ISE 311 Machining I Lab in conjunction with Chapters 21, 22, and 23 in the text book “Fundamentals of Modern Manufacturing” Third Edition Mikell P. Groover

ISE 311Machining I Lab

in conjunction with

Chapters 21, 22, and 23 in the text book“Fundamentals of Modern Manufacturing”

Third EditionMikell P. Groover

April 17th, 2008

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Outline

• Introduction• Basic Principles of Machining• Background Information on Drilling, Turning and

Other operations related to them• Objectives of the Lab• Overview of Lab– Materials and Equipment Used • Demonstration of Machining – Drilling, Facing, and

Turning – Pictures• Summary

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Introduction Basic Principles of Machining

Machining is a manufacturing process in which a cutting tool is used to remove excess material from a workpiece. The material that remains is the desired part geometry. The cutting tool deforms the workpiece in shear and creates scrap called “chips.” As chips fall off the workpiece a new surface is exposed.

A schematic showing a simple machining process

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Almost all solid metals, plastics, and composites can be machined by conventional machining.

Machining can create any regular geometry, i.e., planes, round holes, and cylinders.

Machining can produce dimensions to tolerances of less than 0.001” (0.025mm)

Surface finishes of better than 16μin (0.4 μm) can be produced by machining processes.

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A cutting tool has one cutting edge (facing tool or turning tool) or more than one cutting edges (drill, end mill). The cutting edge separates the chip from the workpiece.

The rake face of a tool guides the chip from the surface of the workpiece and is oriented at an angle α. The rake angle α is measured relative to a plane perpendicular to the work surface.

The flank of a tool provides clearance between the cutting tool and the newly exposed surface to protect the surface from abrasion. The flank is oriented at an angle called the relief angle.

The picture below illustrates the make-up of a cutting tool.

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Machining I Basic Principles of Machining

The three most common types of conventional machining processes are:

– Drilling

– Turning

– Milling

Other conventional machining processes include:– Shaping

– Planing

– Broaching

– Sawing

– Grinding

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Machining I Drilling

Drilling is used to create round holes in workpieces using a rotating tool with two cutting edges. This rotating tool is called a drill or drill bit. This operation is normally performed on a drill press.

Two types of holes can be made: – through holes, in which the drill exits the opposite side of the work

– blind holes , in which the drill does not exit

(a) (b)

Figure depicting (a) through holes and (b) blind holes

The figure below depicts a twist drill – the most

commonly used drill bit.

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Twist drill bit

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The body of a twist drill has two spiral flutes which usually have a 30° helical angle. These flutes act as a passageway for chip extraction from the hole and for coolant to enter the hole (however, cooling is not effective since chips and coolant move in opposite directions).

The thickness of the drill between the flutes, also called the web, provides support over the length of the drill body.

The point of the twist drill is in the shape of a cone and the point angle is typically 118°.

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The twist drill is fed into the workpiece while rotating and the relative motion between the cutting edges of the drill and the workpiece results in material removal and, hence, chip formation.

The flutes provide enough clearance to allow the chips to be extracted. During drilling, however, friction between the chip and cutting surface (rake face) as well as between the outer diameter of the drill and workpiece generates a large amount of heat and, thus, the temperature of the workpiece and drill increases dramatically.

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Drills are limited to a depth of no greater than 4 times its diameter because of the high temperature and the high load on the drilling bit, which:

• Decreases the strength of the drill and makes it easier to break.

• Negatively affects the surface finish of the hole.• Increases the deflection in the drill, which affects the

straightness and dimensional accuracy of the hole


To solve the temperature rise problem, the following is

common: • Peck drilling: the drill is periodically withdrawn from the

hole to clear chips

• Some drills have internal holes in the drill body through which cutting fluid is delivered to the cutting interface.

Increasing flute size makes it easier to clear chips from

the hole but results in smaller web thickness and affects

the drill rigidity (the opposite is also true).

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Prior to drilling, centering (or center drilling) is used to create a starter hole (using a center drill). This is used to:

• Define the location of the hole.

• Solve the “Walking” or “Wandering” problem which happens because of drill deflection before the chisel penetrates the workpiece.

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The following operations are all related to drilling and can be performed once a hole has been created:

– Reaming: a reamer (usually with multiple straight flutes) is used to ream a hole, i.e., slightly enlarge a hole and improve its surface finish and provide tighter tolerances.

– Tapping: a tap is used to create internal screw threads on an existing hole.

– Counterboring generates a stepped hole, i.e., a larger diameter hole is created over a smaller diameter hole. This process is used to seat bolt heads below the surface of a workpiece or flush with the surface.


Operations related to drilling (continued)

– Countersinking is similar to counterboring, but the hole step is conical and is used for flat head screws. Countersinking is used also for deburring.

