1 

DRILLING, REAMING & TAPPING In each of these operations we are producing one or the other kind of hole either blind or through. Drilling Reaming or Tapping isn’t a really tricky operation, but there are certainly some precautions you need to take. The first step in any venture lies in knowing exactly what you need to do. Drilling Reaming or Tapping metal requires the right drill bit, the right measurements and the right amount of patience. Layout-Very first step will be laying out the positions of these holes.

Producing centre marks. The process is called centre punching. Centre punching will produce a small indentation at the given position. The mark will help to start the drill hole at a certain position.

 2 

Drilling,

A drill bit enters the workpiece axially and cuts a blind hole or a through hole with a diameter equal to that of the tool. A drill bit is a multi-point tool and typically has a pointed end. A twist drill is the most commonly used, but other types of drill bits, such as a center drill, spot drill, or tap drill can be used to start a hole that will be completed by another operation.

Secure the piece that you want to drill with a vise or a clamp so it can’t slip. You’ll need both of your hands to keep the drill steady as well, since you’ll be drilling slowly.

Use good-quality drill bits that are clearly labeled "high speed steel" o that are sharp o a golden titanium nitride finish on the bits are better.

Use cutting oil. A pilot hole is a good idea for larger holes. Drill straight down into the metal, at a 90-degree angle when drilling with hand-drill.

o If you drill at an angle, you are more likely to break your drill bit - especially with the smaller sizes.

Use firm downward pressure. o Too little pressure and you will just spin around without cutting.

If the metal or drill-bit starts to discolor, it is overheating - Stop! If it takes too long, it's probably not working - Stop! Ease up on downward pressure when drill is about to go through, when drilling through

holes. When drilling deep holes, you need to bring the drill out of the hole more often to

evacuate chips.

If you are just not making progress, the metal might be too hard. Worse, your continued efforts to drill the metal might be making it harder! (This is called "work-hardening”).

 3 

Feed & Speed for Drilling, It is best to start with a moderate speed and feed, increasing either one, or both, after observing the action and condition of the drill.

Recommended feeds of various diameter drills (HSS) Diameter of Drill - Inches Feed Inches per Revolution Under 1/8 .001 to .003

1/8 to 1/4 .002 to .006

1/4 to 1/2 .004 to .010

1/2 to 1 inch .007 to .015

1 inch and over .015 to .025

RPM Chart for HSS drills

Online Feed & Speed calculator. http://www.custompartnet.com/calculator/drilling-speed-and-feed

Concept of calculation of feed and speed is exactly the same as Lathe machine of Milling machine.

 4 

Drill Geometry,

Drill Kinds,

Straight Shank

Stepdown Shank

Tapered Shank & Sleeves

Note! Extra-long drills are also available in all kinds and designs.

 

Drill Siz

SAE (Sta

N

L

F

Metric dr0.5mm toequivalen

Centre Dsurface. Ofrequentlto wandehole for a

Centre drused cent

es (Diamete

andard Amer

Number sizes

Letter sizes “A

ractional siz

rill sizes are o 25mm. Chnts in inches

Drilling- TraOnce a bit wly provides aer when drilla larger-size

rill bits are cter drills.

er),

rican Equiva

s #80 to #1

A” to “Z”

zes 1/64 to 3

defined by iart on the fo

s of all these

aditional twiwanders off-ca reasonable ing is startedd drill bit or

classified by

alent) drill si

1/32

its diameter ollowing pag

sizes.

st drill bits mcourse it is dstarting poin

d. Center drir to make a c

# sizes. Tab

5 

izes have thr

in decimal nge covers all

may tend to wdifficult to brnt as it is shoill bits are us

conical inden

ble below rel

ree series.

numbers. MoSAE and M

wander whering it back oort and theresed in metalntation in a w

lative dimen

ost commonMetric sizes &

en started onon center. Aefore has a relworking to pworkpiece.

