NIMS Core Manual Milling Skills 261

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.

adjustable hand reamer

A type of hand reamer that expands and contracts slightly to sizes within a small range. Adjustable hand reamers are often used for oddly sized holes.

adjusting screw

A screw that gradually moves a machine component with each turn. The adjusting screw on the manual mill head allows the operator to align the head in the X axis.

alignment

The accurate positioning of machine components. Alignment of the mill head to the worktable is an important step of setup for the manual mill.

alignment pins

A cylindrical metal fastener that secures a workpiece or workholding device into position. Alignment pins inserted in a worktable's T-slots can securely hold a vise.

angle vise

A type of vise that can position the workpiece at an angle. Angle vises can be adjusted from zero to 90 degrees.

arbor

The bar attached to the spindle of a horizontal milling machine. The arbor holds the milling cutter for different types of milling processes.

axes

An imaginary straight line that is used to measure the location of an object in three-dimensional space. The Cartesian axes are the X, Y, and Z axes.

bar stock

Raw material purchased from metal manufacturers in the form of solid, long bars. Bar stock may be round, square, rectangular, or hexagonal.

base

The foundation of a machine that supports all the other machine components. The base of a milling machine is typically square or rectangular.

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.

bushing

A hardened steel tube that guides drills, reamers, and other cutting tools. Bushings ensure a cutting tool enters a drilled hole at the correct angle.

carbide inserts

A replaceable cutting edge made of hard carbide material that has multiple cutting edges. Milling cutters often use carbide inserts as cutting teeth.

carbon tool steel

A type of steel designed with improved wear resistance, toughness, and strength. Hand reamers are commonly made of carbon tool steel.

Cartesian coordinate system

A system that describes the location of an object by numerically expressing its distance from a fixed position along three linear axes. Cartesian coordinates are used to direct machine tool movements.

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.

centerline

An imaginary line that runs through the center of a cylindrical tool. The centerline of an edge finder pin is aligned to the part edge when the pin jumps off.

chamfer

An angled surface that eliminates a sharp corner, removes burrs, and/or aids in assembly. Chamfers generally replace a 90° angled surface with a 45° angled surface.

chip clearance

The space necessary for the proper formation and evacuation of small pieces of metal cut from a workpiece. Chip clearance prevents chip jamming and cutting tool failure.

chips

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

clamp bolts

A cylindrically shaped, threaded device for fastening parts. Clamp bolts hold the mill head and other components securely in a rigid position until the bolts are loosened.

climb milling

A type of milling that feeds the workpiece in the same direction as the cutting tool rotation. Climb milling creates chips that become gradually narrower during the cut.

coarse

A cutting tool pitch with less inserts, spaced farther apart. Coarse pitch face mills remove more material than finer pitch face mills.

collet

A split-sleeve device that expands or contracts to grip a cutting tool as it rotates. Collets come in various sizes to match specific tool diameters.

column

The vertical support, or backbone, of a milling machine. The column is supported by the machine base.

column and knee milling machine

A milling machine whose spindle is mounted in the column, and whose worktable rests on an adjustable knee. Column and knee milling machines are the most common type of manual mill.

concentric

Rotating in a perfectly circular motion. Concentric is the opposite of eccentric.

contours

A curved, non-linear dimension created by a cutting process. Contours can be created by precise tool movements in milling.

conventional milling

A type of milling that feeds the workpiece against the cutting tool rotation. Conventional milling creates chips that become gradually wider during the cut.

cross section

A surface or shape that is exposed or would be exposed by making a cut at a right angle to the object's axis. The cross section of a bar stock piece may be rectangular, square, hexagonal, or round.

cutting

The use of single- or multi-point tools to separate metal from a workpiece in the form of chips. Cutting processes vary based on the requirements of a finished part.

deflecting

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

diameters

The distance measuring from one side of an object to the other through its center. The diameter of a circle is always twice its radius.

dovetail cutters

A mill cutter used to cut a dovetail angle into a workpiece. Dovetail cutters can produce angled slots.

drill chuck

A type of toolholder that holds drill bits on the mill. Drill chucks allow for quick installation and removal of drill bits.

