drill press text book

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PowerPoint to accompany

Krar • Gill • Smid

Technology of Machine Tools6th Edition

Drilling Machines Section 10

38-2

Drilling Machines

• Probably first mechanical device developed

• Principle of rotating tool to make hole

• One of most common and useful machines in industry

• Come in several types and sizes– From hand-fed to computer-controlled





Drill Presses Unit 38

38-4

Objectives

• Identify six standard operations that may be performed on a drill press

• Identify four types of drill presses and their purposes

• Name and state the purpose of the main parts of an upright and a radial drill

38-5

Drilling Press

• Drilling machine– Spindle

• Turns drill to advance into work (hand or automatically)

– Work table• Holds workpiece rigidly in place as hole drilled

– Used primarily to produce holes in metal– Other operations: tapping, reaming, boring,

counterboring, countersinking, spot-facing

38-6

Standard Operations

• Drilling– Operation of producing hole by

removing metal from solid massusing twist drill


• Countersinking– Operation of producing tapered

or cone-shaped enlargementto end of hole

38-7

Standard Operations

• Reaming– Operation of sizing and producing

smooth, round hole from previouslydrilled or bored hole


• Boring• Truing and enlarging hole by

means of single-point cutting tool

38-8

Standard Operations

• Tapping– Cutting internal threads in hole

with cutting tool called tap


• Counterboring– Enlarging top of previously

drilled hole to given depthto provide square shoulder for head of bolt or capscrew

38-9

Standard Operations

• Spot Facing

• Smoothing and squaring surface around hole to provide seat for head of cap screw or nut– Boring bar fitted with

double-edged cuttingtool

• Pilot section on endto fit into existing hole


38-10

Principal Types of Drilling Machines

• Wide variety of drill presses

• Size of drill press may be designated in different ways by different companies– Some state size as distance from center of

spindle to column of machine– Others state size by diameter of largest circular

piece that can be drilled in center

38-11

Sensitive Drill Press Parts


• Only hand feedmechanism– Control downfeed

pressure

• Manufactured in bench and floor model

• Four main parts– Base, column, table

and drilling head

38-12

Radial Drilling Machine






Drilling Machine Accessories

Unit 39

39-14

Objectives

• Identify and use three types of drill-holding devices

• Identify and use work-holding devices for drilling

• Set up and clamp work properly for drilling

39-15

Versatility of the Drill Press

• Greatly increased by various accessories

• Two categories– Tool-holding devices

• Used to hold or drive cutting tool

– Work-holding devices• Used to clamp or hold workpiece

39-16

Tool-Holding Devices

• Drill press spindle provides means of holding and driving cutting tool

• End may be tapered or threaded for mounting drill chuck

• Most common– Drill chucks– Drill sleeves– Drill sockets

39-17

Drill Chucks

• Most common devices used for holding straight-shank cutting tools

• Most contain three jaws that move simultaneously when outer sleeve turned– Hold straight shank of cutting tool securely

• Two common types– Key – Keyless

39-18

Chucks

• Hold straight-shank drills

• Mounted on drill press spindle– Taper


– Threads

• Held in spindle by self-holdingtaper in larger machines

• Four types of drill chucks

39-19

Types of Drill Chucks• Key-type

– Most common– Three jaws move simultaneously

when outer sleeve turned• Tighten with key

• Keyless – Chuck loosened or tightened by

hand without key

• Precision keyless– Holds smaller drills accurately


39-20

Types of Drill Chucks

• Jacobs impact keyless chuck– Hold small or large drills

accurately using Rubber-Flexcollets

– Gripped or releasedquickly and easily bymeans of built-inimpact device in chuck


39-21

Drill Sleeves and Sockets


• Drill Sleeves– Used to adapt cutting

tool shank to machinespindle if taper on tool issmaller than tapered hole in spindle

• Drill Socket– Used when hole in spindle of drill press to small

for taper shank of drill– Used also as

extension sockets

39-22

Drill Drift

• Used to remove tapered-shank drills or accessories from drill press spindle

• Always place rounded edge up so this edge will bear against round slot in spindle

