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The side-and-face cutter is designed with cutting teeth on its side as well as its circumference. They are made in varying diameters and widths depending on the application. The teeth on the side allow the cutter to make unbalanced cuts (cutting on one side only) without deflecting the cutter as would happen with a slitting saw or slot cutter (no side teeth).

There are several common standardized methods of mounting shell mills to their arbors. They overlap somewhat (not entirely) with the analogous joining of lathe chucks to the spindle nose.

While it is best to consult with a blade manufacturer or supplier to determine the optimal blade for an application, some general guidelines are helpful.

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

For softer materials, such as carbon steel and aluminum, adjust the feed to 50% of the normal rate for the first 50 to 100 sq. in. Then, gradually increase the feed rate to 100%, he suggested.

1. Soluble oil cutting fluids become an emulsion when mixed with water. These have effective heat transfer properties and offer good lubrication. They are popular because they are inexpensive.

There are 8 cutters (excluding the rare half sizes) that will cut gears from 12 teeth through to a rack (infinite diameter).

Most fly cutters simply have a cylindrical center body that holds one tool bit. It is usually a standard left-hand turning tool that is held at an angle of 30 to 60 degrees. Fly cutters with two tool bits have no "official" name but are often called double fly cutters, double-end fly cutters, or fly bars. The latter name reflects that they often take the form of a bar of steel with a tool bit fastened on each end. Often these bits will be mounted at right angles to the bar's main axis, and the cutting geometry is supplied by using a standard right-hand turning tool.

Teeth on new bandsaw blades have very sharp edges, which easily can be chipped unevenly or destroyed if run at full speed with full feed pressure on the initial cuts and not broken in properly.  Image courtesy of L.S. Starrett

Wide material requires a hard rake as the chips will be larger than those produced when sawing narrow material. The “set” refers to the pattern in which the teeth bend away from the centerline of the blade to create space for it to fit through the cut slot. In an alternate set, every other tooth is bent the same direction away from the centerline, and the other half of the teeth are bent the opposite direction away from the centerline. In a raker set, some teeth are not bent outward but left in the center to rake waste out of the cut. In general, raker sets are used with aggressive cutting blades.

Blade speed, which typically is measured in sfm, refers to the speed at which a blade travels around the guide wheel. Harder metals, such as steel, require a slower blade speed than softer materials, such as aluminum, to achieve a smooth cut.

Selecting a milling cutter is not a simple task. There are many variables, opinions and lore to consider, but essentially the machinist is trying to choose a tool that will cut the material to the required specification for the least cost. The cost of the job is a combination of the price of the tool, the time taken by the milling machine, and the time taken by the machinist. Often, for jobs of a large number of parts, and days of machining time, the cost of the tool is lowest of the three costs.

A shell mill is any of various milling cutters (typically a face mill or endmill) whose construction takes a modular form, with the shank (arbor) made separately from the body of the cutter, which is called a "shell" and attaches to the shank/arbor via any of several standardized joining methods.

Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations (and occasionally in other machine tools). They remove material by their movement within the machine (e.g., a ball nose mill) or directly from the cutter's shape (e.g., a form tool such as a hobbing cutter).

“Typically, a variable rake is used for cutting at a slow rate,” Goldsmith said. “A ‘hard’ rake has a larger angle, allowing more room for chip formation. A ‘soft’ rake has a narrower angle with less room for chip formation.”

Cutter location is the topic of where to locate the cutter in order to achieve the desired contour (geometry) of the workpiece, given that the cutter's size is non-zero. The most common example is cutter radius compensation (CRC) for endmills, where the centerline of the tool will be offset from the target position by a vector whose distance is equal to the cutter's radius and whose direction is governed by the left/right, climb/conventional, up/down distinction. In most implementations of G-code, it is G40 through G42 that control CRC (G40 cancel, G41 left/climb, G42 right/conventional). The radius values for each tool are entered into the offset register(s) by the CNC operator or machinist, who then tweaks them during production in order to keep the finished sizes within tolerance. Cutter location for 3D contouring in 3-, 4-, or 5-axis milling with a ball-endmill is handled readily by CAM software rather than manual programming. Typically the CAM vector output is postprocessed into G-code by a postprocessor program that is tailored to the particular CNC control model. Some late-model CNC controls accept the vector output directly, and do the translation to servo inputs themselves, internally.

These images show a saw blade before and after the break-in process. The rough edges in the top image are realigned in the bottom image. Images courtesy of Kaast Machine Tools

A face mill is a cutter designed for facing as opposed to e.g., creating a pocket (end mills). The cutting edges of face mills are always located along its sides. As such it must always cut in a horizontal direction at a given depth coming from outside the stock. Multiple teeth distribute the chip load, and since the teeth are normally disposable carbide inserts, this combination allows for very large and efficient face milling.

