Manual Mill Operation 251

analog measurement

A type of readout that uses dials with scales inscribed on them to display dimensions on the mill. Analog measurement is less precise than digital readout.

approach distance

A small distance that the cutting tool travels before engaging the workpiece. The approach distance is added for safety reasons.

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. Axes in the Cartesian coordinate system include the X, Y, and Z axes.

backlash

The relative movement of interlocked mechanical components due to slack, or extra space, between them. Backlash often occurs when motion is reversed.

ballscrew

The threaded device that controls the precise movement of the various components of the mill. On the mill, ballscrews are connected to the feed handles and knee crank, which an operator rotates to move the worktable.

base

The foundation of a machine that supports all other machine components. Bases stabilize mills and provide them with rigidity.

blueprint

A document containing all the instructions necessary to manufacture a part. A blueprint, or print, includes a part drawing, dimensions, and notes.

burrs

A rough, sharp edge remaining on a part after a cutting process. Burrs pose an injury risk and interfere with the fitting of parts.

caliper

A measuring instrument with two pairs of jaws on one end and a long beam containing a marked scale of unit divisions. One pair of jaws measures external features; the other pair measures internal features.

calipers

A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions. Calipers can measure both internal and external features.

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.

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 before drilling to ensure that the hole is machined on centerline.

chamfer

To eliminate a sharp 90° corner on a workpiece by cutting a 45° angle into the edge. On the manual mill, chamfering can be done with a hand tool, or a tool in the machine spindle.

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.

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 a finer pitch face mills.

column

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

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.

cutting tool

A device with one or more edges used to create chips and remove material. Cutting tools are either single-point or multi-point tools.

cutting variables

The changeable aspects of a given metal cutting operation. Cutting variables for milling operations include speed, feed, and depth of cut.

dead blow hammer

A type of hammer that gives a solid blow to different materials without damaging their surfaces. Dead blow hammers can be made of plastic, rubber, brass, or lead.

deflection

The unintended repositioning or bending movement of a drill due to mechanical force. Deflection of a drill can cause poor hole location and inaccurate hole dimensions.

depth of cut

The thickness of material removed by one pass of the cutting tool. Depth of cut measures how far the cutting tool penetrates the surface of the workpiece during a cut.

diameter

The distance from edge to edge of the widest point of a circle. The diameter of a circle is always twice its radius.

digital readout

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

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 press

A machine tool that can be used for a variety of hole-making operations. Drill presses create round holes in workpieces.

drilling

The process of using a multi-point tool to penetrate the surface of a workpiece and make a round hole. Drilling is a common holemaking operation.

edge finder

A rod shaped tool used to find the exact edge of a part. Edge finders are commonly used in milling to find the exact location of a hole.

encoders

A device that translates mechanical motion into a digital signal. Encoders send locations to display panels on manual mills with digital readout.

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.

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.

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

The rate at which the cutting tool and the workpiece move in relation to one another. Feeds in manual milling are measured in inches or millimeters per minute or per revolution of the cutting tool.

feed

The rate at which the cutting tool and the workpiece move in relation to one another. On the mill, feed often describes a linear movement of the cutting tool into the workpiece to remove material.

feed handles

A handle attached to a machine that controls the movement of a component. Feed handles on the milling machine move the table side to side and back and forth.

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

A final metal cutting pass that emphasizes tight tolerances and smooth surface finish. Finishing cuts often require faster speeds and a lighter depth of cut.

finishing

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

finishing material

The small amount of material that is intentionally left for a finishing pass. Finishing material is used to ensure good workpiece finish and tolerance.

flutes

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

glass scale encoders

An encoder that uses light sensors to detect movement. Glass scale encoders are the most accurate encoders because they are not subject to backlash.

head

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

helical

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

horizontal column and knee mill

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

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.

knee

A manual mill component that supports the saddle. Knees can also be used to adjust a mill’s worktable to different heights.

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.

layout

The marking of lines, centers, or circles on metal workpieces. Layout shows the size, shape, and locations of features.

layout dye

A fluid that is brushed on a metal workpiece before layout. Layout dye allows the lines and features to be seen more clearly.

manual milling

A milling operation where machine movements are controlled by an operator. Manual milling is most commonly performed on the vertical column and knee mill.

metal cutting

A machining process that uses a tool to remove metal from a workpiece in the form of chips. Metal cutting operations include milling, drilling, and turning.

micrometer

A handheld measuring device used to inspect the dimensions of parts. The typical micrometer is accurate within 0.001 in. or 0.020 mm.

micrometer adjustment nut

A nut located on a threaded rod that is used to determine spindle depth. The micrometer adjustment nut on a mill head is numbered in thousandths of an inch or hundredths of a millimeter.

milling

The use of a rotating multi-point cutting tool to machine flat surfaces, slots, or internal recesses into a workpiece. Milling includes a wide range of versatile metal cutting operations.

milling machine

A machine that uses a rotating, multi-point tool to remove material from a workpiece. Milling machines, or mills, may be manually operated or automated.

mills

A machine that uses a rotating, multi-point tool to remove material from a workpiece. Mills may also refer to cutting tools used on the mill.

multi-point tool

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

numerical display panel

The screen that displays information about a machine for the operator. Numerical display panels indicate the position of the workpiece on a manual milling machine.