• Use hammer to tap drill drift and loosen tapered drill shank

• Use board or piece of masonite to protect table

39-23

Work-Holding Devices


• Angle vise– Angular adjustment on base to allow operator to

drill holes at an angle without tilting table

• Drill vise– Used to hold

round, square or odd-shapedrectangular, pieces

– Bolt vise to table for stability

39-24


• Contour vise– Has special movable jaws that automatically

adjust to shape of odd-shaped workpiece• V-blocks

– Made of cast iron or hardened steel– Used in pairs to support round work for drilling

• Step blocks– Used to provide support for outer end of strap

clamps – Various sizes and steps

39-25


• Angle plate– L-shaped piece of cast iron or hardened steel

machined to accurate 90º– May be bolted or clamped to table– Variety of sizes

• Drill jigs– Used in production for drilling holes in large

number of identical parts– Eliminate need for laying out a hole location

39-26


• Clamps or straps– Used to fasten work to drill table or an angle

plate for drilling– Various sizes– Usually supported at

end by step block andbolted to table by T-boltthat fits into table T-slot

• Modifications are double-finger and gooseneck clamps


Finger clamp

U-clamp

Straight clamp

39-27

Clamping Stresses

• Don’t want stresses to cause springing or distortion of workpiece

• Clamping pressures should be applied to work, not step block– Step block should be

slightly higher than work

– Bolt close to work


39-28

Clamping Hints

1. Always place bolt close to workpiece2. Have packing block slightly higher than

work surface being clamped3. Insert piece of paper between machine

table the workpiece to prevent shifting4. Place metal shim between clamp and

workpiece5. Use sub-base or liner under rough casting6. Shim parts that do not lie flat to prevent

rocking





Twist Drills Unit 40

40-30

Objectives

• Identify the parts of a twist drill

• Identify four systems of drill sizes and know where each is used

• Grind the proper angles and clearances on a twist drill

40-31

Twist Drills

• End-cutting tools

• Used to produce holes in most types of materials

• Two helical grooves, or flutes, are cut lengthwise around body of drill– Provide cutting edges and space for cuttings to

escape during drilling process

40-32

Twist Drill Parts

• Most made of high-speed steel– Replaced carbon-steel drills for two reasons

• Can be operated at double the cutting speed

• Cutting edge lasts longer

– Stamped with letters H.S or H.S.S.

• Carbide-tipped drills– Speeds for production have increased up to

300% over high-speed drills

40-33

Three Main Partsof a Drill


Shank

Body

Point

40-34

Shank

• Straight-shank drills– Held in drill chuck– Up to ½ in.

in diameter


• Tapered-shank drills– Fit into internal taper of drill press spindle– Tang provided on end to prevent drill from

slipping

40-35

Body

• Portion of drill between shank and point• Consists of number of parts for cutting• Flutes

– Two or more helical grooves cut around body of drill

– Form cutting edges, admit cutting fluid, allow chips to escape hole

• Body Clearance– Undercut portion of body between margin and

flutes


40-36

Body, cont.

• Margin– Narrow, raised section on body of drill– Next to flutes and extends entire length of flutes– Provides full size to drill body and cutting edges

• Web– Thin partition in center

of drill, extends full length of flutes– Forms chisel edge at cutting end of drill


40-37

Point


40-38

Lip Clearance


• Is the relief ground on point of drill extending from cutting lips back to the heel

40-39

Drill Point Characteristics

1. Control size, quality and straightness of drilled hole

2. Control size, shape and formation of chip

3. Control chip flow up flutes

The use of various point angles and lipclearances, in conjunction with thinningof the drill web, will allow:

40-40

4. Increase strength of drill's cutting edges

5. Reduce rate of wear at cutting edges

6. Reduce amount of drilling pressure required

7. Control amount of burr produced

8. Reduce amount of heat generated

9. Permit use of various speeds and feeds for more efficient drilling

40-41

Conventional Point (118º)