Ball nose cutters or ball end mills (lower row in image) are similar to slot drills, but the end of the cutters are hemispherical. They are ideal for machining 3-dimensional contoured shapes in machining centres, for example in moulds and dies. They are sometimes called ball mills in shop-floor slang, despite the fact that that term also has another meaning. They are also used to add a radius between perpendicular faces to reduce stress concentrations.

These cutters are a type of form tool and are used in hobbing machines to generate gears. A cross-section of the cutter's tooth will generate the required shape on the workpiece, once set to the appropriate conditions (blank size). A hobbing machine is a specialised milling machine.

Tendency of all metals to become harder when they are machined or subjected to other stresses and strains. This trait is particularly pronounced in soft, low-carbon steel or alloys containing nickel and manganese—nonmagnetic stainless steel, high-manganese steel and the superalloys Inconel and Monel.

The history of milling cutters is intimately bound up with that of milling machines. Milling evolved from rotary filing, so there is a continuum of development between the earliest milling cutters known, such as that of Jacques de Vaucanson from about the 1760s or 1770s,[3][4] through the cutters of the milling pioneers of the 1810s through 1850s (Whitney, North, Johnson, Nasmyth, and others),[5] to the cutters developed by Joseph R. Brown of Brown & Sharpe in the 1860s, which were regarded as a break from the past[6][7] for their large step forward in tooth coarseness and for the geometry that could take successive sharpenings without losing the clearance (rake, side rake, and so on). De Vries (1910)[7] reported, "This revolution in the science of milling cutters took place in the States about the year 1870, and became generally known in Europe during the Exhibition in Vienna in 1873. However strange it may seem now that this type of cutter has been universally adopted and its undeniable superiority to the old European type is no longer doubted, it was regarded very distrustfully and European experts were very reserved in expressing their judgment. Even we ourselves can remember that after the coarse pitched cutter had been introduced, certain very clever and otherwise shrewd experts and engineers regarded the new cutting tool with many a shake of the head. When[,] however, the Worlds Exhibition at Philadelphia in 1876, exhibited to European experts a universal and many-sided application of the coarse pitched milling cutter which exceeded even the most sanguine expectations, the most far-seeing engineers were then convinced of the immense advantages which the application of the new type opened up for the metalworking industry, and from that time onwards the American type advanced, slowly at first, but later on with rapid strides".[8]

This modular style of construction is appropriate for large milling cutters for about the same reason that large diesel engines use separate pieces for each cylinder and head whereas a smaller engine would use one integrated casting. Two reasons are that (1) for the maker it is more practical (and thus less expensive) to make the individual pieces as separate endeavors than to machine all their features in relation to each other while the whole unit is integrated (which would require a larger machine tool work envelope); and (2) the user can change some pieces while keeping other pieces the same (rather than changing the whole unit). One arbor (at a hypothetical price of USD100) can serve for various shells at different times. Thus 5 different milling cutters may require only USD100 worth of arbor cost, rather than USD500, as long as the workflow of the shop does not require them all to be set up simultaneously. It is also possible that a crashed tool scraps only the shell rather than both the shell and arbor. To also avoid damage to the shell, many cutters, especially in larger diameters, also have another replaceable part called the shim, which is mounted to the shell and the inserts are mounted on the shim. That way, in case of light damage, only the insert and maximum the shim needs replacement. The shell is safe. This would be like crashing a "regular" endmill and being able to reuse the shank rather than losing it along with the flutes.

The process to break in a bandsaw blade varies depending on the characteristics of the workpiece material, said Jay Gordon, North American sales manager of saws and hand tools at L.S. Starrett. When breaking in a blade, users should run the machine at the normal blade speed.

4. Semisynthetic fluids are a mix of synthetic and soluble fluids and share some of their characteristics. Semisynthetics are cheaper than synthetics. Insufficiently or overly diluted coolant can result in production of foam, inadequate chip removal or a lack of cooling during the cut.

Slab mills are used either by themselves or in gang milling operations on manual horizontal or universal milling machines to machine large broad surfaces quickly. They have been superseded by the use of cemented carbide-tipped face mills which are then used in vertical mills or machining centres.

The most common type of joint between shell and arbor involves a fairly large cylindrical feature at center (to locate the shell concentric to the arbor) and two driving lugs or tangs that drive the shell with a positive engagement (like a dog clutch). Within the central cylindrical area, one or several socket head cap screws fasten the shell to the arbor.