nsions of mo

n sizes starts & shows dec

n an unpreparA center drill

educed tendprovide a sta

st commonly

from imal

red bit

dency arting

y

 6 

Decimal Equivalents of SAE and Metric sizes

English

Metric

Decimal

English

Metric

Decimal

English

Metric

Decimal

English

Metric Decimal

.. .1 .0039 45 2.08 .0820 5 5.22 .2055 7/16 11.11 .4375 .2 .0079 44 2.18 .0860 4 5.31 .2090 29/64 11.51 .4531.. .3 .0118 43 2.26 .0890 3 5.41 .2130 15/32 11.91 .468780 .34 .0135 42 2.37 .0935 7/32 5.56 .2187 .. 12.0 .472479 .37 .0145 3/32 2.38 .0937 2 5.61 .2210 31/64 12.30 .4844

1/64 .40 .0156 41 2.44 .0960 1 5.79 .2280 1/2 12.70 .5000.. . .0157 40 2.50 .0980 A 5.94 .2340 .. 13. .511878 .41 .0160 39 2.53 .0995 15/64 5.95 .2344 33/64 13.10 .515677 .46 .0180 38 2.58 .1015 .. 6.0 .2362 17/32 13.49 .5312. .5 .0197 37 2.64 .1040 B 6.05 .2380 35/64 13.89 .5469

76 .51 .0200 36 2.71 .1065 C 6.15 .2420 .. 14.0 .551275 .53 .0210 7/64 2.78 .1094 D 6.25 .2460 9/16 14.29 .562574 .0225 35 2.79 .1100 1/4 6.35 .2500 37/64 14.68 .5781. . .0236 34 2.82 .1110 F 6.53 .2570 .. 15.0 .5906

73 .61 .0240 33 2.87 .1130 G 6.63 .2610 19/32 15.08 .593772 .64 .0250 32 2.95 .1160 17/64 6.75 .2656 39/64 15.48 .609471 .66 .0260 .. 3.0 .1181 H 6.76 .2660 5/8 15.88 .6250.. .7 .0276 31 3.05 .1200 I 6.91 .2720 .. 16.0 .629970 .71 .0280 1/8 3.18 .1250 .. 7.0 .2756 41/64 16.27 .640669 .74 .0292 30 3.26 .1285 J 7.04 .2770 21/32 16.67 .656268 .79 .0310 29 3.45 .1360 K 7.14 .2810 .. 17.0 .6693

1/32 .79 .0312 28 3.57 .1405 9/32 7.14 .2812 43/64 17.07 .6719.. .8 .0315 9/64 3.57 .1406 L 7.37 .2900 11/16 17.46 .687567 .81 .0320 27 3.66 .1440 M 7.49 .2950 45/64 17.86 .703166 .84 .0330 26 3.73 .1470 19/64 7.54 .2969 .. 18.0 .708765 .89 .0350 25 3.80 .1495 N 7.67 .3020 23/32 18.26 .7187. .9 .0354 24 3.86 .1520 5/16 7.94 .3125 47/64 18.65 .7344

64 .91 .0360 23 3.91 .1540 .. 8.0 .3150 .. 19.0 .748063 .94 .0370 5/32 3.97 .1562 O 8.03 .3160 3/4 19.05 .750062 .97 .0380 22 3.99 .1570 P 8.20 .3230 49/64 19.45 .765661 .99 .0390 .. 4.0 .1575 21/64 8.33 .3281 25/32 19.84 .7812.. 1. .0394 21 4.04 .1590 Q 8.43 .3320 .. 20.0 .787460 1.02 .0400 20 4.09 .1610 R 8.61 .3390 51/64 20.24 .796959 1.04 .0410 19 4.22 .1660 11/32 8.73 .3437 13/16 20.64 .812558 1.07 .0420 18 4.31 .1695 S 8.84 .3480 .. 21.0 .826857 1.09 .0430 11/64 4.37 .1719 .. 9.0 .3543 53/64 21.03 .828156 1.18 .0465 17 4.39 .1730 T 9.09 .3580 27/32 21.43 .8437