• Most commonly used drill point

• Gives satisfactory results for most general-purpose drilling

• Lip clearance of 8º to 12º for best results– Too much weakens cutting

edge and causes drill to chip– Too little results in use of

heavy drilling pressure


40-42

Long Angle Point (60º to 90º)


• Used on low helix drills for drilling of nonferrous metals, soft cast irons, plastics, fibers, and wood

• Lip clearance generally from 12º to 15º

• Flat may be ground on faceof lips to prevent drillfrom drawing itself intothe soft material

40-43

Flat Angle Point (135º to 150º)

• Used to drill hard and tough materials

• Lip clearance on flat angle point drills only 6º to 8º to provide as much support as possible for cutting edges

• Shorter cutting edge tendsto reduce friction and heat during drilling


40-44

Four Systems of Drill Sizes• Fractional

– Range from 1/64 to 4 in. (steps of 1/64th )

• Number– Range from #1 (.228 in.) to #97 (.0059 in.)

• Letter– Range from A to Z (A = .234 in., Z = .413 in.)

• Millimeter (Metric)– Miniature (0.04 to 0.09 mm, steps of 0.01 mm)

– Straight-shank standard (0.5 to 20 mm)

– Taper-shank (8 up to 80 mm)

40-45

Types of Drills

• Wide variety manufactured to suit specific drilling operations and materials

• Design of drills vary– Number and width of flutes– Amount of helix or rake angle of flutes– Shape of land or margin– Shape of flute: straight or helical– Whether helix is right-hand or left-hand

40-46

Twist Drills• Manufactured from three main materials

– Carbon-steel drills• Used in hobby shops not for machine shop work• Cutting edges wear down quickly

– High-speed steel drills• Used in machine shop work• Cutting edges withstand more heat and wear

– Cemented-carbide drills• Operated at high speeds, withstand higher heat,

and can drill hard materials

40-47

General-Purpose Drill

• Has two Helical flutes• Designed to perform well on wide variety

of materials, equipment and job conditions• Can be made to suit different conditions

and materials by varying point angle, speeds and feeds

• Straight-shank drills called general-purpose jobbers length drills


40-48

Oil Hole Drills

• Have one or two oil holes running from shank to cutting point– Compressed air, oil, or cutting fluid can be

forced through when deep holes being drilled

• Used on turret lathes and screw machines• Cutting fluid cools drill's cutting edges and

flushes chips out of hole


40-49

Step Drills

• Used to drill and countersink or drill and counterbore different sizes of holes in one operation

• May have two or more diameters ground

• Each size or step separated by square or angular shoulder


40-50

Saw-Type Hole Cutter


• Cylindrical-diameter cutter with twist drill in center to provide guide for cutting teeth on hole cutter

• Made in various diameters

• Used for drillingholes in thin materials

• Little burr produced

40-51

Drilling Facts and Problems

• Excessive speed

• Excessive clearance

• Excessive feed

• Insufficient clearance

• Cutting lips with unequal angles

• Cutting lips with unequal in length

• Loading and galling

Examples of eachon following slides

40-52

Excessive speed will cause wear at outer cornersof drill. This permits fewer regrinds of drill dueto amount of stock to be removed in reconditioning.Discoloration is warning sign of excess speed.


40-53

Excessive clearance results in lack of supportbehind cutting edge with quick dulling and poortool life. Despite initial free cutting action. Clearance angle behind cutting lip for generalpurposes is 8º to 12º.


40-54

Excessive feed sets up abnormal end thrust, whichcauses breakdown of chisel point and cutting lips.Failure induced by this cause will be broken or split drill.


40-55

Insufficient clearance causes the drill to rub behindthe cutting edge. It will make the drill work hard,generate heat, and increase end thrust. This resultsin poor holes and drill breakage.


40-56

The web is the tapered central portion of thebody that joins the lands.


40-57

Cutting lips with unequal angles will cause onecutting edge to work harder than the other. Thiscauses torsion strain, bellmouth holes, rapid dulling, and poor tool life.


40-58

Cutting lips unequal in length cause chisel pointto be off center axis and will drill holes oversizeby approximately twice the amount of eccentricity.