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

A pair of vertical metal supports that are used to position the workpiece to the desired working height in the vise. Parallels are positioned directly within the vise jaws.

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 90° angle. On a vertical mill, the spindle is perpendicular to the worktable.

personal protective equipment

PPE. Any of the various articles of clothing or safeguarding devices that assemblers or operators are required to wear to ensure their safety. Personal protective equipment for a milling operation includes safety glasses.

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.

pockets

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

print

A document containing all the instructions necessary to manufacture a part. A print, or blueprint, includes a part drawing, dimensions, and notes.

quill

A shaft that moves the spindle in and out of the mill head. The quill feed handle controls the quill's main vertical movements.

readout

The process of reading information from a machine and displaying it in an understandable form. Readout measures locations and movements on a mill and can be analog or digital.

reference point

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

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.

referencing

Locating a tool, workpiece, or machine component in a known position. Referencing is used to measure and create part features in manual milling operation.

rigidity

The property of a workpiece, machine, or machine setup characterized as stiff and immoveable. A mill’s rigidity is provided by its base.

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.

rules

A simple measuring instrument consisting of a long, thin metal strip with a marked scale of unit divisions. Rules come in many sizes and forms and can be rigid or flexible.

saddle

A mill component that enables the worktable to move side to side and back and forth. Saddles are located between the knee and worktable on a mill.

scale dials

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

scribing

Drawing fine lines or features on a workpiece surface during layout. Scribing is done with a fine pen-like, hard-pointed tool.

setting zero

Creating a known location on a machine. Setting zero establishes a reference point by setting the readout to 0 in each axis.

setup

All the necessary preparation of tooling and fixturing that occurs on a machine before an operation can be executed. Setup includes preparing machines, tools, and materials.

shim

A thin or tapered material used to support a workpiece. Shims may also be used to prevent damage to a workpiece surface when touching off with the cutting tool.

slots

A narrow channel cut into the surface of a workpiece. Slots can be machined by end milling or face milling operations, depending on the width.

specifications

The design parameters that set the limits of acceptable deviation for a part’s intended application. Specifications are also called specs.

spindle

The part of a machine tool that spins or rotates. On the mill, the spindle holds the cutting tool.

spindle depth

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

squares

A precision measuring instrument with two straight edges that meet at a right angle. Squares are commonly used in milling layout and setup.

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.

stock

Raw material that is used to make manufactured parts. Stock is available in standard shapes such as long bars, plates, or sheet.

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. Both sides appear as mirror images of each other.

tapping

The process of cutting internal threads in a round hole with a multi-point tool. Tapping can be performed on a manual mill or a drill press.

teeth

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

three-dimensional

A space that has length, width, and depth. Three-dimensional space can be represented by the Cartesian coordinate system.

through holes

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

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.

toolholder

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

tooling

Assorted cutting tools used in various manufacturing processes. Tooling used in milling includes face mills, end mills, and holemaking tools.

touch off

To determine the exact location of a tool tip by touching it against an object with a known measurement. Touching off is the first step in a squaring operation and locates the cutting tool in the Z axis.

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 118-135° angle tip.

vertical column and knee mill

A manual mill with a spindle that is perpendicular to the floor and machine worktable. Vertical column and knee mills, or 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.

walking

The tendency of a drill to move off-center of the intended hole at the beginning of a drilling operation. Walking is prevented by center drilling prior to the drilling operation.

workholding

A device used to hold and locate a workpiece. Workholding is used to keep the workpiece stationary on a mill.

worktable

The machine component that supports the workpiece and any workholding devices during machining. Worktables on manual mills move side to side, back and forth, and up and down.

X axis

The Cartesian axis describing left to right movement. On the mill, the X axis represents coordinate positions along the longest distance parallel to the worktable.

Y axis

The Cartesian axis describing in and out movement. On the mill, the Y axis represents coordinate positions along the shortest distance parallel to the worktable.

Z axis

The Cartesian axis describing vertical movement. The Z axis is always parallel to the machine tool spindle on a vertical mill.