Manual Mill Operation 251

acetone

A solvent that can be used to clean certain types of contaminants from a surface. Acetone can be used to clean a workpiece before and after applying layout dye.

aluminum

A lightweight metal that is silvery-white in color. Aluminum is highly machinable.

asymmetrical

Having features on either side of a point, line, or plane that differ in size, shape, or position. Asymmetrical parts have clearly distinguished sides.

axial depth of cut

The amount of peripheral cutting edges that are engaged with the workpiece in a single pass. Axial depth of cut, sometimes called AP, measures how far beneath the workpiece surface the peripheral cutting edges penetrate.

axis keys

The individual keys representing Cartesian Coordinates on a digital readout system. Axis keys can be used to set the axis in a particular position or to zero out the axis.

ball end mill

An end mill with a fully rounded end. Ball end mills cut rounded edges and complex three-dimensional shapes into workpieces.

bevels

A sloping surface or edge. Bevels may be created in a workpiece using a chamfer end mill.

block squaring

The face milling of a rectangular part on all six sides. Block squaring ensures that the part is positioned accurately in the vise.

blueprint

A design representing the dimensions of a specific finished part. Blueprints include part drawings, dimensions, and notes.

boring

A cutting operation in which an existing hole is enlarged. Boring can be done on either a lathe or a mill.

boring tool

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

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.

center drilling

A drilling process in which a preliminary hole is made in a workpiece in order to guide the drill used to finish the hole. Center drilling can help prevent a drill from walking.

chamfer end mill

An end mill with an angled face between the axial and radial cutting edges. Chamfer end mills cut angled edges into workpieces.

chamfers

A small, angled surface added to the edge of a workpiece. A chamfer removes the sharp edge and helps eliminate burrs.

chatter

Occasional unwanted vibration between components. Chatter decreases productivity and can cause wear.

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.

chip evacuation

The proper clearance of chips during a metal-cutting process. Chip evacuation can become an issue if the operation generates a lot of vibration, as with grooving, or does not utilize enough cutting fluid, which can result in a damaged cutting tool or scrapped part.

chip load

The linear distance traveled by the cutter during the engagement of a single cutting tooth. Chip load, which is also known as feed per tooth (fpt), is the feed measurement for multiple cutting edge tools.

chips

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

circumference

The boundary or outside edge of a circle. Circumference measures the distance around a circle.

coarse

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

compressed air

Air that has been forced into a small space at a high pressure. Compressed air can be used to clean out chips during milling.

coolant

A cutting fluid used for lubrication and for decreasing the temperature of the tool and workpiece to prolong tool life. Coolant must be manually added when operating a manual mill.

corner radius end mill

An end mill with a rounded face between the axial and radial cutting edges. Corner radius end mills cut features with rounded edges into workpieces.

counterboring

A holemaking operation that enlarges one end of a previously drilled hole to a certain depth. Counterboring allows room for the head of a fastener such as a nut or bolt.

countersinking

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

cutting edge length

The portion of the cutting tool that removes material. Cutting edge length should be considered based on the required depth of cut for each operation.

cutting fluid

A liquid used to cool or lubricate a metal cutting process. Cutting fluids are typically oil-based, water-based, synthetic, or a blend of liquids.

cutting speed

In milling, the rate at which the cutting edge of a cutting tool rotates. Cutting speed is measured in surface feet per minute (sfm) or meters per minute (m/min).

cutting zone

The area of contact between the cutting tool and the workpiece. The cutting zone is often lubricated and cooled through the use of metal cutting fluids.

deburr

The removal of sharp projections left by a tool on a workpiece. Deburr the workpiece to ensure it has smooth, flat edges.

deflection

The unintended movement or deviation of a tool due to the application of mechanical force. Deflection of a tool can cause inaccurate dimensions.

depth of cut

DOC. 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

A line measuring the distance from one edge of a circle to the opposite edge that passes through the center. 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 provides precise measurements.

DOC

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

drilling

A holemaking process in which a rotating cutter makes a round hole in the workpiece to a certain depth. Drilling can be performed on a manual mill.

drills

A cutting tool used to create holes in workpieces. Drills are common tools for holemaking operations.