40-59

Loading and galling is caused by poor chip

removal with insufficientdissipation of heat so thatmaterial anneals itself to

the cutting edge and flute.This condition frequentlyresults from using wrong

drills for the job or inadequate cutting fluid

application.


40-60

Characteristics of a Properly Ground Drill

• Length of both cutting lips equal

• Angle of both cutting lips be the same

• Lips should be free from nicks or wear

• No sign of wear on margin

Note: Resharpen drill if it does not meet all of these requirements.

40-61

Conditions That Indicate Drill Be Examined and Reground

• Color and shape of chips change• More drilling pressure required• Drill turns blue because of excessive heat• Top of hole out of round• Poor finish produced in hole• Drill chatters when it contacts metal• Drill squeals and may jam in hole• Excessive burr left around drilled hole

40-62

Factors Causing Premature Dulling of Drill

• Drill speed may be too high for hardness of material being cut

• Feed may be too heavy and overload cutting lips

• Feed may be too light and cause lips to scrape rather than cut

• May be hard spots or scale on work surface

40-63

More Factors

• Work or drill may not be supported properly, resulting in springing and chatter

• Drill point may be incorrect for material being drilled

• Finish on lips may be poor

40-64

Procedure to Grind a Drill

1. Wear approved safety glasses

2. Check grinding wheel and dress it to sharpen and/or straighten wheel face

3. Adjust grinder tool rest so it is within .060 in. of wheel face

4. Examine drill point and margins for wear

40-65

5. Hold drill near point with one hand, other hand hold shank of drill slightly lower than point

6. Move drill so it is approximately 59º to face of grinding wheel

7. Hold lip or cutting edge of drill parallel to grinder toolrest

8. Bring lip of drill against grinding wheel and slowly lower drill shank

40-66

9. Remove drill from wheel without moving position of body or hands, rotate drill one-half turn, and grind the other cutting edge

10. Check angle of drill point and length of lips with drill point gage

11. Repeat operations 6-10 until cutting edges are sharp and lands are free from wear nicks






Cutting Speeds and Feeds

Unit 41

41-68

Objectives

• Calculate the revolutions per minute (r/min) for inch and metric size drills

• Select the feed to be used for various operations

• Calculate the revolutions per minute for the reaming operation

41-69

Cutting Speeds and Feeds

• Two important factors– Diameter and material of cutting tool– Type of material being cut

• Speed of twist drill referred to as cutting speed, surface speed or peripheral speed– Distance point on circumference of drill will

travel in 1 min

41-70

Recommended Cutting Speeds

Portion of Table 41.1 from text

Drill Size Cutting Speeds in Feet per Min or Meters per Min in mm 40 ft/min 12 m/min 60 ft/min 18 m/min …1/16 2 2445 1910 3665 28651/8 3 1220 1275 1835 19103/16 4 815 955 1220 1430

Steel Casting Tool Steel

For every job, choose the drill speed that will result in the best production rates!

41-71

Economical Drilling Speed Variables

• Type and hardness of material

• Diameter and material of drill

• Depth of hole

• Type and condition of drill press

• Efficiency of cutting fluid employed

• Accuracy and quality of hole required

• Rigidity of work setup

Most important!

41-72

Revolutions per Minute

• Compute correct number of r/min of drill press spindle for given size drill– Type of material to be drilled– Recommended cutting speed of material– Type of material from which drill is made

41-73

Formula (Inch)

inches)in ncecircumfere (drill

12minute)per feet (min/

D

xCSr

Revolution per minute = number of revolutionsof the drill necessary to attain proper cutting

speed for metal being machined.

where CS = recommended cutting speed in feet per minute for the material being drilled D = diameter of drill being used

41-74

Simplified Formula

• Since not all machines can be set to exact calculated speed, pi (µ) divided into 12 to simplify formula

D

CSr

4 x min/

Example: Calculate r/min required to drill a ½ in hole in cast iron (CS 80) with a high-speed steel drill.