– Spotfacing is similar to milling. This process is used to provide a flat surface on the workpiece.

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The figure below illustrates the various operations related to drilling.

(a) Reaming(b) Tapping(c) Counterboring(d) Countersinking(e) Center drilling(f) Spot facing

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Machining I The Drill Press

The drill press is the most commonly used machine tool for drilling and the related operations mentioned previously. The most common drill press, and also the one used in the lab procedure, is the upright drill press. The base sits on the floor, has a table for holding the workpiece, a head with a powered spindle for the cutting tool, and a bed and column for support.

Figure showing upright drill press

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Machining I Turning and Facing

Turning is a machining process performed on a lathe in which a single point tool removes material from a rotating cylindrical workpiece. The cutting tool is fed linearly and in a direction parallel to the axis of rotation of the workpiece as shown in the figure below.

*NOTE*In drilling, the cutting tool rotates, while in turning the workpiece rotates.

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The lathe provides the power to rotate the workpiece, feed the tool at the specified rate and cut the workpiece at the necessary depth. Other operations related to turning that can be accomplished by using a lathe include:

– Facing: the tool is fed radially into the rotating workpiece to create a new surface (face) on the end.

– Taper turning: the tool is fed at an angle to the axis of rotation to create a conical geometry.

– Contour turning: The tool follows a contour that is other than straight, thus creating a contoured form in the turned part.

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Other operations related to turning (continued):

– Form turning: a formed cutting tool is fed into the workpiece radially

– Chamfering: the cutting tool cuts an angle on the corner of the cylinder. A very small chamfer can be used to remove burrs usually formed during machining processes and to eliminate sharp corners (for safety reasons).

– Cutoff (or parting): the tool is fed radially (like facing) at some length along the workpiece to cut off the end of the part


Other operations related to turning (continued):

– Threading: a pointed tool is fed linearly across the outside diameter of the workpiece (similar to turning) at a large feed creating external threads on the cylinder

– Boring: a tool is fed linearly and parallel to the axis of rotation to correct a previously drilled hole and/ or to enlarge the diameter of an existing hole in the part

– Drilling: drilling can be performed on a lathe by feeding the drill into the rotating part along its axis.

– Knurling: a knurling tool produces a cross-hatched pattern on the outer diameter of the workpiece

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(a) Facing(b) Taper turning(c) Contour turning(d) Form turning(e) Chamfering(f) Cutoff(g) Threading(h) Boring(i) Drilling(j) Knurling

The figure below displays operations related to turning

(a) (d)(c)(b)

(g)(f)(e)

(h) (i) (j)

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Machining I The Lathe

The engine lathe is a manually operated machine tool which is widely used in low to medium production. Initially, these machine tools were powered by steam engines, hence the term “engine” lathe.

The figure to the left shows the principal components of an engine lathe. The drive unit used to rotate the spindle is enclosed in the headstock. The spindle rotates the workpiece. The tailstock is occasionally used to support one end of the workpiece.

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The cutting tool is held in the tool post. The tool post is mounted on the cross-slide. The cross-slide is mounted on the carriage. The carriage slides along the ways. The ways are built into the bed of the lathe.

The carriage moves in a direction parallel to the axis of rotation and controls the feed rate of the tool. The cross-slide feeds perpendicular to the workpiece. Thus, by moving the carriage, a turning operation can be performed; by moving the cross-slide a facing operation can be carried out.

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The size of a lathe is determined by its swing and maximum distance between centers.

The swing of a lathe is the maximum diameter of the workpiece that can be rotated in the spindle. This diameter is determined as twice the distance from the axis of rotation to the ways of the machine.

The maximum distance between centers is the maximum length of a workpiece that can be mounted between the centers of the headstock and tailstock.

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There are 4 common methods to hold the workpiece in a lathe as shown in the figure below: (a) mounting between centers, (b) chuck, (c) collet, and (d) face plate.

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When mounting the work between the centers, one end of the workpiece is held in place by the headstock and the other end is supported by the tailstock. This method is used for long parts with relatively small diameters.

The chuck (shown to the right) utilizes either three or four jaws to hold the workpiece by its outside diameter. Some jaws are manufactured in a way such that they can hold a tubular workpiece by the inside diameter.

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A collet (shown below) has a tubular bushing with slits over half of its length. These slits allow the collet to be squeezed to reduce its diameter and grasp the cylindrical workpiece. Collets must be made in many various sizes to match the diameter of the workpiece since there is a limit to the amount the diameter of the collet can be reduced.

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A face plate is mounted onto the spindle and is used to hold workpieces with non-cylindrical shapes. The face plate is equipped with custom designed clamps which are manufactured specifically to a particular application.

Machining I Cutting Parameter in turning

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The three cutting parameters in turning are (see the figure

below) :• The cutting speed v (ft/min): the tangential speed

• The depth of cut d (in): the penetration of the cutting tool below the original surface of the work.

