## 4.12 Practice Problems

1. What would happen if a drill without flutes was used?

2. If we want a hole with a 1/2-14-UNC thread, what size of tap drill should be used?

3. What type of drill press is suitable for drilling holes in car engine blocks? Justify your answer.

4. Which of these statements is not correct?

a) work is not moved on a radial arm drill press.

b) automatic feeds are available on sensitive drill presses.

c) multispindle drill presses always drill multiple holes at once.

d) all of the above.

5. Which of these statements is correct?

a) a margin of a drill bit does most of the cutting.

b) the relief angle on the tip of the drill bit makes it not a conical shape.

c) a large drill bit point angle is useful for cutting soft materials.

d) none of the above.

6. Which of the following statements is not correct?

a) core drills have 3 or 4 flutes.

b) high helix drills help in chip removal.

c) straight fluted drills are used for sheet metal.

d) centre drills are for long holes, such as gun barrels.

7. Which of the following is not a typical drill press operation?

a) counter boring.

b) spot facing.

c) counter sinking.

d) none of the above.

8. Which of the statements is most correct?

a) reamers are used to finish holes with accuracies not possible when a normal drill is used.

c) taps and reamers can both be used without a machine tool.

d) none of the above.

9. Given a hole that is to be drilled then reamed to 3.000”, develop a process plan including speeds and feeds.

10. We want to drill a hole that is 2.369” in diameter. If we know that the accuracy the shop can provide for drilling is +0.030” to -0.010”,

a) what is an appropriate fractional drill size to use?

b) what operation might follow?

11. Calculate the machine tool spindle speeds for the following,

a) drilling with a 19/32” high speed steel bit in mild steel. The CS is 70 ft./min.

12. We are to drill 6 holes in a 2” thick mild steel plate. The plate is held in a jig. We are using a 63/64” high speed steel drill, and the suggested parameters are CS = 80 ft./min. with a feed of 0.004”/rev. After drilling each hole is to be finished with a 1.0” diameter reamer. If the suggested parameters for the reamer are CS = 80 ft./min. with a feed of 0.010”/rev.,

a) calculate the time to do all of the operations (and make allowances for drill point travel)

b) find the cost to produce 500 parts when each part needs 3 minutes for setup (no operation), labor rates are \$25/hr., and overhead is \$25/hr.

13. Which of these statements is not correct?

a) work is not moved on a radial arm drill press.

b) automatic feeds are available on sensitive drill presses.

c) multispindle drill presses must always drill multiple holes at once.

d) all of the above.

ans. B

14. Which of these statements is correct?

a) a margin of a drill bit does most of the cutting.

b) the relief angle on the tip of the drill bit makes it a conical shape.

c) a large drill bit point angle is useful for cutting soft materials.

d) none of the above.

ans. D

15. Which of the following statements is not correct?

a) core drills have a hollow center to remove chips.

b) high helix drills help in chip removal.

c) straight fluted drills are used for sheet metal.

d) centre drills are for long holes, such as gun barrels.

ans. A or D

16. Which of the following is not a typical drill press operation?

a) counter boring.

b) spot facing.

c) counter sinking.

d) none of the above.

ans. D

17. Which of the statements is most correct?

a) reamers are used to finish holes with accuracies not possible when a normal drill is used.

c) taps and reamers can both be used without a machine tool.

d) none of the above.

ans. A

18. What are functions of the following parts of a drill bit. a) body, b) web, c) point, d) tang, e) margin, f) flutes, g) body clearance.

19. What are the purposes of the following drill points. a) conventional, b) flat, c) long angle.

20. What applications are the following drill bits well suited to? a) high helix, b) straight flute, c) gun, d) hard steel, e) core, f) oil hole.

21. What will happen if a drill bit has unequal angles on the cutting edges/lips? What if the edges are not of equal length?

22. Why should most holes be started with a center drill?

23. What are the disadvantages of a thick web found on some drills?

24. What is the purpose of pilot holes?

25. What is the main difference between a) threading operations and tapping operations? b) boring and reaming?

26. List 5 ways work can be held in a lathe.

27. Can peripheral and face milling be done with the same cutter? How common is this?

28. Describe the steps in cutting a 3/8-12-UNC taped hole.

(ans. center drill, drill 1/4”, drill .292”, starting tap, finishing tap)

29. a) Explain the cutting mechanism of a drill bit, and b) suggest the features of a drill bit for cutting a thin piece of sheet metal.

1. A 2” diameter milling cutter with 8 teeth has been selected. What is the table feed if we are milling at 80 ft./min. with a tooth load of 0.004”/tooth?