6402/1

320

2/1

4 x 80min/ r

41-75

Feed

• Distance drill advances into work for each revolution

• May be expressed in decimals, fractions of an inch, or millimeters

• Three factors govern rate of feed– Diameter of drill– Material of workpiece– Condition of drilling machine

41-76

Drill Feeds

Table 41.2 Drill feeds

Drill Size Feed per Revolution

in. mm in. mm

1⁄8 and smaller 3 and smaller .001 to .002 0.02 to 0.05

1⁄8 to ¼ 3 to 6 .002 to .004 0.05 to 0.1

¼ to ½ 6 to 13 .004 to .007 0.1 to 0.18

½ to 1 13 to 25 .007 to .015 0.18 to 0.38

1 to 1 ½ 25 to 38 .015 to .025 0.38 to 0.63

General –purpose Work

41-77

Drill Feeds

• General rule: feed rate increases as drill size increases– Too coarse – chip cutting edges– Too light – chattering noise, dulls cutting edge

• Hard steels or alloys use slower feed• Softer metals drilled with faster feed• Blue steel chips indicate too much heat at

cutting edge – Dull cutting edge or too high speed

41-78

Cutting Fluids

• Provide both cooling and lubrication

• Properties of an effective liquid in dissipating heat– Able to absorb heat rapidly– Have good resistance to evaporation– Have high thermal conductivity

Oil: good lubricant, poor coolantWater: best coolant, no lubricating value (promotes rust)





Drilling Holes Unit 42

42-80

Objectives

• Measure the size of inch and metric drills

• Drill the correct size center holes in workpieces

• Drill small and large holes to an accurate location

42-81

Drill Press Safety

1. Do not operate before understanding mechanism and how to stop

2. Always were approved safety glasses

3. Never attempt to hold work by hand

4. Keep your head back from revolving parts

5. As drill begins to break through work, ease up on drill pressure

42-82

6. Always remove burrs from drilled hole with file or deburring tool

7. Never leave chuck key in drill chuck

8. Never attempt to grab work that may have caught in drill

• Stop machine first

9. Always keep floor around drill press clean and free of tools, chips, and oil

42-83

Drilling Hints

1. Treat cutting tools with care

2. Always examine condition of drill point before use – do not use dull tools

3. Make sure drill point angle correct for type of material to be drilled

4. Set correct revolutions per minute for size of drill and workpiece material

42-84

5. Set up work so drill will not cut into machine as it breaks through workpiece

6. Work should always be clamped securely

7. End of workpiece farthest from hole should be placed on left-hand side of table so it will not swing toward operator

8. Always clean tapered drill shank, sleeve, and machine spindle before inserting drill

9. Use shortest drill length possible and/or hold it short in chuck

42-85

10. Good practice to start each hole with center drill

• Provides guide for drill to follow11. Thin workpieces should be clamped to

hardwood block for drilling12. Chips from each flute should be same

shape; if blue during drilling, check drill point condition

13. Drill squeak usually indicates dull drill14. When increased pressure must be applied

during drilling, reason usually dull drill or chip caught in hole between drill and work

42-86

Measuring Size of a Drill

• Good practice to always check drill for size before drilling

• Check for size– Drill gage– Micrometer

• Most accurate

• Check measurement across margin of drill

42-87

Lathe Center Holes

• Use a combination drill and countersink– Commonly called

center drill

• Must be drilled to correct size and depth– Too shallow or deep,

poor support for work


42-88

Spotting Hole Location With a Center Drill

• Chisel end on drill wider than center-punch mark on work– Spot center-punch mark with center drill


Small point on center drill will accurately followcenter-punch mark and provide guide for larger drill

42-89

Spotting Hole Location With a Center Drill

1. Mount small-size center drill in drill chuck2. Mount work in vise

• Do not clamp3. Set drill speed to 1500 r/min4. Bring point of center drill into center-

punch mark and allow work to center itself with drill point

5. Continue drill until one-third of tapered section of center drill has entered work

6. Spot all holes to be drilled

42-90

Spotting Hole


42-91

Drilling Work Held in a Vise

1. Spot hole location with center drill

2. Mount correct-size drill in drill chuck

3. Set drill press to proper speed for size of drill and type of material to be drilled

4. Fasten clamp or stop on left side of table

5. Mount work on parallels in drill vise and tighten it securely

42-92

6. With vise against table stop, locate spotted hole under center of drill

7. Start drill press spindle and begin to drill• Holes up to 12 in. – hold vise against table• Holes over 12 in. – Clamp vise to table