A bull nose cutter mills a slot with a corner radius, intermediate between an end mill and ball cutter; for example, it may be a 20 mm diameter cutter with a 2 mm radius corner. The silhouette is essentially a rectangle with its corners truncated (by either a chamfer or radius).

Hollow milling has an advantage over other ways of cutting because it can perform multiple operations. A hollow mill can reduce the diameter of a part and also perform facing, centering, and chamfering in a single pass.

Once teeth are honed and broken in, a blade will cut faster and straighter and last longer than an incorrectly broken-in blade. Following a proper break-in process is a simple, easy way to ensure maximum productivity in a sawing operation.

Both convex and concave spherical radii are possible with a hollow mill. The multiple blades of a hollow mill allow this radius to be produced while holding a tight tolerance.

This process allows a blade to travel through the guides and become aligned correctly for cutting. Also, this increases the temperature of the blade, which permits imperfections in the material to bend instead of breaking blade teeth. The warming—followed by natural, inherent cooling—helps strengthen the blade substrate.

Another type of shell fastening is simply a large-diameter fine thread. The shell then screws onto the arbor just as old-style lathe chuck backplates screw onto the lathe's spindle nose. This method is commonly used on the 2" or 3" boring heads used on knee mills. As with the threaded-spindle-nose lathe chucks, this style of mounting requires that the cutter only make cuts in one rotary direction. Usually (i.e., with right-hand helix orientation) this means only M03, never M04, or in pre-CNC terminology, "only forward, never reverse". One could use a left-hand thread if one needed a mode of use involving the opposite directions (i.e., only M04, never M03).

The rake refers to the tooth shape, specifically the angle of the cutting end of the tooth. Most bandsaw blade teeth have a 0° rake or slight positive rake. The more positive the rake is, the more aggressive the blade cuts. A positive angle increases the tilt of the tooth face and is best suited for heavy-wall tubing and thick solids. Straight or less positive rakes are preferred for bundle and structural cutting. A variable rake indicates that teeth are set to different entry angles, resulting in different amounts of material removed by each tooth.

Whereas a hob engages the work much as a mating gear would (and cuts the blank progressively until it reaches final shape), a thread milling cutter operates much like an endmill, traveling around the work in a helical interpolation.

Woodbury provides citations[9] of patents for various advances in milling cutter design, including irregular spacing of teeth (1867), forms of inserted teeth (1872), spiral groove for breaking up the cut (1881), and others. He also provides a citation on how the introduction of vertical mills brought about wider use of the endmill and fly cutter types.[10]

The service life of a bandsaw blade and the quality of the imparted surface finish are not determined solely by the product design from a blade manufacturer. Machine maintenance and operating practices can impact performance.

Regular fly cutters (one tool bit, swept diameter usually less than 100 mm) are widely sold in machinists' tooling catalogs. Fly bars are rarely sold commercially; they are usually made by the user. Fly bars are perhaps a bit more dangerous to use than endmills and regular fly cutters because of their larger swing. As one machinist put it, running a fly bar is like "running a lawn mower without the deck",[2] that is, the exposed swinging cutter is a rather large opportunity to take in nearby hand tools, rags, fingers, and so on. However, given that a machinist can never be careless with impunity around rotating cutters or workpieces, this just means using the same care as always except with slightly higher stakes. Well-made fly bars in conscientious hands give years of trouble-free, cost-effective service for the facing off of large polygonal workpieces such as die/mold blocks.

The machinist needs three values: S, F and Depth when deciding how to cut a new material with a new tool. However, he will probably be given values of Vc and Fz from the tool manufacturer. S and F can be calculated from them:

“When you first remove the pencil from the sharpener, it will take only the slightest amount of pressure to inadvertently break that point right off at the tip,” said Richard Klipp, president of Morgantown, Pennsylvania-based Behringer Saws Inc. “However, after a few minutes of writing, the point becomes less sharp and ultimately less susceptible to breakage.”

A fly cutter is composed of a body into which one or two tool bits are inserted. As the entire unit rotates, the tool bits take broad, shallow facing cuts. Fly cutters are analogous to face mills in that their purpose is face milling and their individual cutters are replaceable. Face mills are more ideal in various respects (e.g., rigidity, indexability of inserts without disturbing effective cutter diameter or tool length offset, depth-of-cut capability), but tend to be expensive, whereas fly cutters are very inexpensive.

Blade pitch, defined as the number of teeth per inch, must be selected, O’Loughlin said. The number of teeth that contact a workpiece can affect blade performance and durability. Too many or too few teeth can cause strippage, especially when the feed rate or speed is too high or low.

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Yesenia Duran is a Chicago-based freelance journalist who covers cutting tools and technology. She can be reached at sennyx@gmail.com.

