1. Mechanical Methods of Material Removal
Chapter 4
Chapter 4
IT 208

2. Competencies
Identify the unique characteristics associated with powered mechanical methods of material removal
Calculate the optimum feeds and speeds for milling, drilling and turning
List and define the two types of milling machine configurations
List the 3 major functions of cutting
Chapter 4
IT 208

3. Chapter 4
IT 208

4. POWERED MECHANICAL METHOD OF MATERIAL REMOVAL
Two most versatile
Lathe – to make cylindrical, conical, spherical, treaded shapes
Vertical mill – prismatic parts with contours with various shapes
Lathe Components
Bed- supports all other major components
Carriage- slides along the ways and consists of an assembly cross-slide, tool post, and apron.
Headstock- fixed to the bed and has motors, pulleys, and v-belts that supply power to the spindle (hollow) (work holding device attached to the spindle)
Tailstock- can slide along the ways and can be clamped down. Supports the part on the rear end with Live or Dead center6.
Feed rod and lead screw- used to provide power to the carriage to feed it along or across the work piece.
Chapter 4
IT 208

5. MATERIAL REMOVAL
4 Considerations that determine how fast to run a lathe:
Workpiece material
Tool diameter
Diameter of the work piece
Depth of cut
Chapter 4
IT 208

6. MATERIAL REMOVAL Cutting fluids- provide 3 major functions Lubrication
Cooling
Chip removal
Chapter 4
IT 208

7. MATERIAL REMOVAL
Milling- A process that is capable of producing a variety of configurations using a multitooth tool, turns the tool and holds the workpiece to provide the cutting action
Types of Milling Machines
Horizontal- the spindle is placed horizontal (used for heavier cutting)
Vertical- the spindle is placed vertical (the most common type of milling machine)
Chapter 4
IT 208

8. MATERIAL REMOVAL
Shaping and Planning - Cutting blades rotate while the material is passed through them.
Routing - Uses specially shaped cutting tool to remove material in a defined geometry.
Broaching - Specific file geometry is used to duplicate the profile of the broach inside a hole.
Drilling and Boring
Drilling - Stock is held stationary and the drill is rotated
Boring - Cutting tool is stationary and the material rotated
Chapter 4
IT 208

9. MATERIAL REMOVAL Reaming and Honing
Reamer- Similar to a drill, but has straight cutting edges and is used for finishing a hole to very close tolerances.
Hones - Small grindstone used to “move” material and smooth out the final surface.
Chapter 4
IT 208

10. MATERIAL REMOVAL Sawing
Advantages: Quick and cheap method of material removal
Disadvantages: Leaves rough surface on both sides of the cut.
Saw “Set” – Making the kerf wider than the blade backing so that the blade will not bind in the kerf.
Blade selection: Harder the material, the finer and closer the teeth. Steel t.p.i., Aluminum 8-12 t.p.i.
Circular Saws, Jig Saws, Hack Saws, Band, Saws, Chain Saws.
Abrasive Saws- used to cut (grind) extremely hard materials cannot be used to cut soft materials because it will “load” the blade.
Chapter 4
IT 208

11. MATERIAL REMOVAL Shearing and Punching
Shearing- Process of slitting flat stock up to ½” in thickness
Punching- Shearing any shaped hole in flat stock.
Grinding – Removal of material by abrasion.
“Dressing” a wheel is a process of using a diamond to remove the outer layer of a wheel, so that it becomes round (true) and the ends square.
Grit Size – refers to the size of grit that will pass through the number of openings per linear inch in a sieve. (i.e. 100 grit sand paper)
Chapter 4
IT 208

12. MATERIAL REMOVAL Cutting Tool Shapes (see fig. 4-50)
Side, back, and end rake angles are determined by the materials being cut and the type of cut being made. Hard materials require very little side or back rake angle.
High Speed Steel (HSS) – best choice for roughing purposes. They are inexpensive, can be easily resharpened, and are not extremely brittle. The HSS tools will take considerable shock. Their drawback is that they dull faster, especially in the cutting of harder metals.
Chapter 4
IT 208

13. MATERIAL REMOVAL
Carbide – Carbide tips will cut harder steels, but they are brittle and should not be used for roughing purposes. Carbide-tipped tools can produce closer tolerances and better finishes than the HSS tools.
Ceramic tools - are not affected by heat, and can be operated at extremely high revolutions per minute. However, these tools are similar to glass in brittleness. Ceramic tools are generally used only for the final, very light cut on very hard steels.
Chapter 4
IT 208

14. MATERIAL REMOVAL Feeds & Speeds
Cutting Speed – is the velocity of the surface of a workpiece as it passes the cutting tool.
Speed (SFPM) – given in surface feet per minute (SFPM).
Spindle Speed – is the rotational speed in revolutions per minute at which the lathe, milling machine, saw, grinder, or drill press is running.
Feed - the rate of advance of the cutting tool per revolution.
Depth of Cut – is the distance to which the cutting tool enters the workpiece.
Chapter 4
IT 208

15. MATERIAL REMOVAL Determining Optimum production
where N = spindle speed (rpm), CS = recommended SFPM, and D = diameter (ft)
Using recommended Cutting Speeds and Feeds Table 4.2 p.105
Chapter 4
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16. Problem
A 4-in.-diameter piece of mild, low-carbon steel is to be turned on a lathe using a carbide cutting tool. What is the optimum speed of the lathe? From table 2, Cs = 550 sfpm
Chapter 4
IT 208

17. Problem
A 0.5-in.-diameter hole is to be drilled in a piece of 316 stainless steel with a HSS drill. At what rpm should the drill press be set? From table 2, Cs= 100 sfpm
Chapter 4
IT 208

18. Problem
A lathe has a maximum speed of 1500 rpm. Could it be run at this maximum rpm using a carbide-tipped tool to cut a 2-in.-diameter piece of aluminum?
Yes, Cs = 1200 sfpm, Maximum recommended speed is 2292 RPM
Chapter 4
IT 208