• The feed f (in/rev): distance (parallel to the axis of rotation) traveled by the tool per one revolution of the work

Machining IRequired Calculations for this lab

[The following applies for both turning and drilling]

• Look for v and f in tables

• To calculate the spindle RPM (rev/min) from v (ft/min), use the following equation:

• The Material Removal Rate RMR (in3/min) is the volume of material removed (in3) divided by time (min)

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D

vN

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Machining IRequired Calculations for this lab

• Machining power, P, is the energy per unit time required to perform a machining operation (usually in Horse Power, HP)

1 HP = 33, 000 lb*ft/min

• Unit Power Pu or Specific Energy U is the power divided by the Material Removal Rate

• For each material, there is an approximate value of the Unit Power. Look for Pu in tables.

• To calculate P:

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MRU RPP

Machining ITool materials

The most important properties in tool materials are:• Toughness

• Hot Hardness

• Wear resistance

There is always a trade-off between these properties. For example, increasing the hot hardness and wear resistance of the cutting tool generally results in a reduction in toughness.

High Speed steel (HSS) tools are the most common and will be used in this lab.

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Lab Objectives

This lab has the following objectives:

• Become familiar with basic lathe and drill press operations

• Get firsthand experience at trying to maintain tolerances in machining

• Learn to calculate cutting speed, material removal rate, and spindle horsepower

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Lab Safety

• Everyone MUST wear approved safety glasses

• Remove or secure anything which might become caught in rotating machinery. – Remove all jewelry from the hands and wrists. Remove necklaces that

will dangle when stooped over. – Short sleeves are recommended – roll long sleeves up to the elbow. – Loose clothing is not advised. Very baggy shirts, sweaters, sweatshirts,

etc. are not allowed. Unbuttoned shirts or jackets are not allowed. – Secure long hair. When looking down at the ground, if your hair hangs

more than 4” beyond your nose, you need to secure it.

• Do not touch rotating tools or chips clinging to rotating tools.

• Exercise extreme care when touching chips – they are very sharp and can be very hot.

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Lab Procedure – Part A

• You will need to use the drill press and perform drilling operations in order to make the bracket.

• The equipment you will use in this part includes:– Scribe

– Drill press

– Center drill

– 2 drill bits

– Reamer

– Counterbore tool

– Countersink tool

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Head

Forward/Reverse lever

Column

Speed adjustment

Chuck

Spindle

Table

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23/64” Drill 0.375” Reamer

7/32” DrillCenter Drill

Countersink toolCounterbore tool

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Procedure: (refer to the drawing in appendix A)

1. Using the scribe, mark the locations of the holes to be drilled on the workpiece. Make sure to set the correct measurement on the scribe using a scale. Refer to the drawing in appendix A for the correct dimensions.

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Procedure: (refer to drawing in appendix A)

2. Once the center lines for the 3 holes have been marked, clamp the workpiece in the holder on the drill press.

3. Locate the center drill in the chuck and, without turning the drill press on, manually align the center drill to one of the cross hairs that are inscribed on the workpiece

*NOTE*DO NOT attempt to drill the workpiecewith the drill press in the reverse position!

NEVER adjust the speed while themachine is off!

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4. Once the center drill is aligned, return it to its home position. Turn the drill press on by moving the lever to FORWARD and then adjust the speed as stated in appendix A. Apply lubricant as necessary.

5. Hold the workpiece in place with your left hand and with your right hand bring the center drill down to the surface of the workpiece.

6. Slowly create a starter hole. Once a hole has been created return the drill press to its starting position and turn the machine off.

7. Repeat step 3 for the remaining 2 holes. The speed will remain the same. Apply lubricant, if necessary.

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8. Remove the center drill once all three starter holes have been created and replace it with the 23/64” drill.

9. With the drill press off, manually align the drill bit with the middle hole.

10. Turn the machine to FORWARD, adjust the speed accordingly, and apply the lubricant as necessary. Drill a through hole and return the drill press to its home position.

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11. Remove the 23/64” drill bit from the chuck and insert the 3/8” reamer.

12. Turn the machine on, adjust the speed, apply the lubricant and ream the 0.360” hole to 0.375”. Turn off the drill press. Note: If the tool holder was not moved, you do not need to manually align the cutting tool in this step.

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13. Remove the reamer and insert the 7/32” drill into the chuck. Manually align the drill to the center of one of the outside holes.

14. Once aligned, turn on the drill press, adjust the speed, apply the lubricant, and drill a through hole. Once the through hole has been drilled, turn off the machine.

15. Repeat step #15 for the third and final hole.

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16. Remove the 7/32” drill and place the counterbore tool into the chuck.