3/64 1.19 .0469 16 4.50 .1770 23/64 9.13 .3594 55/64 21.84 .859455 1.32 .0520 15 4.57 .1800 U 9.35 .3680 .. 22.0 .866154 1.40 .0550 14 4.62 .1820 3/8 9.53 .3750 7/8 22.23 .875053 1.51 .0595 13 4.70 .1850 V 9.56 .3770 57/64 22.62 .8906

1/16 1.59 .0625 3/16 4.76 .1875 W 9.80 .3860 .. 23.0 .905552 1.61 .0635 12 4.80 .1890 25/64 9.92 .3906 29/32 23.02 .906251 1.70 .0670 11 4.85 .1910 .. 10.0 .3937 59/64 23.42 .921950 1.78 .0700 10 4.91 .1935 X 10.08 .3970 15/16 23.81 .937549 1.85 .0730 9 4.98 .1960 Y 10.26 .4040 .. 24.0 .944948 1.93 .0760 .. 5.0 .1968 13/32 10.32 .4062 61/64 24.21 .9531

5/64 1.98 .0781 8 5.05 .1990 Z 10.49 .4130 31/32 24.61 .968747 1.99 .0785 7 5.11 .2010 27/64 10.72 .4219 .. 25.0 .9842.. 2. .0787 13/64 5.16 .2031 .. 11.0 .4331 63/64 25.0 .984446 2.06 .0810 6 5.18 .2040 1 25.40 1.000

 

Deburr

When a hhole. Couthe hole atimes it imachine.

Hand deb

Chamfer sharp edgare used have 45 d

ring & Ch

hole is drilleuntersink oand the surfas needed. De.

burring tools

is a small ange and helpsfor chamferidegrees angl

amfering,

d into a worr deburringace into whieburring can

s

ngled surfacs eliminate bing. Chamfele.

,

rk piece, usug tool can rech the hole w

n be dne by a

ce added to aurrs. Chamf

ering tools co

7 

ually a roughmove these was drilled. a hand debur

an edge of a wfer has certaiomes in vari

h edge will aprough edgesSometimes trring-tool or

workpiece. Ain dimensioniety of differ

ppear arounds and put a cthis is a safe

r by counters

A chamfer rn. Usually corent sizes and

d the top of hamfer betw

ety measure sink-tools on

removes the ountersink tod kinds they

the ween other

n the

ools y all

 8 

Countersinking,

Another use of these tools is to make countersink on a hole for fastening countersink type screws. In this case chamfer (which is called countersink here) should be deep enough to seat the screw-head properly, so that head sits below the surface when tightened. Countersinks are available in different angles. Most common ones are 90 and 60 degrees included angle.

 

Counterboring,

A flat-bottomed cylindrical enlargement of the mouth of a hole, usually of slight depth, as for receiving a cylindrical screw head. Counterbores are made with standard dimensions for a certain size of screw. The tip of the counterbore has a reduced diameter section referred to as the pilot, a feature essential to assuring concentricity between the counterbore and the hole being counterbored. Counterbores matched to specific screw sizes generally have integral pilots that fit the clearance hole diameter associated with a particular screw size (e.g., 0.191 inches for a number 10 machine screw).

 9 

 

Guide at the front of a counterboring tool is normaly two fractional sizes bigger than the given screw 

size, for example if we are counterboring for a 1/4 screw the guide diameter will be 9/32 (0.281), so it is 

very imprtant that the drilled hole is right size otherwise the counterboring tool will jam and break. 

 

Tapping,

A tap enters the workpiece axially and cuts internal threads into an existing hole. The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap. The tap is selected based on the major diameter and pitch of the threaded hole. Threads may be cut to a specified depth inside the hole (bottom tap) or the complete depth of a through hole (through tap).

Let us look at the three main component of a thread (1) Major Dia (2) Minor Dia, (3) Pitch

For tapping or internal threads we should drill a hole equal or slightly bigger than minor diameter of a given thread size bofore comencing for tapping. For external or mail threads we will premachine a boss or rod equal or slightle smaller than given thread size and then run a “Threading Die” to machine threads.