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

Using a multi-point tool to machine a new round hole into the surface of a workpiece. Drilling operations, which require a constant rpm, can be done on a drill press, lathe, or mill.

DRO

Digital readout. A type of readout that uses an encoder attached to a machine that transfers information to a digital display. DRO is capable of very precise measurements.

eccentric

Rotating in an erratic, non-circular motion. Eccentric is the opposite of concentric.

edge finder

A rod-shaped tool that operators use to find the exact edge of a part. Edge finders are commonly used in milling to locate part zero.

end mill

A type of milling cutter that performs both peripheral and face milling with its bottom and side cutting edges. End mills can be used to machine grooves, slots, circular slots, pockets, and contours.

end mill toolholder

A toolholder that holds an end mill in place with a set screw. End mill toolholders hold tools with more rigidity than collet-type toolholders.

end milling

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

expansion reamer

A type of hand reamer that expands slightly with a screw. Expansion reamers only expand and do not contract; the diameter expansion is permanent.

face

The bottom surface of a mill or mill tooth. The face is the primary cutting surface used in face milling.

face mill

A wide, round milling cutter that contains multiple cutting teeth and is often used to remove large amounts of material. Face mills cut with their face and periphery.

face milling

A milling operation that produces a flat workpiece surface using a face mill cutter. Face milling is primarily used to remove large amounts of material from the workpiece's top surface.

feed handles

A handle attached to a machine that controls the movement of a component. Feed handles, or handwheels, on the milling machine move the table side to side and forward and backward.

feeds

The rate at which the cutting tool and the workpiece move in relation to one another. Feed is typically a linear movement.

fine

A cutting tool pitch with more inserts, spaced close together. Fine pitch face mills remove less material but produce a smoother surface finish than coarse pitch face mills.

finishing

The final cuts taken with the cutting tool to obtain the accuracy and surface finish desired. Finishing operations often require faster cutting speeds.

fixture plate

A large flat piece of stock clamped to the worktable. Fixture plates provide a flat surface for workholding without interference from the worktable's T-slots.

flutes

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

full-side cutters

A narrow, wheel-shaped milling cutter with teeth on both sides of its periphery. Full-side milling cutters are used on horizontal mills to create vertical workpiece features.

gear

A round or cylindrical mechanical component with teeth that transmits power. Gears mesh with one another and can alter the speed, torque, or direction of mechanical energy.

gib

A device used to reduce side play in the mill table as it is moved from one direction to another. Gibs are placed between the ways and the table.

half-side cutters

A narrow, wheel-shaped milling cutter that has teeth on one side of its periphery. Half-side milling cutters are used on horizontal mills to create vertical workpiece features.

hand reamer

A manual cutting tool that smooths or enlarges existing holes. Hand reamers have a straight shank and a square tang, or peg, that can be gripped with a tap wrench.

hand reaming

A type of benchwork operation that involves manually removing small amounts of workpiece material to enlarge an existing hole. Hand reaming is performed on holes that require tight tolerances.

head

The part of the vertical milling machine that holds the spindle. The head also contains various speed and feed controls for the mill.

heat treatment

Controlled heating and cooling processes used to change the structure of a material and alter its physical and mechanical properties. Heat treating is often used to adjust a material's hardness.

helical

Winding around in the shape of a spiral, spring, or coil. End mill and drill flutes are helical.

helical-fluted hand reamer

A type of hand reamer with spiral-shaped flutes. Helical-fluted hand reamers are often used to ream holes with keyways or interruptions.

hexagonal

Six-sided. Hexagonal is a standard bar stock shape.

horizontal column and knee milling machine

A milling machine with a spindle that is parallel to the ground and machine worktable. Horizontal column and knee milling machines are less common than vertical column and knee milling machines.

indexable

Having multiple cutting edges that can be repositioned to reveal a fresh cutting edge. Indexable inserts on a face mill can be rotated to a different cutting edge once the original edge has been worn or damaged.

