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
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
29-2
Cutting-Tool Materials
Lathe toolbits generally made of five materialsHigh-speed steelCast alloys (such as stellite)Cemented carbidesCeramicsCermets
More exotic finding wide useBorazon and polycrystalline diamond
29-3
Diamond Toolbits
Used mainly to machine nonferrous metals and abrasive nonmetallics
Single-crystal natural diamondsHigh-wear but low shock-resistant factors
Polycrystalline diamondsTiny manufactured diamonds fused together
and bonded to suitable carbide substrate
29-4
Cutting-Tool Nomenclature
Cutting edge: leading edge of that does cutting
Face: surface against which chip bears as it is separated from work
Nose: Tip of cutting tool formed by junction of cutting edge and front face
29-5Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cutting-Tool Nomenclature
Nose radius: radius to which nose is groundSize 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
Lathe Toolbit Angles and Clearances
29-7
Lathe Cutting-tool Angles
29-8
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Positive rake: point of cutting tool and cutting edgecontact metal first and chipmoves down the face ofthe toolbit
Negative rake: face of cutting tool contacts metal first and chip moves up the face of the toolbit
Tool Life
29-9
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Occurs on side of cuttingedge as result of friction
between side of cutting-tooledge and metal being
machined
When flank wear is .015 to .030 in.need to be reground
Nose wear occursas result of friction betweennose and metal being machined
Crater wear occurs as resultof chips sliding along chip-tool interface,result of built-upedge on cuttingtool
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
Turning
29-11
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Assume cutting machine steel: If rake and relief clearanceangles correct and proper speed and feed used, a continuouschip should be formed.
29-12
Nomenclature of a Plain Milling Cutter
Nomenclature of an End Mill
29-13Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Characteristics of a Good Cutting Fluid
1. Good cooling capacity
2. Good lubricating qualities
3. Resistance to rancidity
4. Relatively low viscosity
5. Stability (long life)
6. Rust resistance
7. Nontoxic8. Transparent9. Nonflammable
34-14
Functions of a Cutting Fluid
Prime functionsProvide coolingProvide lubrication
Other functionsProlong cutting-tool lifeProvide rust controlResist rancidity
34-15
Milling
Face millingRing-type distributor recommended to flood
cutter completelyKeeps each tooth of cutter immersed in cutting
fluid at all times Slab milling
Fluid directing to both sides of cutter by fan-shaped nozzles ¾ width of cutter
34-16
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