To make life easier charts are avilible to find out the right drill size for a given tap. First let us look at thread-pitch series. (What is Right hand & Left hand threads) no no not our topic here.

 10 

National Course threads (UNC or NC)- Coarse threads are those with larger pitch (fewer threads per axial distance like 1/4-20 or 1/2 -13. This is most commonly used series.

National Fine threads (UNF or NF)- Fine threads are those with smaller on finer pitch (more threads per axial distance like 1/4-28 or 1/2 -20

Hand Taps Machine Tap

 

National Pipe threads (NPT)- NPT is US standard for tapered threads used on threaded pipes and fittings. The taper rate for all NPT threads is 1⁄16 (

3⁄4 inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47’. Threaded pipes can provide an effective seal for pipes transporting liquids, gases, steam, and hydraulic fluid. These threads are now used in materials other than steel and brass, including PVC, nylon, bronze and cast iron. The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other.

 11 

Tap identification- If a tap label reads 1/4-20 or M10 x 1.5 what does it mean?

First number 1/4 or M10 always represents major diameter of the thread, second part indicated the pitch, in SAE it is thread per inch and in metric it is distance between two threads. Sometime we see NC or NF mentioned in the label as well. NC or NF are available in Metric taps as well. In NPT threads are identified by fractional size but this size do not relate to any of the dimensions on the actual threads, 1/8 NPT threads will have 0.405 major diameter and 27 threads per inch. NPT threads do not have coarse and fine series.

Tapping Steps,

Identified right size drill for the tap

Machine a hole

Machine a chamfer at the opening of the hole. Chamfer should be slightly bigger than nominal size of the tap i.e. 1/4 or 10mm. Chamfer will help the tap to align and guide.

Run “Tapper” then “Plug” and then “Bottoming” taps, if available. Lot of time on Plug-tap is used.

Make sure tap is perpendicular to the surface, Care is needed specially at the start.

Note! Extreme care is needed when tapping. Taps are extremely hard and brittle and can snap very easily. Use cutting fluid and run tap progressively.

 

Tap Handles

 12 

Tap Drill Chart SAE NC (National Coarse)

Tap size

Screw major dia.

Tap drill size for 75% .dia

clearance drill

#0-80 0.060 3/64 (.0469) 50 (.0700) #1-64 0.073 53 (.0595) 46 (.0810) #2-56 0.086 50 (.0700) 41 (.0960) #3-48 0.099 47 (.0785) 35 (.1100) #4-40 0.112 43 (.0890) 30 (.1285) #5-40 0.125 38 (.1015) 29 (.1360) #6-32 0.138 36 (.1065) 25 (.1495) #8-32 0.164 29 (.1360) 16 (.1770) #10-24 0.190 25 (.1495) 7 (.2010) #12-24 0.216 16 (.1770) 1 (.2280) 1/4-20 .2500 7 (.2010) H (.2660) 5/16-18 .3125 F (.2570) Q (.3320) 3/8-16 .3750 5/16 (.3125) X (.3970) 7/16-14 .4375 U (.3680) 15/32 (.4687) 1/2-13 .5000 27/64 (.4219) 17/32 (.5312) 9/16-12 .5625 31/64 (.4844) 19/32 (.5938) 5/8-11 .6250 17/32 (.5312) 21/32 (.6562) 3/4-10 .7500 21/32 (.6562) 25/32 (.7812) 7/8-9 .8750 49/64 (.7656) 29/32 (.9062) 1"-8 1.000 7/8 (.8750) 1-1/32 (1.0313)1 1/8-7 1.1250 63/64 (.9844) 1-5/32 (1.1562) 

 13 

Tap Drill Chart SAE NF (National Fine) Tap size (major dia. -

threads / inch)

Screw major

dia.

