Holemaking on the Manual Mill 271

adjustable boring head

A toolholder used in boring operations that require a hole diameter larger than that of the tool. An adjustable boring head can be set to bore differently sized hole diameters.

bore gage

A hole inspection gage that makes three points of contact within the hole. Bore gages are handheld, variable instruments that provide very accurate readings of hole sizes.

boring

The process of enlarging an existing hole with a single-point tool. Boring removes small amounts of material to achieve tight tolerances and finishes.

boring tool

A long bar used to position a single-point tool for boring operations. Boring enlarges existing workpiece holes.

center drill

A type of drill with a wide shank and a 60° angle tip. The center drill is used to start a hole to ensure that the hole is machined in the right location.

center hole

A shallow hole used to locate other holemaking operations. Center holes are created with center drills.

chamfer

A process that adds a small, angled surface on the end of a shaft, around the opening of a hole, or along an edge. Chamfering removes the sharp edge and helps remove burrs.

chamfer tool

A tool that creates an angled surface which eliminates a sharp corner on a workpiece. Chamfer tools are available in a range of angles.

chips

A piece of metal that is removed form a workpiece during cutting or grinding. Chips are tiny curls, shards, fragments, shavings, or particles of metal.

collet

A split-sleeve device that expands or contracts to hold a cutting tool or workpiece in place as it rotates. Collets are designed to hold specific dimensions.

concentric

Having a common center or sharing the same axis with another object. Concentric objects are generally circular or cylindrical.

conical

Cone-shaped. Conical workpiece features gradually change from a larger diameter to a smaller diameter.

counterboring

An operation that enlarges the end of a drilled hole to allow room for a head of a screw or nut. Counterboring produces an enlarged opening with a flat interior and square shoulder

counterboring

An operation that enlarges the end of a drilled hole to allow room for a head of a screw or nut. Counterboring produces an enlarged opening with a flat interior and square shoulder.

countersinking

An operation that cuts a conical surface into a hole. Countersinking allows the head of a screw with a matching conical angle to rest flush with the workpiece surface.

countersinking

An operation that cuts a conical surface into a hole. Countersinking allows the head of a screw with a matching conical angle to rest flush with the workpiece surface.

crests

The external ridge, or high point, of a thread. Crests of screw threads fit in the internal grooves, or low points, of a tapped hole.

cutting fluid

A type of coolant used to cool or lubricate a metal cutting process. Cutting fluids are typically oil- or water-based liquids.

cutting speed

The rate at which a single cutting edge of a cutting tool rotates in one minute. Cutting speed is measured in surface feet per minute (sfm) or meters per minute (m/min).

deflecting

Unintentionally deviating from a straight line or plane when a force is applied. Deflecting in drilling can cause poor hole location and dimensions.

depth factor

A set of constant fractions used to determine the proper depth for common countersink angles. The depth factor for the angle multiplied by the fastener head diameter determines the depth.

dowel pin

A short, cylindrical rod. Dowel pins are fitted tightly into holes to prevent motion or slipping.

drill bushings

A hardened steel tube used to guide holemaking cutting tools such as drills and reamers. Drill bushings are used when a counterbore tool does not have a pilot.

drill chuck

A type of toolholder that tightens to grip holemaking tools on the mill. Drill chucks allow for quick installation and removal of various tools.

drill point

The tip of a drill that contains the cutting edges. The drill point performs all cutting as the drill moves into the workpiece.

drilling

The process of using a multi-point, or multi-edge, tool to penetrate the surface of a workpiece and make a round hole. Common drilling operations include center drilling and twist drilling.

edge finder

A rod shaped tool used to find the exact edge of a part along the X and/or Y axis. Edge finders are commonly used in milling to locate part zero.

end milling

A milling operation that uses a narrow mill to create slots, pockets, and contours in a workpiece. End milling may cut with both the bottom and sides of the cutting tool.

face milling

A milling operation that produces a flat workpiece surface using a face mill cutter. Face milling is primarily used on the top workpiece surface.

flush

Two or more level, adjacent surfaces. Flush surfaces form a flat plane.

flutes

A straight or helical recessed feature on the periphery of a cutter. Flutes allow chips to flow away from the cut.

knee crank

A handle used to raise and lower the knee and worktable on a milling machine. The knee crank features a micrometer dial that allows operators to adjust the feed rate incrementally.

length-to-diameter ratio

L/D ratio. A numerical value comparing the length of a cylindrical tool or workpiece to its diameter. Higher length-to-diameter ratios offer less rigidity; 4 to 1 is typically the maximum ratio for standard cutting tool steels.

