An array of milling tools is available, including endmills, facemills and plain mills. Typical milling applications include facing, filleting or edge cutting, profiling, slotting, pocketing and blind slotting.
There are several common endmill designs. Two-flute endmills with square ends are applied because they can make plunge cuts into the work like a drill and cut sideways. Their end teeth extend to their centers to allow plunge cuts. Some 3-flute endmills can also perform plunge cuts. Both 2- and 3-flute endmills are suitable for milling nonferrous metals. Two-flute endmills with a ball end produce rounded-bottom slots or filleted edges.
Four-flute finishing endmills with a square end make smoother cuts than 2-flute endmills and stay sharp longer, but cannot make plunge cuts. These tools are best suited for cutting ferrous metals. Four-flute roughing endmills remove metal faster with less horsepower, cutter deflection and vibration than 4-flute finishing endmills, and their chipbreakers produce smaller, more controllable chips.
Courtesy of All images: Pamela J. Tallman
Common endmill designs include (from top to bottom): 2-flute endmill, 2-flute ballnose endmill, 4-flute finishing mill and 4-flute roughing mill.
The helical shape of an endmill’s flutes reduces chatter. In operation, one or more points of the helical flutes remain in contact with the workpiece and cut metal at all times. This presents a continuous load to the machine instead of a pulsing load, which occurs each time a tool with a straight flute begins and ends contact with the work. Although making helical flutes is more complex and costly than straight ones, the reduction in chatter and the finer finish they produce is worth the extra cost.
Various common options are available for solid endmills. They are available for right-hand or left-hand cutting. Left-handed cutters are used when the direction of cutting forces must be reversed to avoid stressing the workpiece. In addition, endmills are offered with varying flute lengths, including stub, regular, long and extra long. Endmills can also have tapers. They are commonly tapered at ½°, 1°, 1½°, 2°, 3°, 5°, 7°, 10°, 15°, 20° and 25° per side. These are especially useful in moldmaking to provide draft, or taper, to ease the release of the molded product.
A plain milling cutter is able to rapidly remove a large volume of metal.
A facemill tooled with inserts.
Shell endmills cut on both their face and sides to impart a fine surface finish. Common diameters are from 1¼ " to 6 ", with flutes cutting from ½ " to ¾ " deep. Because of horsepower and rigidity limitations, vertical knee mills are limited to smaller shell mill sizes. Larger diameter ones can be applied to effectively mill aluminum and plastics.
Facemills are applied to smooth large, flat surfaces and to rapidly remove large volumes of metal. Facemills that accept inserts are available in a range of diameters, typically from ½ " to 3 ". When run on vertical knee mills, lack of mill frame rigidity and the resulting chatter limit those machines to smaller diameter facemills. Facemills are more suitable for massive C-frame mills. When facemilling softer materials, such as aluminum and plastics, larger diameter facemills can be used without chatter.
Plain milling cutters are usually applied on horizontal machining centers on an arbor supported at both ends. Horizontal endmilling machines provide the power and rigidity needed to fully utilize the high metal-removal rates possible with plain milling cutters. However, a horizontal milling attachment permits the use of plain milling cutters on vertical knee mills. This is a useful accessory, even though a vertical knee mill must take lighter cuts than a horizontal mill because of rigidity and chatter issues. In a vertical knee mill with a horizontal milling attachment, the plain milling cutter removes more metal faster than other cutters. In some instances when lacking a horizontal milling machine, using several cutters on the same arbor is simply the best way to do the job. Plain mills are usually wider than the workpiece and cut completely across it.
Plain side milling cutters are similar to plain milling cutters, but they can also cut on their sides. Plain side milling cutters also cut slots, cut off heavy metal bars, smooth faces and cut material into strips. They can be mounted on an R8 toolholder with a single-end support but are best employed in a horizontal milling machine or in a horizontal milling attachment on a vertical knee mill, which is more rigid. Like the plain milling cutter, plain side mills can be mounted with other milling cutters to take multiple cuts simultaneously. CTE
About the Author: Frank Marlow, P.E., has a background in electronic circuit design, industrial power supplies and electrical safety and has worked for Avco Missile Systems, Boeing, Raytheon, DuPont and Emerson Electric. He can be e-mailed at orders@MetalArtsPress.com. Marlow’s column is adapted from information in his book, “Machine Shop Essentials: Questions and Answers,” published by the Metal Arts Press, Huntington Beach, Calif.
Related Glossary Terms
- arbor
arbor
Shaft used for rotary support in machining applications. In grinding, the spindle for mounting the wheel; in milling and other cutting operations, the shaft for mounting the cutter.
- centers
centers
Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.
- chatter
chatter
Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.
- endmill
endmill
Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.
- endmilling
endmilling
Operation in which the cutter is mounted on the machine’s spindle rather than on an arbor. Commonly associated with facing operations on a milling machine.
- facemill
facemill
Milling cutter for cutting flat surfaces.
- facemilling
facemilling
Form of milling that produces a flat surface generally at right angles to the rotating axis of a cutter having teeth or inserts both on its periphery and on its end face.
- flat ( screw flat)
flat ( screw flat)
Flat surface machined into the shank of a cutting tool for enhanced holding of the tool.
- flutes
flutes
Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- milling
milling
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
- milling cutter
milling cutter
Loosely, any milling tool. Horizontal cutters take the form of plain milling cutters, plain spiral-tooth cutters, helical cutters, side-milling cutters, staggered-tooth side-milling cutters, facemilling cutters, angular cutters, double-angle cutters, convex and concave form-milling cutters, straddle-sprocket cutters, spur-gear cutters, corner-rounding cutters and slitting saws. Vertical cutters use shank-mounted cutting tools, including endmills, T-slot cutters, Woodruff keyseat cutters and dovetail cutters; these may also be used on horizontal mills. See milling.
- milling machine ( mill)
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
- milling machine ( mill)2
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
- profiling
profiling
Machining vertical edges of workpieces having irregular contours; normally performed with an endmill in a vertical spindle on a milling machine or with a profiler, following a pattern. See mill, milling machine.
- slotting
slotting
Machining, normally milling, that creates slots, grooves and similar recesses in workpieces, including T-slots and dovetails.
- toolholder
toolholder
Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.
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