• Drill until full drill point into work• With drill revolving, deep drill point in work and

tighten clamp holding vise

8. Raise drill occasionally and apply cutting fluid during drilling

9. Ease up on drilling pressure as drill starts to break through workpiece

42-93

Drilling to an Accurate Layout

1. Clean and coat surface with layout dye

2. Locate position of hole from two machined edges of workpiece and scribe lines


3. Lightly prick-punch where two lines intersect

4. Check accuracy of punch mark

42-94

5. Scribe circle to indicate diameter of hole


6. Scribe test circle .060 in. smaller than hole

7. Punch four witness marks on circles up to .750 in. in diameter and eight witness marks on larger circles

8. Deepen center of hole location with center punch to provide larger indentation for drill to follow

42-95

9. Center drill work to just beyond depth of drill point

10. Mount proper size drill in machine and drill hole to depth equal to one-half to two-thirds drill diameter

11. Examine drill indentation;should be concentric withinner proof circle


42-96

12. If spotting off center, cut shallow V-grooves with cape or diamond-point chisel on side toward which drill must be moved


13. Start drill in spotted and grooved hole• Drill will be drawn toward direction of

grooves14. Continue cutting grooves

into spotted hole until drillpoint drawn to center

15. Continue to drill hole to desired depth

42-97

Drilling Large Holes

• Drills increase in size; thickness of web also increases to give drill strength– Thicker web, thicker point of drill– Thick web not follow center-punch mark easily

• Two methods to overcome poor cutting action of thick web on large drills– Web is thinned– Lead, or pilot, hole is drilled

42-98

Using Pilot Hole with Large Holes

• Drill pilot hole diameter which is slightly larger than thickness of web

• Care must be taken to drill pilot hole on center

• Pilot hole then followed with larger drill• Problems when pilot hole too large

– Cause chattering– Drill hole out-of-round– Spoil top (mouth) of hole

42-99

Procedure for Drilling Large Holes with Pilot Hole

1. Check print and select proper drill2. Measure thickness of web at point

• Select pilot drill with diameter slightly larger than web thickness

3. Mount workpiece on table4. Adjust height and position of table so drill

chuck can be removed and larger drill placed in spindle after pilot hole drilled and lock table

42-100

5. Place center drill in drill chuck, set proper spindle speed, accurately drill center hole

6. Using proper-size pilot drill, drill pilot hole7. Shut off machine, leaving pilot drill in hole8. Clamp work securely to table9. Raise drill spindle, remove drill and chuck10. Clean taper shank of drill and spindle hole11. Mount large drill in spindle12. Set spindle speed, feed and drill hole to

required depth

42-101

Drilling Round Work in V-Block

1. Select V-block to suit diameter of work2. Mount work in V-block and rotate it until

center-punch mark is in center of work• Check distance from both sides equal

3. Tighten U-clamp securely or hold work in vise

4. Spot hole location with center drill5. Mount proper drill size and set speed6. Dill hole (do not hit V-block or vise when

drill breaks through work)





Reaming Unit 43

43-103

Objectives

• Identify and state the purpose of hand reamers and machine reamers

• Explain the advantages of carbide-tipped reamers

• Calculate the reaming allowance required for each reamer

• Ream a hole by hand in a drill press• Machine ream a hole

43-104

Reamers

• Rotary cutting tool with several straight or helical cutting edges along body

• Used to accurately size and finish hole previously formed by drilling

• Two classifications– Hand– Machine

43-105

Reamer Parts


Three main parts1. Shank2. Body3. Angle of chamfer

43-106

Hand Reamers

• Finishing tools• Holes bored to .003-.005 in.• Square on shank for wrench• Teeth on end tapered so can enter hole easily• Never turn backwards• Taper hand reamers