DRO

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

edge finder

A rod shaped tool with an eccentric rotation used to find the exact edge of a part. Edge finders kick when they contact the workpiece and locate the exact edge.

encoders

A device that translates mechanical motion into a digital signal. Encoders send the location of a workpiece to the display panel using digital readout on a manual mill.

end milling

A milling operation that uses a narrow cutter to machine surfaces both parallel and perpendicular to the spindle axis. End milling cutters 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 flat mill cutter with multiple cutting teeth surrounding the bottom edge. Face mills cut with their face and periphery.

face milling

A milling operation in which the surface of a workpiece is perpendicular to the spindle axis. Face milling is primarily used for creating recessed indentations with flat bottoms, such as pockets, slots, and grooves.

facing

A cutting operation where a tool is fed across the end of a cylindrical workpiece to create a flat surface and shorten its length. Facing is performed on a lathe or mill.

feed per tooth

fpt. The linear distance traveled by the cutter during the engagement of a single cutting tooth. Feed per tooth, which is also known as chip load, is the feed measurement for multiple cutting edge tools.

feed rate

The rate at which a cutting tool moves in relation to workpiece during a milling operation. Feed rate can be adjusted during operation using override keys.

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

fixed jaw

An unmoving component on a vise that grips and holds the workpiece in place. A vise has one fixed jaw and one moveable jaw.

fixture

A custom workholding device that is designed to effectively support, locate, and hold a specific type of workpiece. A workpiece with multiple, complex dimensions often requires a dedicated fixture.

flutes

A groove on the periphery of a cutter that provides room for chips to flow away from the cut. Flutes are present on some mill cutting tools.

height gage

A measuring device with a column mounted on a base such as a granite surface plate, a unit that slides up and down, an indicator, and an arm that extends out. Height gages are used to measure vertical and other distances and can scribe lines onto a part covered in layout dye.

helical

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

helix angle

The angle created by the center axis of the tool and the slope of the peripheral cutting edge. The helix angle, also known as the helical rake angle, can affect the strength of the cutting edge on a mill, among other properties.

high-speed steel

HSS. A common cutting tool material that is relatively inexpensive and that offers excellent toughness. High-speed steel tools are often heat-treated and coated.

holemaking

A machining operation in which a single- or multi-point cutting tool creates, sizes, or finishes a hole. Holemaking includes drilling, boring, reaming, and tapping.

inches

in. A small unit of linear measurement in the U.S. customary system. One inch equals approximately 2.54 centimeters metric.

indexable

A cutting tool with multiple cutting edges that can be rotated into place. Indexable inserts can be turned to expose a new cutting edge when one cutting edge wears out.

interior radii

The distance inside of a rounded or curved surface in the corners of a part. Interior radii should measure the same distance as the cutting tool when creating pockets.

layout

A manufacturing process during which a workpiece is marked with lines, centers, or circles to show how it should be machined. Layout occurs prior to the actual machining process.

layout dye

A colored fluid that a machinist brushes or sprays on a metal workpiece at the beginning of layout. Layout dye allows the lines and features to be seen more clearly.

length-to-diameter ratio

L/D ratio. A numerical value comparing the length of a cylindrical tool or workpiece with its diameter. Higher length-to-diameter ratios offer less rigidity.

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.

machinists

A person responsible for ensuring a machine performs its job correctly, efficiently, and safely. Machinists, or operators, are responsible for interpreting manufacturing prints and implementing the design using various metal cutting machines.

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.

millimeters

mm. A small unit of linear measurement in the metric system. One millimeter is equal to 0.1 of a centimeter metric and 0.039 of an inch U.S. customary.

milling machine

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

multi-point cutting tool

A machining tool that has two or more cutting edges. Multi-point cutting tools are often used on manual mills.

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.

order of operations

The process in machining of examining a blueprint to determine the sequence that a machinist will cut various part features. The order of operations does not have any strict rules but are generally arranged from simple to complex features.

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.

peck drilling

A drilling operation that periodically retracts the tool to clear chips or flood the hole with coolant. Peck drilling is often used for holes that are deeper than the drill diameter.