2. Calculate the machine tool spindle speeds for the following,

a) milling with a 3/4” high speed steel cutter in tool steel work. The CS is 60 ft./min.

b) milling with a 150mm diameter tungsten carbide tipped face cutter in stainless steel work. The CS is 65 m/min.

3. You are given a block of aluminum (5” by 5” by 5”) and you must mill off a 1/16” layer. Using the tables for speeds and feeds, and using the other details provided below, determine a cost for the operation.

• Milling cutter - high speed steel

- diameter 2”

- 10 teeth with a tooth load of 0.004” per tooth

- cost for the machine is \$20.00 per hours

4. Which of the following statements is true for milling?

a) milling cutters can cut with the face and peripheral teeth.

b) the cutting edge moves opposite to the direction used in lathes.

c) indexing is used to cut rounded surfaces.

d) none of the above.

5. What are the advantages of upcut and downcut milling?

6. Which of the following statements is true for milling?

a) milling cutters can cut with the face and not the peripheral teeth.

b) the cutting edge moves opposite to the direction used in lathes.

c) indexing is only used to cut rounded surfaces.

d) none of the above.

ans. D

7. Given a 3” dia. 8 tooth fly cutter, with carbide cutting points, and a steel work piece, recommend, a) RPM, b) feed.

8. Given a 6” dia. high speed steel arbor mill with 10 teeth, that will be cutting cast iron work, recommend, a) RPM, feed.

9. Calculate the indexing required when would be cutting a gear with 36 teeth? Use one of the Brown and Sharp indexing plates.

10. Determine the angular indexing required (on Brown and Sharp, and Cincinatti Standard plates) if we want an angle of 23°30’.

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.

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)

1. An orthogonal cut is made with a carbide tool having a 15° positive rake angle. The various parameters were noted,

- the cut width was 0.25”

- the feed was set at 0.0125”

- the chip thickness was measured to be 0.0375”

- the cutting speed was 250 ft./min.

- the forces measured were Fc = 375 lb. and Ft = 125 lb.

a) Use Merchant’s Circle to scale, and the velocity diagram

b) From the Merchant Circle diagram find the shear angle (φ), friction force (F), friction normal force (N), and shear force (Fs).

c) From the Velocity diagram find the friction velocity (Vf).

d) Calculate values for the coefficient of friction (mu) and the metal removal rate.

e) Calculate values, and compare the results for the results found in a), b) and c).

(ans: F = 218lb., N = 330lb., φ= 19.37°, Fs = 312 lb., μ= 0.948, Vc = 250 ft./min., Vf = 83.5 ft./min. Q = 9.375 in3/min.)

2. The cutting forces for a lathe are listed below,

• work RPM = 125

• feed/rev = 0.005”

• chip thickness = 0.0123”

• rake angle of tool = 14°

• Ft = 150 lb, Fc = 245 lb

• work diameter = 8”

a) Find the horsepower consumed in cutting, shearing and friction.

b) Find a maximum lathe horsepower, assuming the machine efficiency is 95% and it requires 1/8 idle horsepower.

c) Based on the cutting horsepower, what material(s) might we be cutting?

3. What roles do rake and relief angles play in cutting tools?

ans. the rake angle will change the basic cutting parameters. A positive rake (sharp tool) will give lower cutting forces, but less edge strength. A negative or neutral rake will give higher cutting forces, but more strength. The relief angle provide a gap behind the cutting edge so that the tool does not rub the work.

4. Which of these statement is the most correct?

a) a continuous chip with built up edge may result when we try to cut too much metal.

b) a continuous chip will result when cutting very brittle work materials.

c) a discontinuous chip will result when we use fine feeds and speeds.

d) none of the above.

ans. a

5. One of the assumptions behind orthogonal cutting is,

a) that the rake angle is positive.

b) that the tool is only cutting with one edge and one point.

c) the shear plane is a function of before and after chip thicknesses.

d) none of the above.

ans. b

6. Which of these statements is correct?

a) the cutting pressure drops as cutting velocity increases.

b) power required drops as metal temperature and cutting velocity increase.

c) we can use the quantity of metal removed by itself to estimate the required horsepower of a machine tool.

d) all of the above.

ans. a

7. A lathe toolbit with a rake angle of 20° is cutting a section of pipe with an inner diameter of 6” and an outer diameter of 6.25”. The cut has a depth of 0.010” and the chip has a thickness of 0.020”. If the lathe is turning at 200 rpm, and the measured cutting forces are Fc = 300 lb, and Ft = 125lb,

a) what assumption must you make.

b) find the following values using a graphical or numerical solution: (Marks are only awarded for correct answers) Fs, FN, F, N, τ, φ, μ, Vc, Vf, Vs.

c) what is the minimum horsepower required for the machine?

d) given that the tube is aluminum, use another method to find the required horsepower.

