Nine relief angle values have been described in ANSI B212.12-1991 standard. These angles are the difference from 90° measured in a plane normal to the cutting edge generated by the angle between the flank and top surface of the insert. Each relief angle is denoted by a capital letter as follows:

Edmund Isakov, Ph.D., is a consultant, writer and frequent CTE contributor. He is the author of the books “Mechanical Properties of Work Materials” (Modern Machine Shop Publications, 2000); “Engineering Formulas for Metalcutting” (Industrial Press, 2004); “Cutting Data for Turning of Steel” (Industrial Press, 2009); the CD-ROM “International System of Units (SI)” (Industrial Press, 2012); and the software “Advanced Metalcutting Calculators” (Industrial Press, 2005). For more information, call (561) 369-4063 or visit www.edmundisakovphd.com.

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Due to the magazine’s space limitations, the authors provide the following tables showing most popular Kennametal’s indexable inserts only for general turning of steel, cast iron, and nonferrous alloys. These tables don’t cover all Kennametal chip breakers. (Figure 4 and Figure 5 also show Kennametal Inc. insert identification system and chip breaker identification system respectively.)

According to ANSI B212.4-2002 standard, identification of the indexable insert includes 10 positions denoted by a capital letter. Each position (from 1 to 10) defines a characteristic of the insert in the following order:

On rectangular and parallelogram inserts, the width and length dimensions are used in place of the I.C. A two-digit number designates the sizes of these inserts. The first digit indicates the number of eighths of an inch in the width and the second digit indicates the number of fourths of an inch in the length of the insert.

If you cannot contact any contractor, calculate the cost of materials (for example, by going to the nearest construction store) and multiply this price by 2.5. You will obtain an approximate price including labor, assuming that 40% of the cost is taken by the materials and 60% by the labor.

For all other polygons, dimension B is the distance, measured along the bisector of the rounded off corner angle and a gage roll of nominal I.C. size tangent to the two sides opposite the corner (Figure 2). For example, if a tolerance letter is H, tolerances on dimensions (± from nominal) are: 0.0005" on dimension A, 0.0005" on dimension B and 0.001" on dimension T.

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Space provided behind a tool’s land or relief to prevent rubbing and subsequent premature deterioration of the tool. See land; relief.

In case of a facet, two letters are used. The first letter designates the facet angle: A – 45°; D – 60°; E – 75°; G – 87°; P – 90°; Z – Any other facet angle. The second letter designates the facet clearance angle:

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The sixth position is a significant one- or two-digit number indicating the number of sixteenths of an inch in the thickness of the insert. It is a one-digit number when the number of sixteenths of an inch in the thickness is a whole number: 1 – 1 ⁄ 16"; 2 – 1 ⁄ 8"; 3 – 3 ⁄ 16"; 4 – 1 ⁄ 4"; 5 – 5 ⁄ 16"; 6 – 3 ⁄ 8"; 7 – 7 ⁄ 16"; 8 – 1 ⁄ 2"; 9 – 9 ⁄ 16"; 10 – 5 ⁄ 8".

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The 10th position is only used if there are letters in the seventh position. It will be a significant number representing the nominal sixty-fourths of an inch in length of the primary facet: 1 – 1 ⁄ 64"; 2 – 1 ⁄ 32"; 3 – 3 ⁄ 64"; 4 – 1 ⁄ 16"; 5 – 5 ⁄ 64"; 6 – 3 ⁄ 32"; 7 – 7 ⁄ 64"; 8 – 1 ⁄ 8"; 9 – 9 ⁄ 64"; 10 – 5 ⁄ 32".

The fourth position is a capital letter denoting differences in design of insert, such as the existence of fixing holes, countersinks and special features on rake surfaces. There are 15 standard types in design as follows (Figure 3):

Once you know these values, you will be able to calculate the roof area. Begin by converting the roof pitch to an angle expressed in degrees using the following formulas:

1. Shape (e.g., A, C, D): 2. Clearance (e.g., A, B, C): 3. Tolerance Class (e.g., A, B, C): 4. Type (e.g., A, B, C): 5. Size Code: 6. Thickness Code: 7. Cutting-Point Configuration (e.g., 0, 0.5, A): 8. Edge Preparation (e.g., A, B, C): 9. Hand (R, L, N): 10. Facet Size: Decode Insert

Once you know the area of the roof, you have to decide on the scope of work. Do you want to build the roof from scratch or maybe replace the old layers? You also need to decide on the finishing material. For example, asphalt shingles will be less expensive than clay tiles.

ANSI B212.4-2002 standard added one more capital letter O, which denotes other relief angles for new designs of indexable inserts.

There are 14 tolerance classes that control the indexability of the inserts. Each class is denoted by a capital letter. Letters for tolerances are A, B, C, D, E, F, G, H, J, K, L, M, U and N.

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The seventh position indicates the cutting point configuration: a radius or a facet. In the case of a radius, the number indicates how many of 1 ⁄ 64 of an inch in the radius: 0 – sharp corner (0.002" max. radius); 0.2 – 0.004"; 0.5 – 0.008"; 1 – 1 ⁄ 64"; 2 – 1 ⁄ 32"; 3 – 3 ⁄ 64"; 4 – 1 ⁄ 16"; 5 – 5 ⁄ 64"; 6 – 3 ⁄ 32"; 7 – 7 ⁄ 64"; 8 – 1 ⁄ 8"; 10 – 5 ⁄ 32"; 12 – 3 ⁄ 16" 14 – 7 ⁄ 32" = 14; 16 – 1 ⁄ 4"; X – Any other corner radius.