Users should consult a machine manufacturer for the best blade width, except for contour cutting in vertical machines when a chart can be referenced.  As for blade length, it varies according to the bandsaw machine type and specifications. The correct blade length should be shown in the bandsaw machine user manual.

End mills (middle row in image) are those tools that have cutting teeth at one end, as well as on the sides. The words end mill are generally used to refer to flat bottomed cutters, but also include rounded cutters (referred to as ball nosed) and radiused cutters (referred to as bull nose, or torus). They are usually made from high speed steel or cemented carbide, and have one or more flutes. They are the most common tool used in a vertical mill.

Cutters of this form factor were the earliest milling cutters developed. From the 1810s to at least the 1880s they were the most common form of milling cutter, whereas today that distinction probably goes to end mills. Traditionally, HSS side and face cutters are used to mill slots and grooves.

Also known as down feed, feed pressure represents the amount of force that pushes a blade into material. Feed pressure can be static or adjustable, dependent on the machine being run, and is set by the saw operator.

Hollow mills offer an advantage over single point tooling. Multiple blades allow the feed rate to double and can hold a closer concentricity. The number of blades can be as many as 8 or as few as 3.  For significant diameter removal (roughing), more blades are necessary.

“Some feel it is not worthwhile enough to slow down the cutting operation to break in a blade,” said Tim O’Loughlin, saws and hand tools product manager at The L.S. Starrett Co., Athol, Massachusetts. “However, while the break-in process does involve reducing the feed pressure for the first 25 to 100 sq. in. of cutting, the extra time is compensated many times over in the extended life span of the blade, in addition to the resulting improved surface finish in the cuts.”

Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.

Managers at machine shops with saws closely monitor downtime associated with blade changes due to wear or breakage and spend a considerable amount of time and energy finding ways to increase efficiency.

Saw specialists agree that a broken-in blade should see significantly increased service life yet concede that users may have different perspectives.

Using a high-quality metalcutting fluid is necessary to extend the life of a saw blade. Also, ensure that fluid is mixed in the ratio required for a job. This common sawing problem is avoided easily.

Trepanning is also possible with a hollow mill. Special form blades can be used on a hollow mill for trepanning diameters, forms, and ring grooves.

Although there are many different types of milling cutter, understanding chip formation is fundamental to the use of any of them. As the milling cutter rotates, the material to be cut is fed into it, and each tooth of the cutter cuts away a small chip of material. Achieving the correct size of chip is of critical importance. The size of this chip depends on several variables.

Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).

An adjustable hollow mill is a valuable tool for even a small machine shop to have because the blades can be changed out for an almost infinite number of possible geometries.

3. Straight oils are not diluted or water-soluble. These are made with an oil base and sometimes contain fat and vegetable oils, as well as sulfur and chlorine. Oil-based products present the best lubrication but the worst cooling when compared with other fluids.

Most shell mills made today use indexable inserts for the cutting edges—thus shank, body, and cutting edges are all modular components.

A common use of a hollow mill is preparing for threading.  The hollow mill can create a consistent pre-thread diameter quickly, improving productivity.

More advanced hollow mills use indexable carbide inserts for cutting, although traditional high speed steel and carbide-tipped blades are still used.

Scientific study by Holz and De Leeuw of the Cincinnati Milling Machine Company[11] made the teeth even coarser and did for milling cutters what F.W. Taylor had done for single-point cutters with his famous scientific cutting studies.

Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

Machine that utilizes an endless band, normally with serrated teeth, for cutoff or contour sawing. See saw, sawing machine.

Hollow milling cutters, more often called simply hollow mills, are essentially "inside-out endmills". They are shaped like a piece of pipe (but with thicker walls), with their cutting edges on the inside surface. They were originally used on turret lathes and screw machines as an alternative to turning with a box tool, or on milling machines or drill presses to finish a cylindrical boss (such as a trunnion). Hollow mills can be used on modern CNC lathes and Swiss style machines. An advantage to using an indexable adjustable hollow mill on a Swiss-style machine is replacing multiple tools.  By performing multiple operations in a single pass, the machine does not need as can accommodate other tools in the tool zone and improves productivity.

Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

Interpolation is also not necessary when using a hollow mill; this can result in a significant reduction of production time.

“Typically, blades need to be run with break-in in mind for two to three hours,” said Ebony Goldsmith, office manager and bandsaw specialist at Aldan, Pennsylvania-based Kaast Machine Tools Inc. “A blade that is not broken in will likely only last about an hour. A properly broke-in blade should last 100 to 150 hours.”