17. Manually align the counterbore tool with one of the outside holes. Turn on the drill press, adjust the speed, apply the lubricant, and drill a blind hole approximately 3/8” deep.

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18. Turn off the drill press. Remove the counterbore tool and insert the countersink tool into the chuck.

19. Manually align the countersink tool with the third hole. Turn on the drill press, apply the lubricant, and drill a countersink hole.

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20. If time permits, deburr the bottom face of the bracket using the countersink tool. Align the countersink tool with each of the three holes that have been drilled and remove only enough material to remove the burrs created by drilling.

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Lab Procedure – Part B

• You will need to use the engine lathe to perform facing, turning, drilling, and tapping operations in order to make the shaft.

• The equipment you will use in this part includes:– Engine lathe

– Facing tool

– Turning tool

– Center drill

– Drill

– Tap

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ChuckHeadstock

Spindle speed selector

Feed selector

Ways

Lead screw

Bed

Tool post

Cross slide

Tailstock

Feed handwheel

On/Off levers

Cross feedhandwheel

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Turning tool

Facing tool

Tap

Tap guide

Tap holder

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Procedure: (refer to drawing in appendix B)

1. Insert and secure the workpiece into the collet (or chuck).

2. Turn on the lathe by lifting on the lever.

3. Rotate the wheel that controls the feed counterclockwise and place the tool in line with the workpiece.

4. While holding the feed to prevent it from moving, rotate the cross feed in a clockwise direction to face the workpiece. Bring the cross feed back to its starting position after completing the facing operation.

5. Repeat this facing process 1 or 2 more times by slightly feeding the tool to make sure that a flat surface has been generated.

*NOTE*

NEVER power on the lathe if the tool is in contact with the workpiece

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6. Remove the facing tool and insert the turning tool. Adjust the feed stop to 3/8” from the initial position.

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7. Turn on the lathe and cross feed the tool. Once the tool slightly touches the workpiece (chips will be formed and a new surface will be exposed), set and lock the micrometer collar to 0. Next, set the cross feed to 25 (which will remove 0.025” from the diameter) and then feed the tool to the stop.

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8. Bring the feed back to just past the end of the shaft, adjust the cross feed to 50 and repeat the process until approximately 0.110” - 0.115” have been turned.

9. Stop the lathe and measure the diameter using micrometers.

10.Adjust the cross feed to make the final cut and proceed to turn the shaft to its final 0.386” dimension.

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11. Move the cutting tool away from the workpiece. Use the steel file to deburr the edges.

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12. Turn off the lathe. Insert opposite end of workpiece into the chuck.

13. Insert the center drill in the tailstock. Place tailstock near workpiece and lock into position. Turn on lathe and center drill a hole in the shaft.

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14. Return the tail stock to its starting position. Remove the center drill and insert the #25 drill. Power on the lathe and proceed to drill a blind hole approximately 5/8” deep.

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15. Stop the lathe, remove the drill and insert the tap guide into the chuck. Align the #10-32 tap with the hole and the insert the tip of the guide into the rear of the tap. Create a threaded hole by rotating the tap clockwise. For every full turn clockwise, rotate the tap about ½ to ¾ of a turn counterclockwise to remove any chip build-up.

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16. Once a hole has been created, remove the shaft from the collet. Using the arbor press to assemble the shaft into the bracket.

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Summary – Machining 1 Lab

This lab preparation material introduced:

• The basic principles of machining operations with focus on turning, drilling and related operations

• The objectives of and the expected outcomes from the evaluation of experimental trials

• Calculations required for this lab

• The experimental procedure and equipment used

• A number of pictures to familiarize the students with equipment, tools, and procedures related to this lab

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Appendix A – Bracket

Operation Description Tool RPM Oil1 Mark hole locations Scribe and 6”

scaleN/A No

2 Center drill (3) hole Center Drill 900 No

3 Drill thru center hole 23/64” Drill 325 Yes

4 Ream center hole 0.375” Reamer 220 Yes

5 Drill thru (2) outside holes 7/32” Drill 650 Yes

6 Counterbore (1) outside hole

#10 Counterbore 220 Yes

7 Countersink (1) outside hole #10 Countersink 220 Yes

8 Deburr reverse side #10 Countersink 220 No

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Appendix B – Shaft

Operation Description Tool RPM Oil1 Face until perpendicular Facing Tool 900 No

2 Turn 0.376” x 3/8” Turning Tool

900 No

3 Face until perpendicular Facing Tool 900 No

4 Center drill Center Drill 900 No

5 Drill 5/8” deep #25 Drill 900 No

6 Tap #10-32 x 1.2 deep #10-32 Tap N/A Yes

Documents

ISE 311 Machining I Lab in conjunction with Chapters 21, 22, and 23 in the text book “Fundamentals of Modern Manufacturing” Third Edition Mikell P. Groover