Tap drill size for 75% .dia

Clearance drill

#1-72 0.073 53 (.0595) 46 (.0810) #2-64 0.086 50 (.0700) 41 (.0960) #3-56 0.099 45 (.0820) 35 (.1100) #4-48 0.112 42 (.0935) 30 (.1285) #5-44 0.125 37 (.1040) 29 (.1360) #6-40 0.138 33 (.1130) 25 (.1495) #8-36 0.164 29 (.1360) 16 (.1770) #10-32 0.190 21 (.1590) 7 (.2010) #12-28 0.216 14 (.1820) 1 (.2280) 1/4-28 .2500 3 (.2130) H (.2660) 5/16-24 .3125 I (.2720) Q (.3320) 3/8-24 .3750 Q (.3320) X (.3970) 7/16-20 .4375 25/64 (.3906) 15/32 (.4687) 1/2-20 .5000 29/64 (.4531) 17/32 (.5312) 9/16-18 .5625 33/64 (.5156) 19/32 (.5938) 5/8-18 .6250 37/64 (.5781) 21/32 (.6562) 3/4-16 .7500 11/16 (.6875) 25/32 (.7812) 7/8-14 .8750 13/16 (.8125) 29/32 (.9062) 1"-12 1.000 15/16 (.9375) 1-1/32 (1.0313) 1 1/8-12 1.1250 1-3/64 (1.0469) 1-5/32 (1.1562)

 14 

Tap Drill Chart Metric NC (National Coarse)

Tap size Major dia. mm (inch)

Tap drill mm

Tap drill inch

Clearance mm

Clearance inch

M1.6x0.35 1.6 (.0630) 1.25 #55 1.8 #49 M2x0.4 2.0 (.0787) 1.60 #52 2.4 #41 M2.5x0.45 2.5 (.0984) 2.05 #46 2.9 #32 M3x.05 3.0 (.1181) 2.50 #39 3.4 #29 M3.5x0.6 3.5 (.1378) 2.90 #32 3.9 #23 M4x0.7 4.0 (.1575) 3.30 #30 4.5 #16 M5x0.8 5.0 (.1969) 4.20 #19 5.5 7/32 M6x1 6.0 (.2362) 5.0 #8 6.6 G M8x1 8.0 (.3150) 6.8 J 9.0 T M10x1.5 10.0 (.3937) 8.5 11/32 12.0 31/64 M12x1.75 12.0 (.4724) 10.2 27/64 14.0 35/64 M14x2.0 14.0 (.5512) 12.0 1/2 16.0 5/8 M16x2.0 16.0 (.6299) 14.0 37/64 18.0 45/64 M18x2.5 18.0 (.7087) 15.5 21/32 20.0 51/64 M20x2.5 20.0 (.7874) 17.5 47/64 22.0 7/8 M22x2.5 22.0 (.8661) 19.5 13/16 25.0 1 M24x3 24.0 (.9449) 21.0 7/8 27.0 1-5/64 M27x3 27.0 (1.063) 24.0 1 30.0 1-3/16

 15 

NPT & NPS - Pipe Treads TAP SIZE

TAPER NPT STRAIGHT NPS

DRILL * SIZE

DEC. EQUIV.

Thread OD (MAX)

Normalngageme

nt

DRILL SIZE

DEC. EQUIV.

1/16-27 C .242 .3125 .2611 1/4 .2500 1/8-27 Q .332 .405 .2639 S .34801/4-18 7/16 .438 .540 .4018 29/64 .4531 3/8-18 9/16 .562 .675 .4078 19/32 .5938 1/2-14 45/64 .703 .840 .5337 47/64 .73443/4-14 29/32 .906 1.050 .5457 15/16 .9375 1-11 1/2 1-9/64 1.141 1.315 .6828 1-3/16 1.187 * Drill sizes given permit direct tapping without reaming the hole, but only give a full

ead for the first two or three threads.

Fine pitch – Metric Tap size Major dia.

mm (inch) Tap drill

(mm)

Tap drill

(inch)

Clearance (mm)

Clearance inch (dec.)