For example, too many teeth per inch can greatly reduce the cutting speed and ultimately make material impossible to cut. At a lower cutting speed, there is less penetration per tooth, causing more rubbing than cutting, which can result in substantial workhardening of material and strip the teeth. Workhardening also is compounded by an inability to evacuate chips because gullets load up more easily in fine-pitch blades, increasing friction.

Another important quality of the milling cutter to consider is its ability to deal with the swarf generated by the cutting process. If the swarf is not removed as fast as it is produced, the flutes will clog and prevent the tool cutting efficiently, causing vibration, tool wear and overheating. Several factors affect swarf removal, including the depth and angle of the flutes, the size and shape of the chips, the flow of coolant, and the surrounding material. It may be difficult to predict, but a good machinist will watch out for swarf build up, and adjust the milling conditions if it is observed.

The sawing process has many variables, including the choice of blade for the job at hand, the selected feed rate and cutting speed, the rake angle and how a saw is broken in.

Machining operation in which a powered machine, usually equipped with a blade having milled or ground teeth, is used to part material (cutoff) or give it a new shape (contour bandsawing, band machining). Four basic types of sawing operations are: hacksawing (power or manual operation in which the blade moves back and forth through the work, cutting on one of the strokes); cold or circular sawing (a rotating, circular, toothed blade parts the material much as a workshop table saw or radial-arm saw cuts wood); bandsawing (a flexible, toothed blade rides on wheels under tension and is guided through the work); and abrasive sawing (abrasive points attached to a fiber or metal backing part stock, could be considered a grinding operation).

Angle of inclination between the face of the cutting tool and the workpiece. If the face of the tool lies in a plane through the axis of the workpiece, the tool is said to have a neutral, or zero, rake. If the inclination of the tool face makes the cutting edge more acute than when the rake angle is zero, the rake is positive. If the inclination of the tool face makes the cutting edge less acute or more blunt than when the rake angle is zero, the rake is negative.

Milling cutters come in several shapes and many sizes. There is also a choice of coatings, as well as rake angle and number of cutting surfaces.

Consider whether constant or variable pitch is better. With constant pitch, which is typically for general-purpose sawing, all teeth on a blade have uniform spacing, gullet depths and rake angles throughout the full length. Variable-pitch teeth have varying teeth sizes and gullet depths to substantially reduce noise levels and vibrations. The latter cuts all structurals, tubing and solids smoothly and quickly.

Roughing end mills quickly remove large amounts of material. This kind of end mill utilizes a wavy tooth form cut on the periphery. These wavy teeth act as many successive cutting edges producing many small chips. This results in a relatively rough surface finish, but the swarf takes the form of short thin sections and is more manageable than a thicker more ribbon-like section, resulting in smaller chips that are easier to clear. During cutting, multiple teeth are in simultaneous contact with the workpiece, reducing chatter and vibration. Rapid stock removal with heavy milling cuts is sometimes called hogging. Roughing end mills are also sometimes known as "rippa" or "ripper" cutters.

A constant-pitch blade can increase harmonic vibrations. This design may lead to excessive noise, undesirable saw or saw blade vibrations and, in severe cases, poor-quality cuts. When considering tooth pitch for blades, variable-pitch blades can vastly decrease harmonic vibrations. By varying tooth spacing, sawing rhythms are interrupted, chip evacuation improves and vibration abates, resulting in less noise and a better overall cut.

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2. Synthetic fluids do not contain oil-based products and are made from compounds. Normally diluted when used, synthetics include additives that prevent corrosion. The fluids provide the best cooling when compared with other fluids but are expensive.

Saws themselves shouldn’t need to be broken in, but blades do. Breaking in a bandsaw blade essentially means honing each tooth to form a microfine radius. This smoothing removes microscopic rough edges, which could rip off and cause tiny imperfections at the tip of each tooth as a result.

For difficult-to-cut materials, such as nickel-base alloys, hardened steel, tool steel and stainless, adjust the feed rate to 75% of the normal cutting rate for the first 25 to 75 sq. in. Gradually increase the feed rate to reach 100% after 50 sq. in. As the feed increases to the 100% rate, be careful not to create unwanted vibrations by increasing the rate too quickly.

Feed rate is the speed at which material is removed by the teeth of a blade, usually listed as square ipm. The rate is determined by the material being cut, the blade used and the blade speed.

He said the same holds true for a saw blade. Right out of the box, a saw blade tip is very sharp and more susceptible to damage, such as a broken tooth, than after being used for a short period. Blade suppliers therefore often recommend running at a reduced down feed rate—usually 20% to 50% of the suggested rate—until tips are broken in. Afterward, the feed can be set at the recommended rate.