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The roof area is 110.34 sq m. To arrive at this result, divide the house area by the cosine of the roof pitch: 100 / cos(25 deg) = 110.34.

Imaginary circle that touches all sides of an insert. Used to establish size. Measurements are in fractions of an inch and describe the diameter of the circle.

1. Shape2. Clearance3. Tolerance class4. Type5. Size6. Thickness7. Cutting-point configuration8. Edge preparation9. Hand10. Facet size

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Conditioning of the cutting edge, such as a honing or chamfering, to make it stronger and less susceptible to chipping. A chamfer is a bevel on the tool’s cutting edge; the angle is measured from the cutting face downward and generally varies from 25° to 45°. Honing is the process of rounding or blunting the cutting edge with abrasives, either manually or mechanically.

Tolerances on dimensions (± from nominal) are denoted by letters A, B and T. Dimension A is the nominal inscribed circle (I.C.) of the insert. Dimension T is the thickness of the insert. For pentagon, triangle and trigon shapes, dimension B is the insert height, i.e., the distance between one side and the opposite corner (Figure 2).

Tool that cuts a sloped depression at the top of a hole to permit a screw head or other object to rest flush with the surface of the workpiece.

About the Authors: Edmund Isakov, Ph.D., is a consultant, writer, and frequent CTE contributor. He is the author of four books “Mechanical Properties of Work Materials” (Modern Machine Shop Publications, 2000); “Engineering Formulas for Metalcutting” (Industrial Press, 2004); “Cutting Data for Turning of Steel” (Industrial Press, 2009); “International System of Units (SI)” the CD-ROM (Industrial Press, 2013); and the software “Advanced Metalcutting Calculators” (Industrial Press, 2005). For more information, call (561) 369-4063, or email: edmundisakov9701@comcast.net. Shi ‘Steve’ Chen is Manager Product Engineering Turning at Kennametal Inc. For more information, call (724) 539-5321, or email: Shi.Chen@Kennametal.com

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.

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After you've made all of these decisions, it's best to contact your local contractor and ask about the cost of both materials and labor per square meter or square foot of roof area. Remember that this unit price should include all additional elements such as fasteners, as well as the cost of removing all layers and disposing of them (if applicable).

The standard roof pitch is between 10 and 25 degrees. Choose a higher value (steeper roof) if you live in an area where it snows a lot: the snow will slide off the roof more easily.

Replaceable tool that clamps into a tool body, drill, mill or other cutter body designed to accommodate inserts. Most inserts are made of cemented carbide. Often they are coated with a hard material. Other insert materials are ceramic, cermet, polycrystalline cubic boron nitride and polycrystalline diamond. The insert is used until dull, then indexed, or turned, to expose a fresh cutting edge. When the entire insert is dull, it is usually discarded. Some inserts can be resharpened.

It will be a two-digit number carried to one decimal place when it is not a whole number: 1.2 – 5 ⁄ 32"; 1.5 – 3 ⁄ 16"; 1.8 – 7 ⁄ 32"; 2.5 – 5 ⁄ 16".

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The roofing calculator allows you to determine the area of the gable or shed roof of your house and to accurately estimate its cost. All you have to know are the dimensions of your house and the roof pitch, and this roof cost calculator will do the rest for you. Let's get started!

The last thing you have to do is to multiply this cost by your roof area and voilà, you now know the total cost of your roof! Remember that the real cost might differ from this value a bit due to waste, so plan ahead and assign more funds to this construction work.

There are 16 standard shapes of indexable inserts, and each shape is identified by a capital letter as follows (Figure 1):

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Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

Space provided behind the cutting edges to prevent rubbing. Sometimes called primary relief. Secondary relief provides additional space behind primary relief. Relief on end teeth is axial relief; relief on side teeth is peripheral relief.

The fifth position is a significant one- or two-digit number indicating the size of the inscribed circle (I.C.) for all inserts having a true I.C. such as Round, Square, Triangle, Trigon, Pentagon, Hexagon, Octagon, and Diamond. This position designates the number of eighths of an inch in the nominal size of the I.C. It will be a one-digit number when the number of eighths of an inch in the I.C. is a whole number: 1 – 1 ⁄ 8"; 2 – 1 ⁄ 4"; 3 – 3 ⁄ 8"; 4 – 1 ⁄ 2"; 5 – 5 ⁄ 8"; 6 – 3 ⁄ 4"; 7 – 7 ⁄ 8";

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Explanation: Enter each code position to decode the specific insert characteristics according to ANSI B212.4-2002 standards.

The mathematical expression denoting one of several parameters that describe surface texture (same as average roughness Ra). Average roughness is the arithmetic average height deviation of the measured surface profile from the profile centerline. See surface texture.

American National Standard ANSI B212.4-2002 covers the identification system for indexable-type inserts for both single-point and multiple-point cutting tools. It was published on October 29, 2002. The earlier editions of the standard are:

It is a two-digit number carried to one decimal place when it is not a whole number: 1.2 – 5 ⁄ 64"; 1.5 – 3 ⁄ 32"; 2.5 – 5 ⁄ 32"; 3.5 – 7 ⁄ 32".

The most typical cost of roofing falls between $2 and $4 per square foot (including labor). If the price proposed by your contractor deviates from these values, it is advisable to check with other contractors before starting the work.

Inserts selection depends on workpiece material, chip control, surface finish, tool life, and the machine tool’s power and torque requirements. One of the commonly used indexable inserts for general turning is CNMG 432.