indicator pin

A point on the end of the dial indicator. Indicator pins run across two or more surfaces to measure differences in distance.

jaw

A component on a vise that grips and holds the workpiece in place. Jaws of a vise used in a milling operation are adjustable.

jump off

An abrupt, but slight, off-center shift of the edge finder pin. Jump off indicates that an edge finder has located a workpiece edge.

keyways

A rectangular slot or groove that is machined down the length of a hole. Keyways make up the specific design of a keyhole.

knee

The device that supports the mill worktable from underneath. The knee can be used to adjust the worktable to different heights.

knee crank

A handle that raises and lowers the knee and worktable of a manual milling machine. Knee cranks allow 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.

linear

In a straight line along a single axis. Linear workpieces can be aligned on a mill worktable using a precision machinist square.

locate

To establish a designated location. Locating part zero sets a starting point on the workpiece for a manual milling operation.

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.

manual mills

A machine controlled by an operator that uses a multi-point tool to remove metal from the surface of a workpiece. Manual mills are classified by the spindle orientation as vertical or horizontal.

manufacturer’s technical data references

Documents provided by a manufacturer that provide specific information about the products they manufacture. Machinists use manufacturer’s technical data references to help them select the proper cutting tool for a given operation.

milling

A cutting operation in which a rotating multi-point cutting tool is fed along a part's surface to remove material. Milling operations are very versatile and generally produce flat surfaces.

milling machine

A machine that uses a multi-point tool to remove metal from the surface of a workpiece. Milling machines are also called mills.

multi-point tool

A cutting tool that has more than one cutting edge. Multi-point tools include mills and drills.

origin

The fixed central point in the Cartesian coordinate system. The origin has a numerical value of zero at each axis.

overarm

The part of the horizontal milling machine that reaches over the workpiece and worktable. The overarm supports the spindle and arbor.

parallel

Two lines or axes that are equidistant from each other at all points along their length and thus never intersect. On a horizontal mill, the spindle is parallel to the worktable.

parallels

Two rectangular strips or blocks of precision metal that help support the workpiece in the vise. Parallels allow for raising the workpiece to the desired working height in the vise.

part zero

The starting point of X, Y, and Z coordinates for a specific workpiece. Part zero acts as a reference point for all part dimensions.

periphery

The outer edge or rim of an object or tool. Both the periphery and face of the cutting tool are used in face milling.

perpendicular

Meeting at a right angle. On a vertical mill, the spindle is perpendicular to the worktable.

pitches

The relative quantity of teeth on the periphery of the milling cutter. Pitch ranges from coarse, with few teeth, to fine, with many teeth.

plunge milling

A milling operation that uses the face of an end mill, face mill, or specialized milling cutter to cut straight down into a workpiece from above. Plunge milling creates scalloped edges that require a finishing pass to remove.

pockets

An enclosed recess machined into a workpiece surface. Most pockets are square or rectangular with rounded corners.

precision machinist square

An L-shaped tool that a machine operator can use to align square or linear workpieces. Precision machinist squares are less exact than indicators.

precision-ground parallels

A pair of metal support blocks that machinists use to position a workpiece to the desired working height in a vise. Parallels are made using highly accurate precision grinding processes to ensure both blocks have equal thickness.

quick-change tooling

A toolholding system that uses a master toolholder with a set of interchangeable toolholders. Quick-change tooling increases the speed of production.

radius

The distance between a point on a circle's circumference and its center. The radius of an edge finder's pin must be factored into locating an exact workpiece edge.

reaming

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

reference point

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

retrofit

To modify a machine or tool with a new part. Retrofitting manual mills with quick-change tooling reduces the time spent changing toolholders.

rigidity

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

rotary bases

A rotating base on the bottom of the vise. Rotary bases can position the workpiece at a variety of angles to the X and Y axes.

roughing

The initial machining operation that removes stock rapidly without regard to surface finish. Roughing achieves the basic workpiece shape and dimensions in milling.

roughing cuts

An initial pass of the cutting tool that emphasizes heavy metal removal rates, high feed rates, and a heavy depth of cut. Roughing cuts are made prior to finishing operations.

