1.5 PRACTICE PROBLEMS
1. Given that a tapered piece is to be made with the tailstock offset method, determine the taper per foot, and offset required if, you are starting with a bar of stock that is 8” long, and 1.125” in diameter, and the final taper is to be 6” long and 1” at the small end.
(ans. tpf = 0.25”, offset = 0.0833”)
2. Given the 1/2-12 UNC thread that is to be cut on the lathe,
a) What should the gear ratio between the machine spindle and the lead screw be if the lead screw is 5 t.p.i.?
b) What should the in-feed be for each pass?
3. Which of the following statements about lathe toolbits is correct?
a) a small nose radius will result in a smoother surface.
b) small relief angles will always increase friction.
c) large rake angles will decrease cutting forces.
d) none of the above.
(ans. c)
4. Which of the statements about lathes below is most correct?
a) jawed chucks hold only standard sizes of pieces.
b) mandrels hold work pieces from the outside.
c) the chasing dial is used for measuring fine cuts.
d) lead screws and feed rods are lathe parts
(ans. d)
5. When turning between centres a dog is required; what is a dog in this context?
(ans. it holds the work piece so that it can be driven with a face plate mounted on the lathe spindle)
6. A centre gauge (fish tail gauge) is employed in thread cutting. Suggest two uses for the gauge.
(ans. aligning a cutting tool for threads, )
7. Given an external 9/16-12-UNC thread, determined which tools would be used.
(ans. a turning tool to turn the outside diameter of 9/16”+1/12”, UNC tool to turn thread)
8. If we are rough cutting a 5” diameter bar of bronze on a lathe with a HSS tool,
a) what speed and feed should be used?
b) if the cut is 12” long, and will be made in two passes, how long will the operation take?
c) if the setup time is 5 minutes, and the machine rate is $50/hr., what will the cost of the operation be?
9. List the basic steps for setting up a lathe to cut a thread on a bar of stock, assume the stock is mounted between centres already.
(ans. see thread cutting section)
10. If a taper of 1mm in 10mm is to be cut, what will the offset distance be for a 10cm part?
11. Calculate the machine tool spindle speeds for the following,
a) turning on a lathe with a high speed steel tool in mild steel work with a diameter of 2.75”. The cutting speeds is 100 ft./min.
12. We have been given a mild steel bar that is to be turned on a lathe. It has a diameter of 14” and a length of 28”. We have been asked to make two rough passes, and one finishing pass. The tool we have selected is Carbide. When doing rough cuts we use a feed of 0.007”/rev., and for finishing cuts we use a feed of 0.004”/rev. How long will this operation take?
13. Which of the following statements about lathe toolbits is correct?
a) a small nose radius will result in a smoother surface.
b) small relief angles will always increase friction.
c) large rake angles will decrease cutting forces.
d) none of the above.
ans. C or D
14. Which of the statements about lathes below is most correct?
a) jawed chucks hold only standard sizes of pieces.
b) collets hold work pieces from the outside.
c) the chasing dial is used for measuring fine cuts.
d) lead screws and indexers are lathe parts
ans. B
15. Given the non-standard 3/8-19 UNC thread that is to be cut on the lathe,
a) What should the gear ratio between the machine spindle and the lead screw be if the lead screw is 4 t.p.i.?
b) What should the in-feed be for each pass?
ans. a) 4/19, b) 0.039
16. Develop a rough process plan for the part below by clearly listing operation steps in the correct sequence. Feeds, speeds, times and costs are not needed at this time.
ans.
17. The aluminum component below is to be turned on a lathe using a HSS tool. Develop a process plan, including offset for the taper, speeds, feeds, etc. Put the process plan in a list similar to the format shown. Assume a cost of $45.00/hr. for the lathe, and $25.00/hr. for all other pieces of equipment. State all assumption clearly, and justify numbers in the process plan with calculations or references.
18. On a lathe toolbit what are the functions of, a) the side relief angle, b) end relief angle, c) back rake, d) side rake angle, nose radius.
19. What applications are large positive rake angles for? negative rake angles?
20. What is the difference between end and face milling?
21. What RPM should be used to rough cut a cast iron piece with a 3” dia. with a high speed steel tool. What RPM should be used for a similar workpiece of plain carbon steel? What RPM should be used for the two materials if finishing cuts are being made?
22. Calculate the time required to machine a 2” dia. copper rod that is to be turned for a length of 10”.
23. What are rough and finish turning operations used for?
24. What are two methods for cutting stepped shoulders on a lathe?
25. Explain the difference between self holding and steep tapers using the coefficient of friction.
26. Find the tpf and tailstock offset for tapers on the following work.
a) D=1.5”, d=1.25”, TL=4”, OL=8”
27. convert a metric taper of 1:50 to a tpf. Convert a 1”tpf to metric.
28. Define the terms, fit, tolerance, allowance, limits, clearance, press fit, precision.
29. For a 1”-8-NC thread find the minimum and maximum diameters and minimum width of the toolbit point.
30. Describe the differences in speeds, feeds and depths of cuts for roughing and finishing cuts.
31. What types of chips are desirable when setting up automated cutting processes?
32. Compare the time to cut a work piece using a high speed steel tool and a carbide tool. The 4” dia. aluminum work is to be rough turned over a length of 14”.
33. What operations can be performed on a lathe?
34. How are the parameters different for a lathe when turning, as opposed to finishing?
35. A taper is to be cut on the aluminum part below. Indicate how far the tailstock should be offset and the speed and feed settings for the lathe.
(ans. offset=0.4”, feed 0.005-0.010”, speed 760RPM)
