1. Objectives
Use the nomenclature of a cutting-tool point
Explain the purpose of each type of rake and
clearance angle
Identify the applications of various types of
cutting-tool materials
Describe the cutting action of different types of
machines
29-1
2. 29-2
Cutting Tools
One of most important components in
machining process
Performance will determine efficiency of
operation
Two basic types (excluding abrasives)
Single point and multi point
Must have rake and clearance angles
ground or formed on them
3. Cutting-Tool Materials
Lathe toolbits generally made of five
materials
High-speed steel
Cast alloys (such as stellite)
Cemented carbides
Ceramics
Cermets
More exotic finding wide use
Borazon and polycrystalline diamond
29-3
4. Diamond Toolbits
Used mainly to machine nonferrous metals
and abrasive nonmetallics
Single-crystal natural diamonds
High-wear but low shock-resistant factors
Polycrystalline diamonds
Tiny manufactured diamonds fused together
and bonded to suitable carbide substrate
29-4
6. Cutting-Tool Nomenclature
Nose radius: radius to which nose is ground
Size of radius will affect finish
○ Rough turning: small nose radius (.015in)
○ Finish cuts: larger radius (.060 to .125 in.)
Point: end of tool that has been ground for
cutting purposes
29-6
10. Factors Affecting the Life of a
Cutting Tool
Type of material being cut
Microstructure of material
Hardness of material
Type of surface on metal (smooth or scaly)
Material of cutting tool
Profile of cutting tool
Type of machining operation being performed
Speed, feed, and depth of cut
29-10
14. Characteristics of a Good Cutting
Fluid
1. Good cooling 6. Rust
capacity resistance
2. Good lubricating 7. Nontoxic
qualities
8. Transparent
3. Resistance to
rancidity 9. Nonflammable
4. Relatively low
viscosity
5. Stability (long life)
34-14
15. Functions of a Cutting Fluid
Prime functions
Provide cooling
Provide lubrication
Other functions
Prolong cutting-tool life
Provide rust control
Resist rancidity
34-15
The side cutting edge angle is the angle the cutting edge forms with the side of the tool shank (Fig. 29-4). Side cutting angles for a general-purpose lathe cutting tool may vary from 10° to 20°, depending on the material cut. If this angle is too large (over 30°), the tool will tend to chatter. The end cutting edge angle is the angle formed by the end cutting edge and a line at right angles to the centerline of the toolbit (Fig. 29-4). This angle may vary from 5° to 30°, depending on the type of cut and finish desired. An angle of 5° to 15° is satisfactory for roughing cuts; angles between 15° and 30° are used for general-purpose turning tools. The larger angle permits the cutting tool to be swiveled to the left for taking light cuts close to the dog or chuck, or when turning to a shoulder. The side relief (clearance) angle is the angle ground on the flank of the tool below the cutting edge (Figs. 29-4 and 29-5). This angle is generally 6° to 10°. The side clearance on a toolbit permits the cutting tool to advance lengthwise into the rotating work and prevents the flank from rubbing against the workpiece. The end relief (clearance) angle is the angle ground below the nose of the toolbit, which permits the cutting tool to be fed into the work. It is generally 10° to 15° for general-purpose tools (Figs. 29-4 and 29-5). This angle must be measured when the toolbit is held in the toolholder. The end relief angle varies with the hardness and type of material and the type of cut. The end relief angle is smaller for harder materials, providing support under the cutting edge. The side rake angle is the angle at which the face is ground away from the cutting edge. For general-purpose toolbits, the side rake is generally 14° (Figs. 29-4 and 29-5). Side rake creates a keener cutting edge and allows the chips to flow away quickly. For softer materials, the side rake angle is generally increased. Side rake may be either positive or negative, depending on the material being cut. The angle of keennes s is the included angle produced by grinding side rake and side clearance on a toolbit (Fig. 29-4). This angle may be altered, depending on the type of material machined, and will be greater (closer to 90°) for harder materials. The back (top) rake angle is the backward slope of the tool face away from the nose. The back rake angle is generally about 20° and is provided for in the toolholder (Fig. 29-5). Back rake permits the chips to flow away from the point of the cutting tool. Two types of back or top rake angles are provided on cutting tools and are always found on the top of the toolbit: > Positive rake (Fig. 29-6a), where the point of the cutting tool and the cutting edge contact metal first and the chip moves down the face of the toolbit > Negative rake (Fig. 29-6b), where the face of the cutting tool contacts the metal first and the chip is forced up the face of the toolbit