– Remove frequently toclean


43-107

Machine Reamers

• Used in any machine tool for both roughing and finishing hole

• Called chucking reamers for holding method

• Wide variety of types and styles– Rose reamers– Fluted reamers– Carbide-tipped reamers

43-108

Fluted Reamers

• Have more teeth than rose reamers for comparable diameter

• Lands relieved for entire length• Fluted reamers cut along side as well as at

chamfer on end• Considered finishing tools and used to

bring hole to size


43-109

Carbide-tipped Reamers

• Similar to rose or fluted reamers, except carbide tips been brazed to cutting edges– Resist abrasion and maintain sharp cutting

edges even in high temperatures

• Outlast high-speed steel reamers• Can run at higher speeds and still maintain

their size


43-110

Shell Reamers

• Reamer heads mounted on driving arbor

• Shank of driving arbor may be straight or tapered

• Two slots in end of reamer fit into lugson driving arbor

• Sometimes lockingscrew in arbor


43-111

More Reamers

• Adjustable reamers– Have inserted blades that can be adjusted

approximately at .015 in over or under nominal reamer size

• Adjusting nuts on either end

• Emergency reamers– Drills whose corners have been slightly rounded

and honed if reamer of particular size not available


43-112

Another Reamer

• Expansion reamers– Amount expanded limited– Body slotted and tapered, threaded plug fitted

into end– Turning this plug will allow 1 in. reamer to

expand up to .005 in.


43-113

Reamer Care

1. Never turn reamer backward; ruin edges

2. Always store reamers in separate containers to prevent cutting edges from being nicked

3. Never roll or drop reamers on metal surfaces

4. When not in use, reamer should be oiled

5. Fine, free-cutting grinding wheel should be used for resharpening reamers

43-114

Reaming Allowances

• Amount of material left in hole for reaming operation depends on number of factors– Type of machining operation prior to reaming– Hole punched, rough-drilled, bored

• General rules for amount of material to leave in hole for machine reaming– Holes up to .500 in. diameter, allow .015 in.– Holes over .500 in. diameter, allow .030 in.

43-115

Reaming Speeds

• Factors for determining most efficient speed– Type of material being reamed– Rigidity of setup– Tolerance and finish required in hole

• Generally reaming speed 1/2 to 2/3 speed used for drilling same material

• High speed – used when setup rigid• Lower speed – used when setup less rigid• Coolants improve surface finish and allow speed

43-116

Reaming Feeds

• Feed used for reaming usually two to three times greater than that used for drilling

• Rate varies with material reamed• Generally .001 to .004 in. per flute per rev• Feed too low: glazing, excessive reamer

wear, chatter• Feed too fast: reduce hole accuracy, poor

surface finish• Exception: tapered holes need light feed

43-117

Reaming Hints

1. Examine reamer and remove all burrs from cutting edges with hone

2. Cutting fluid should be used in reaming operation to improve hole finish and prolong life of reamer

3. Helical-fluted reamers should always be used when long holes and those with keyways or oil grooves are reamed

43-118

5. Straight-fluted reamers generally used when extreme accuracy required

6. Use roughing reamer first and then finishing reamer to obtain hole accuracy and good surface finish

7. Never turn reamer backwards8. Never attempt to start reamer on uneven

surface9. Select reamer with incremental cut to

avoid chatter10. Always use stub center in drill press

spindle to keep reamer aligned

43-119

Hand Reaming a Straight Hole


43-120

Procedure for Hand Reaming a Straight Hole

1. Mount work on parallels in vise and clamp it securely to table

2. Drill hole to proper size, leaving allowance for hand reamer to be used

3. Do not move location of work or table; remove drill and mount stub center in drill chuck

4. Start end of reamer in drilled hole

43-121

5. Fasten tap wrench on reamer

6. Engage stub center in center hole on end of reamer

7. With downfeed lever, apply slight pressure while turning reamer clockwise by hand

8. Apply cutting fluid and ream hole

9. When removing reamer, turn it clockwise, never counterclockwise

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Machine Reaming a Straight Hole