saddle

A machine component that moves the worktable back and forth from the column. The saddle on a column and knee machine rests on the knee.

set screw

A type of screw, often with no head, used to hold a device in place relative to other components. Set screws are used with end mill toolholders.

shank

A long cylindrical part of a tool or device, such as a drill or a reamer. The shank of a reamer has flutes.

shim stock

A thin sheet or roll of sheet metal that is machined into custom shims. Shim stock is sometimes used to adjust the gibs on manual mill ways.

slot

A narrow channel cut into the surface of a workpiece. Slots can be created with either a face or end mill.

slotting

A milling operation that cuts a long, rectangular channel into the surface of a workpiece. Slotting uses a circular disk-like cutter.

speed range

A limited set of possible speeds at which a machine is capable of running. Speed ranges for a manual mill include high and low range.

speeds

The rate at which the workpiece passes the cutting tool at the point of contact. Surface speed has the greatest effect on tool life.

squaring

The process of making the sides of a part even and parallel using a face milling operation.

step

A raised or lowered flat surface in a series of workpiece surfaces. Steps on a workpiece can be created by face milling and end milling.

step-over

The amount of a face mill cutter's diameter that is engaged in a cut. Step-over should be no more than 75% of the cutter's diameter.

straight-fluted hand reamer

A type of hand reamer with straight flutes. Straight-fluted hand reamers are the most common types of hand reamers.

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.

symmetrical

A part that can be divided by a line into two equal halves, with identical features that are equal distances from the dividing line. On a symmetrical part, both sides appear as mirror images of each other.

tang

A square extension on the end of a reamer. Tangs allow reamers to be secured in tap wrenches.

teeth

Cutting edges on the perimeter of a circular tool. Teeth perform the cutting action while flutes clear chips.

tool center

A line or point of a cylindrical tool that is equally distant from all other points located on the tool's circumference. Tool centers are located by subtracting the tool's radius from any point on its circumference.

tool life

The length of time a cutting tool is expected to be operational before it must be replaced. Tool life can be extended through optimized implementation, including the proper tool geometry or using cutting fluids.

toolholders

The device used to rigidly hold a cutting tool in place. Toolholders may hold inserts or larger tools.

torque

The ability of a machine to exert a rotating force at a particular speed. The torque of a machine varies across its speed range.

tram

Aligning the mill head so that it is at 90° to the worktable. A mill must be trammed parallel to the X axis and the Y axis.

T-slot cutters

A T-shaped milling cutter that machines a portion of a T-shaped slot into a workpiece. T-slot cutters often resemble a toothed disk mounted on a narrow arm.

T-slots

A T-shaped opening running the length of a machine worktable. T-slots allow operators to use workholding devices during machining processes.

T-slotting

A milling operation that uses a T-shaped milling cutter to cut a channel shaped like an inverted T into a workpiece. T-slotting is often used to machine worktables.

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.

vertical column and knee milling machine

A manual milling machine with a spindle that is perpendicular to the ground and machine worktable. Vertical column and knee milling machines are more common than horizontal mills.

vise

A workholding device with two jaws that grip and hold a workpiece in place. Vises are often used to hold workpieces on the mill.

V-ram

The moveable component attached to the mill head. The V-ram facilitates the machining of oversized parts or long parts that hang over the edge of the mill table.

ways

Two parallel rails that guide the movement of a machine component. Ways keep the mill worktable straight and parallel to the knee as it moves.

worktable

A machine component that supports the workpiece and any workholding devices. The worktable on a manual mill moves side to side and back and forth.

X axis

The Cartesian axis representing coordinate positions along the longest distance parallel to the worktable. The X axis describes a mill worktable's side-to-side movement.

Y axis

The Cartesian axis representing coordinate positions along the shortest distance parallel to the worktable. The Y axis describes a mill worktable's forward-and-backward movement.

Z axis

The Cartesian axis representing coordinate positions along a line parallel to the tool spindle and perpendicular to the worktable. The Z axis describes vertical, up-and-down movement.