M8x1.0 7.0 (0.275) 6.8 H 9.0 T M10x1.0 9.0 (0.354) 8.5 R 12.0 31/64 M12x1.5 10.5 (0.413) 10.2 13/32 14.0 35/64 M14x1.5 12.5 (0.492) 12.0 15/32 16.0 5/8 M16x1.5 14.5 (0.570) 14.0 35/64 18.0 45/64 M18x2.0 16.0 (0.629) 15.5 39/64 20.0 51/64 M20x2.0 18.0 (0.708) 17.5 11/16 22.0 7/8 M22x2.0 20.0 (0.787) 19.5 49/64 25.0 1  

 

Reamin

The geomenough tosurface fiexcellentsometimeoperationdifferencfor the rein) for sothe reameDrilling ftheoretic

A reamerreamer isremoves accurate

Reamers Tapper R

Followinshould be

RPM- Apsize HSS

ng,

metry of a hoo a true cylin

finish for certly in many ces the stringns: a drillingce between themoval of a coft materials er. The drillefollowed by al perfection

r enters the ws a multi-poia minimal adiameter an

are availablReamer and E

ng table givee this much

pproximatelyS drill.

ole drilled innder of a cer

rtain engineecases—usuaency of the r

g to slightly uhe drill diamcertain smaland < 0.13 med hole shoureaming gen

n as possible

workpiece axint tool that hamount of mad a smoothe

le in wide raExpandable

s approximasmaller for a

y reamer sho

n metal by a rtain precise ering applicaally producinrequirementundersize, fo

meter and thel amount of mm (.005 inuld not be ennerally produe.

xially and enhas many fluaterial and isr internal fin

ange of sizes reamer.

ate stock a rea certain size

ould run at h

16 

twist drill mdiameter) an

ations. Althong sufficientls for the hol

ollowed by re reamer diammaterial.) T

n) for hard mnlarged by muces hole ge

nlarges an exutes, which ms often perfonish.

and designs

eamer shoulde reamer.

half or even l

may not be acand may not ough modernly accurate hle's geometryreaming withmeter is call

The allowancmaterials. Larmore than 5%eometry and

xisting hole may be straigormed after d

s such as Han

d remove. In

little bit slow

ccurate enouhave the req

n twist drills holes for moy and finish h a reamer. Ted an allowa

ce should be rger allowan

% of the drillefinish that i

to the diameght or in a hdrilling to ob

nd reamer, M

n other word

wer than the

ugh (close quired smootcan performst applicationecessitate t

The planned ance. (It allo< 0.2 mm (.

nces can damed diameter.s as close to

eter of the tohelix. Reaminbtain both a

Machine ream

ds drilled hol

speed of a s

th m ons—two

ows .008

mage .

ool. A ng more

mer,

le

same

 17 

Trouble Shooting

Symptom Solution Drill produces a very high pitch

squeal

Drill Bit becomes very hot

Drill is running too fast

Drill bit dulls very quickly

Drill bit becomes very hot Lubrication is required

Drill bit Wobbles

Damaged Drill bit

Ensure the Bit is correctly positioned in the chuck

Drill Bit skates across the metal surface

Centre punch is too small

Smaller pilot hole is needed

Drill Bit grabs as it breaks through

Too much Pressure

Drill is running too fast

Drill Press Safety

1. Operate only with the instructor's permission and after you have received proper instruction.

2. Remove jewelry, eliminate loose clothing and confine long hair.

3. Make sure all guards are in place and operating properly.

4. Always use proper eye protection.

5. Hold material securely with a vice or clamps.

6. Be sure the chuck key is removed from the chuck before starting the machine.

7. Select a properly sharpened bit. For metal, center punch when a hole is to be drilled.

8. Turn off the power if the work piece becomes caught in the drill. Do not stop the chuck rotation by hand.

9. Adjust the table or depth stop to avoid drilling into the table. 10. Select the correct speed: Normally, slower for drilling metal, faster for wood. The larger the bit, the slower the speed.