compared to a partial thread depth, which is used to gauge thread strength

silicon carbide

the grinding wheel abrasive type used for grinding carbide as well as nonferrous metals

aluminum oxide

the most common grinding wheel abrasive type, used for general-purpose grinding og ferrous metals

plug chamfer taps

the most general purpose of the three and they are either used by themselves or after a taper tap when it is necessary to thread deeper into a hole. have three to five threads chamfered

crest

the peak of one thread and creates the points where the major diameter is measured

tap drill

the recommended drill bit size for a hole prior to tapping

class of fit

the relationship of tightness or looseness between the sizes of two mating parts

national pipe thread (NPT)

threads tapered 3/4 inch per foot to help seal them as they tighten together; sized according to the nominal inside pipe diameter rather than the major thread diameter

coarse pitch

threads with larger spacing between threads (fewer TPI)

fine pitch

threads with smaller spacing between threads

t-handle tap wrench

typically used for smaller tap sizes and afford better feel and sensitivity for how much torque is being applied to help avoid breaking the tap

general-purpose reamers

used for finished holes to a particular size

taper pin reamers

used to create precise tapers within straight holes that allow them to receive tapered pins

die stocks

used to hold threading dies when cutting threads

bottoming chamfer taps

used when a hole in blind, since they can cut full threads nearly all the way to the bottom of a hole. these taps only chamfer the first one two holes

straight tap wrench

usually provide more leverage, which helps you to apply the higher torque needed for larger tap sizes

root

valley between threads and creates the points where the minor diameter is measured

thread series

various diameters and pitch combinations within a thread system defined as standard