Lathe Machine

1. What two measurement are used to indicate the size of a lathe ?
Two measurements used to indicate the size of a lathe is the swing of lathe (in inches) and the total length between the centers, with the tailstock at the end of the ways.


2. In what common size range are most of the lathes used in industry ?
10 to 30 inches (254 to 762mm) diameter swing.


3. Why is the important to protect the ways of a lathe ? How should they be protected ?
It is important to protect the ways of the lathe in order to ensure their precision ; Ways determine the straightness of movement of carriage assembly . The Ways should be covered when machining materials such as wood , phenolic , rubber , and other abrasive materials. Oil the ways for further protection and to enable the carriage assembly to move about easily.

4. Explain the major differences between the feed rod and lead screw?
The feed rod moves the carriage during turning , boring , and facing operation ; The lead screw advances the carriage during threading operations


5. List the advantages and disadvantages of the following cutting tools:
advantages
disadvantages

a)High-speed steel
-cheap
-hard
-high heat resistance
-easy to reground
-high cutting speed
-low withstand shock

b)Cast alloys
-hard
-reharden without treatment
-high cutting speed
-brittle
-difficult to grind

c)Cemented carbides
-hard
-high cutting speed
-available in variety of shape and size
-careful consideration needed when using

d)Oxides
-low heat conductivity
-high compressive strength
-high resistance to abrasive wear
-high cutting speed
-brittle

6. Explain the following terms
(a) Face-the top of a toolbit and is the surface where the chip passes as it is cut away from the workpiece .
(b) Cutting edge-the part of the toolbit that does the actual cutting of the workpiece .
(c) Flank-the surface directly below the cutting edge .
(d) Nose-the tip of the toolbit and is formed by the side and end edges .
(e) Base-the bottom surface of the tool .

7. Calculate the proper rpm rate for the following situations:
a. rpm= 12 x 200 / (3.1416 x 1 ¾)
= 24 / (5.4978)
= 437
b. rpm=12 x 84 / (3.1416 x 6 1/8)
= 1008 / (19.24)
= 52
c. rpm= 40 / (3.1416 x 0.025)
= 509
d. rpm= 19 / (3.1416 x 0.0127)
= 476

8. What feed rates are generally used for roughing and finishing cuts?
Depend on the machines and materials used.

9. Why is facing done on a workpiece?
Facing is done on a lathe to square the ends of a workpiece

10. Define straight and taper turning operation .
a)Straight turning operation –performed upon a workpiece supported in a chuck, but the majority of workpieces turned on an engine lathe are turned between centers. Turning is the removal of metal from the external surface of cylindrical workpieces using various types of cutter toolbits. As a rule, the workpiece is turned down by a number of roughing cuts to a predetermined diameter which is within 1/32 to 1/64 inch of the diameter desired. The remaining metal is removed by a finish cut using a fine fed to produce a good surface. After taking the first roughing cut along the entire workpiece surface check the center alignment by measuring each end with calipers. If the ends are of different diameters, the tailstock center is out of alignment with the headstock spindle and realignment is necessary. Continue cutting after correct alignment is made, stopping the lathe at intervals to check the tailstock center. After roughing, reverse the ends of the workpiece so that the area held by the lathe dog can be turned. When the piece is within 1/32 to 1/64 inch of the desired size, reduce the depth of cut, reduce the feed, increase the speed, and take light finishing cuts to the proper dimension. Measure the workpiece after each cut, with micrometer calipers. Reverse the piece again and, using shims under the lathe dog to prevent scoring of the machined surface, finish the other end of the workpiece.
b)Taper turning operation-the tool moves at a angle to the axis of the work, producing a taper. Therefore, to turn a taper, the work must either be mounted in a lathe so that the axis upon which it turns is at an angle to the axis of the lathe, or cause the cutting tool to move at an angle to the axis of the lathe. When the diameter of a piece changes uniformly, from one end to the other, the piece is said to be tapered. Taper turning as a machining operation is the gradual reduction in diameter from one part of a cylindrical workpiece to another part . Tapers can be either external or internal. If a workpiece is tapered on the outside, it has an external taper; if it is tapered on the inside, it has an internal taper . The method used for turning a taper depends on the degree, length, location of the taper (internal or external), and the number of pieces to be done. The three basic methods of turning a taper require the operator to use either a compound rest, offset the tailstock, or use the taperattachment. With any of these methods, the cutting tool must be set exactly on and the rate of taper will vary with each cut.

11. Explain the difference between roughing and finishing cuts .
a)Roughing cut – removes the majority of material from the workpiece , leaving enough metal for the final or finishing cut .
b)Finishing cut –are use to make the surface smooth and accurate .

12. What is the backlash ? How can backlash influence tool settings ?
Backlash is the play or clearance between the cross feed screw and nut assembly . Backlash influence exactness tool settings when the turning operation is carried on. Accurate tool settings are accomplished by always feeding the tool toward the workpiece on successive cuts.