8. Calculate the machine tool spindle speeds for the following:

a) Milling with a tungsten carbide tipped face cutter on a stainless steel work piece. C.S. = 65 m/min., cutter dia. = 150mm.

b) Drilling with a High Speed Steel drill in Machine Steel work, with C.S. = 70 ft./min., and a drill diameter of 19/32”

c) Turning on a lathe with a High Speed Steel tool in a mild steel work piece. Surface cutting speed = 100 ft./min., and a workpiece diameter of 2.75”

d) Milling with a High Speed Steel cutter in tool steel work with a cutter speed of 60 ft./min., and a cutter diameter of 3/4”.

a) Why are ceramics normally provided as inserts for tools, and not as entire tools?

b) List the important properties of cutting tool materials and explain why each is important.

10. A turning cut was made in a magnesium workpiece with a feed of 0.050ipr. The cutting speed was 300 fpm, and the cutting force was measured as 200lbs. The lathe is 95% efficient and has an idle horsepower of 0.1HP. Using all of the provided information estimate the horsepower required for the cut.

11. Develop an expression that is the ratio friction power over cutting power using the equations for orthogonal cutting power. Simplify the expression to be in terms of measured values (rake angle, Fc, Ft, and chip thicknesses).

12. A new lathe tool is to be used on cast iron work with a 6” diameter to make a 5” long rough cut in 3 passes. The operation conditions listed below were provided by the supplier or assumed. Calculate the parameters a) to e) as requested.

Cutting Speed = 300 fpm

Feed Rate = 0.008 ipr

Depth of Cut = 0.125”

Idle Horse Power = 0.25

Machine Efficiency = 0.90

a) Spindle RPM

b) Time to make the cut (min.)

c) Metal Removal Rate Q (in.3/min.)

d) Cutting Horse Power (HPc)

e) Minimum Machine Tool Motor HP.

13. Which of these statement is most correct?

a) a continuous chip with built up edge may result when we try to cut brittle metals.

b) a continuous chip will result when cutting very strong work materials.

c) a discontinuous chip will result when we use heavy feeds and speeds.

d) all of the above.

ans. C

14. One of the assumptions behind calculating orthogonal cutting forces is,

a) that the rake angle is positive.

b) that the tool is only cutting with one edge and one point.

c) the shear plane is a function of before and after chip thicknesses.

d) none of the above.

ans. C

15. Which of these statements is most correct?

a) the cutting pressure drops as cutting velocity decreases.

b) power required to cut each cubic inch drops as cutting velocity increases.

c) we can use the quantity of metal removed by itself to estimate the required horsepower of a machine tool.

d) all of the above.

ans. B

16. A new lathe tool is to be used on cast iron work with a 6” diameter to make a 36” long rough cut in 4 passes. The operation conditions listed below were provided by the supplier or assumed. Calculate the parameters a) to e) as requested.

Cutting Speed = 200 fpm

Feed Rate = 0.010 ipr

Depth of Cut = 0.100”

Idle Horse Power = 0.25

Machine Efficiency = 0.90

a) Spindle RPM

b) Time to make the cut (min.)

c) Metal Removal Rate Q (in.3/min.)

d) Cutting Horse Power (HPc)

e) Minimum Machine Tool Motor Horse Power.

ans. a) 127rpm, b) 113min., c) 2.4 ipm, d) 1.23 or 3.94HP, e) 1.62 or 4.63HP

17. a) Define machinability. b) What determines the machinability of a metal?

20. What factors will affect surface finish?

21. Sketch a single edge cutting tool and label the a) face, b) flank, c) nose, d) cutting edge, e) relief, f) shank.

22. Why is the cutting speed important? What will happen at different cutting speeds, from very slow to very fast?

23. We have set up a lathe and are doing an orthogonal cut. The feed rate of the lathe is 0.1mm, and the chip thickness after the cut is 0.2mm. The depth of the chip being cut is 5mm. The surface cutting speed of the tool is 2m/s. The tool has a rake angle of 10deg. The tangential force is measured as 200N, and the cutting force is 500N. a) Calculate the shear force and velocity. b) Calculate the total energy produced in the cut, c) Calculate the energy used to shear d) Explain the difference between the total and the shear energy. [based on Kalpakjian]

24. How is machining different than other processes?

25. What is the difference between a roughing and finishing operation? How does this affect the workpiece and the power consumed?

26. What type of chip is expected at higher cutting speeds?

27. Does the friction power in cutting increase more with a feed or speed increase?

28. Why does cost typically increase for finishing operations.

29. Explain the correction factor ‘c’ used with the HPu values.

(ans. the HPu values are not linear, and ‘c’ corrects for these non-linear values)