1. Mount work on parallels in vise and fasten securely to table

2. Select proper-size drill for reaming allowance required and drill hole

3. Mount proper reamer in drill press

4. Adjust spindle speed to suit reamer and work material

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5. Start drill press and carefully lower spindle until chamfer on reamer starts to cut

6. Apply cutting fluid and feed reamer by applying enough pressure to keep reamer cutting

7. Remove reamer from hole by raising downfeed handle

8. Shut off machine and remove burr from edge of hole





Drill Press Operations

Unit 44

44-125

Objectives

• Counterbore and countersink holes

• Select and use the proper tap to thread a hole in a drill press

• Use three methods to transfer hole locations

44-126

Counterboring

• Operation of enlarging end of hole that has been drilled previously– Depth slightly greater than head of bolt, cap

screw or pin it is to accommodate

• Supplied in variety of styles– Each have pilot in end to keep tool in line with

hole• Some interchangeable pilots to suit variety of holes

44-127

Procedure to Counterbore a Hole

1. Set up and fasten work securely2. Drill proper size of hole in workpiece to suit body

of pin or screw3. Mount correct size of counterbore in drill press4. Set drill press speed to approximately one-quarter

that used for drilling5. Bring counterbore close to work to see that the

pilot turns freely in drilled hole6. Start machine, apply cutting fluid and counterbore

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Countersinking

• Process of enlarging top end of hole to shape of cone to accommodate conical-shaped heads of fasteners– Head will be flush with or below surface

• Countersinks available with various included angles– 60º, 82º, 90º, 100º, 110º, and 120º

44-129

Countersinking

• 82º countersink used to enlarge top of hole so it will accommodate a flat-head machine screw

• Holes to be threadedcountersunk slightly larger than tap diameter

• Speed is approximately1/4th of drilling speed


44-130

Procedure to Countersink a Hole for a Machine Screw

1. Mount an 82º countersink in drill chuck

2. Adjust spindle speed to about ½ that used for drilling

3. Place workpiece on drill table

4. With spindle stopped, lower countersink into hole

• Clamp work if necessary

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5. Raise countersink slightly, start machine, and feed countersink by hand until proper depth is reached.

• Diameter checked by placing inverted screw in countersunk hole

6. If several holes todo, set depth stop

7. Countersink allholes to depthset on gage

44-132

Tapping

• Performed by hand or under power with tapping attachment

• Done immediately after drilling operation

• Hand taps– In sets containing taper, plug, bottoming tap

• Machine taps– Designed to withstand torque required to

thread hole and clear chips

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Set of Hand Taps


Taper

Plug

Bottoming

44-134

Types of Machine Taps


Gun

Stub-flute

Spiral-flute

44-135

Fluteless Tap

• Actually a forming tool used to produce internal threads in ductile material– Copper, brass, aluminum, and leaded steels


Fluteless tap

Lobes of the tap

44-136

Procedure to Tap a Hole by Hand in a Drill Press

1. Mount work on parallels with center-punch mark on work in line with spindle and clamp work securely to drill press table

2. Adjust drill press table height so drill may be removed after hole has been drilled without moving table or work

3. Center drill hole location

44-137

4. Drill hole to correct tap drill size for tap to be used

5. Mount stub center in drill chuck• Or remove drill chuck and mount special

center in drill press spindle

6. Fasten suitable tap wrench on end of tap7. Place tap in drilled hole, lower drill press

spindle until center fits into center hole in tap shank

8. Turn tap wrench clockwise to start tap9. Continue to tap hole, applying light pressure

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Tapping Attachment

• Mounted in a drill press spindle to rotate tap by power– Built-in friction clutch that drives tap clockwise

when drill press spindle fed downward– Reversing mechanism to back tap out of hole

• Two- , three-fluted machine or gun taps used for power – Ability to clear chips

• Tapping speed ranges from 60 – 100 r/min

drill press text book

Documents

drilled hole

types of drill presses

drill pressgreatly

drill pressidentify

hole drilledused

round hole

work hand

drilling head38