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.

personal protective equipment

PPE. An article of clothing or device worn to minimize exposure to hazards and prevent injury. Personal protective equipment for a milling operation includes safety glasses and steel-toed boots.

pitches

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

pockets

An enclosed recess machined into a workpiece surface. Pockets can be circular, rectangular, or irregular.

pounds per square inch

Psi. A measurement of pressure. Pounds per square inch is used to measure the pressure in a compressed air system.

radial depth of cut

The distance the cutting tool's cutting edges removes materials from the workpiece perpendicular to the tool's axis. Radial depth of cut uses a larger amount of the cutting edges on a cutting tool.

reamer

A multi-point cutting tool with straight cutting edges that is used to enlarge or smooth holes that have been previously drilled. Reamers look similar to a drill but lack a cutting point.

reaming

A machining operation that uses a multi-point tool to enlarge or smooth an existing hole. Reaming is performed to improve the surface finish and concentricity of a hole.

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.

revolutions per minute

Rpm. A measurement of speed that indicates how many times the spindle has rotated in one minute. Revolutions per minute is measured from the center of tool or spindle rotation.

roughing cuts

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

rpm

Revolutions per minute. A measurement of speed that indicates how many times the spindle has rotated in one minute. Rpm is measured from the center of tool or spindle rotation.

rulers

A simple measuring instrument consisting of a long, thin metal strip with a marked scale of unit divisions. Rulers 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.

scrap

A piece of unusable material produced during a manufacturing process. Scrap costs manufacturers time and money.

scribe

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

scriber

A pen-like layout tool. Scribers create fine lines on the surface of a workpiece.

side milling

A machining process where a rotating mill cutter removes materials from the sides of a workpiece. Side milling is generally preformed prior to drilling or boring.

slots

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

slotting

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

smearing

A condition that causes a tool to leave burrs on a workpiece when it is not properly lubricated during machining. Smearing causes a poor surface finish.

specifications

A description of the essential physical and technical properties of a finished part. Specifications include finished part dimensions and acceptable tolerance ranges.

spindle

A component of a machine that rotates or spins. The spindle holds and rotates the cutting tool on a manual mill.

spindle speed

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

square

A 90° orientation to another object. A cutting tool that is square to a workpiece is perpendicular to the workpiece axis or surface.

square end mill

An end mill with a 90° angle between the axial and radial cutting edges. Square end mills cut features with right angles into workpieces.

squares

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

steel

A ferrous metal consisting of iron and carbon, usually with small amounts of manganese, phosphors, sulphur, and silicon. Steels are less machinable.

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

step-over distance

The space between adjacent cuts made by a tool in a milling operation. Step-over distance is calculated by multiplying the diameter of the end or face mill by the chosen step-over percentage.

steps

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.

stock

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

symmetrical

Having completely identical features on either side of a point, line, or plane. Both sides of a symmetrical object have the same dimensions.

taper

A gradual decrease from a larger size to a smaller size at a constant slope or incline. A taper on a cylindrical part affects its entire diameter.

tapping

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

tapping

A metal cutting process that uses a rotating multi-point tool to produce internal threads in a workpiece. Tapping is performed only after first drilling a hole.

taps

A cylindrical cutting tool used to produce internal threads in a preexisting hole. Taps have thread forms on their outer surface that match the internal threads it is designed to produce.

teeth

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

threads

A long spiraling groove machined in the interior or exterior of a part. Threads allow compatible fasteners to connect to and move about each other.

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 using the proper tool geometry or cutting fluids.

tool wear

The erosion of tool material as a result of friction. Tool wear degrades the accuracy and precision of a tool.

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.

T-slotting

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

vertical column and knee mill

A manual mill with a spindle that is perpendicular to the ground 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. A vise is commonly used for workholding on the mill.

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 for locating and supporting a workpiece for cutting operations. Workholding is used to keep the workpiece stationary on a mill.

Z axis

An axis in the Cartesian coordinate system that represents motions and positions perpendicular to the X and Y axes. Z axis movement on the mill describes vertical, up-and-down movement.

zero out

Changing the digital reading to measure zero. Zeroing out a dial indicator or digital readout panel is essential for accurate measurements.