machinability

The relative ease with which a machining process, such as milling or turning, can remove workpiece material. Machinability depends on the properties of the workpiece material.

major diameter

The distance from crest to crest of an external thread or from root to root of an internal thread. Major diameter is also called thread diameter.

micrometer adjustment nut

A nut located on a threaded rod that is used to determine spindle depth. Micrometer adjustment nuts are numbered in thousandths of an inch or hundredths of a millimeter.

mill

A manual machine that uses various cutting tools to remove metal from the surface of a workpiece. Mills are also called milling machines.

milling machine

A manual machine that uses various cutting tools to remove metal from the surface of a workpiece. Milling machines are also called mills.

minor diameter

The distance from root to root of an external thread or from crest to crest of an internal thread. Minor diameter of a tap measures the farthest distance from root to root on opposite sides of the tool.

multi-point

A cutting tool that has two or more cutting edges. In holemaking, multi-point tools may also be known as multi-edge tools.

pilot

The end of the counterboring tool that helps guide the cutter straight into the hole. Pilots are smaller than the rest of the tool and concentric to the drilled hole.

pin gage

A hardened, cylindrical gage used to inspect the size of a hole. Pin gages are available in standard diameters.

pitch

On a thread, the distance between a point on an individual thread to the corresponding point on the next thread. Pitches range from coarse, with few teeth, to fine, with many teeth.

pitch diameter

The measured distance between points in the grooves between threads. Pitch diameter is the theoretical point where the threads of a fastener and the threads of a hole meet.

reamer

A multi-point, or multi-edge, cutting tool with straight cutting edges, used to enlarge or smooth holes that have been previously drilled. Reamers may have straight or helical flutes.

reaming

The process of using a fluted, multi-point tool to produce to remove small amounts of material from the interior surface of a hole. Reaming achieves tight tolerances and refined surface finishes.

reference point

The established location of a tool, workpiece, or machine component. A reference point provides a location to accurately measure and create part features in a milling operation.

rigidity

The condition of a workpiece, machine, or machine setup characterized as still and immoveable. Rigid components are fixed securely in place.

roots

The internal ridge, or low point, of a thread. Roots of screw threads fit against the external crests, or high points, of a tapped hole.

scale dial

An analog device that measures linear movement. Scale dials are numbered collars attached to the feed handles and knee crank on manual mills.

shoulder

A flat step or plane in between two surfaces. Shoulders within holes provide space for nuts and screws to sit below the top surface of a workpiece.

spindle depth

The distance inside the workpiece that the spindle reaches during a cutting operation. Spindle depth on the manual mill is controlled by setting the micrometer adjustment nut or using the knee crank.

spindle speed

The rate at which the machine spindle rotates. Spindle speed is typically measured in revolutions per minute.

surface finish

The degree of smoothness of a part’s surface after it has been manufactured. Surface finish is the result of the surface roughness, waviness, and flaws remaining on the part.

tap

A cylindrically shaped, threaded device that either cuts or presses threads into the interior of a pre-drilled hole. A tap’s external teeth match the internal threads it is designed to produce.

tap drill size

The size of the drill required to create a specific threaded hole. Tap drill size determines the size of the hole before tapping.

tapping

The process of cutting internal threads in a round hole with a multi-point tool. Tapping is performed only after first drilling a hole.

tapping fluid

A substance used to cool and lubricate the cutting tool and workpiece in a tapping operation. Tapping fluid is typically oil-based.

telescope gage

A measuring instrument with a spring-loaded device used to check the inner diameter of a part. Telescope gages are then measured with a micrometer to get the proper value.

thread diameter

The distance from crest to crest of an external thread or from root to root of an internal thread. Thread diameter is also called major diameter.

thread gage

A measuring instrument used to inspect the threads of a part. Thread gages are made for either internal or external thread inspection.

threads

A long, spiraling groove that may appear on the interior or exterior of a workpiece surface. Threads help fasteners, such as screws, grip material and hold components together.

through hole

A hole that passes through the entire thickness of a workpiece. Through holes pass through two workpiece surfaces and have no bottom.

tolerances

A blueprint specification indicating an unwanted but acceptable deviation from a given dimension. Tolerances state the allowable difference between a part and its intended design.

twist drill

A common drill characterized by helical flutes along its length and two cutting edges at the drill point. Twist drills commonly have an 118° or 135° tip.

walking

Unintentionally moving off-center or away from the intended tool location. Walking is another term describing deflection.