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 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.
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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" that are sharp o a golden titanium nitride finish on the bits are better. o 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. If you drill at an angle, you are more likely to break your drill bit - especially with o the smaller sizes. Use firm downward pressure. Too little pressure and you will just spin around without cutting. o 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”).
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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. R ec o m m e n d e d f e e d s o f v a r i o u s d i a m e t e r d r i l l s ( H SS) Diameter of Drill - In ches Fe e d I n c h e s p e r Re v o l u t i o n 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.
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Drill Geometry,
Drill Kinds,
Straight Shank
Stepdown Shank
Tapered Shank & Sleeves
Note! Extra-long drills are also available in all kinds and designs. 4
Drill Sizes (Diamet r),
SAE (St ndard American Equiv lent) drill si zes have th ee series.
umber size #80 to #1
Letter sizes “ A” to “Z”
Fractional si es 1/64 to 31/32
Metric d ill sizes are defined by i ts diameter in decimal umbers. M st common sizes starts from 0.5mm t 25mm. Chart on the fo llowing page covers all SAE and M etric sizes shows dec imal equivale ts in inches of all these sizes.
Centre rilling- Tr ditional twist drill bits ay tend to wander whe n started on an unprepa red surface. nce a bit anders off-c ourse it is d ifficult to b ing it back n center. A center drill bit frequentl y provides reasonable starting poi nt as it is sh ort and ther fore has a reduced tend ency to wander when drilling is starte . Center dr ill bits are u sed in metal working to rovide a st rting hole for larger-size d drill bit or to make a c onical inde tation in a orkpiece.
Centre d ill bits are classified by # sizes. Ta le below rel ative dimen sions of mo st commonly used cen er drills.
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Decimal Equivalents of SAE and Metric sizes Englis h
Metri c
Decim al
Englis h
Metri c
Decim al
Englis h
Metri c
Deci mal
Englis h
Metric
Deci mal
..
.1 .2 .3 .34 .37 .40 . .41 .46 .5 .51 .53
.0039 .0079 .0118 .0135 .0145 .0156 .0157 .0160 .0180 .0197 .0200 .0210 .0225 .0236 .0240 .0250 .0260 .0276 .0280 .0292 .0310 .0312 .0315 .0320 .0330 .0350 .0354 .0360 .0370 .0380 .0390 .0394 .0400 .0410 .0420 .0430 .0465 .0469 .0520 .0550 .0595 .0625 .0635 .0670 .0700 .0730 .0760 .0781 .0785 .0787 .0810
45 44 43 42 3/32 41 40 39 38 37 36 7/64 35 34 33 32 .. 31 1/8 30 29 28 9/64 27 26 25 24 23 5/32 22 .. 21 20 19 18 11/64 17 16 15 14 13 3/16 12 11 10 9 .. 8 7 13/64 6
2.08 2.18 2.26 2.37 2.38 2.44 2.50 2.53 2.58 2.64 2.71 2.78 2.79 2.82 2.87 2.95 3.0 3.05 3.18 3.26 3.45 3.57 3.57 3.66 3.73 3.80 3.86 3.91 3.97 3.99 4.0 4.04 4.09 4.22 4.31 4.37 4.39 4.50 4.57 4.62 4.70 4.76 4.80 4.85 4.91 4.98 5.0 5.05 5.11 5.16 5.18
.0820 .0860 .0890 .0935 .0937 .0960 .0980 .0995 .1015 .1040 .1065 .1094 .1100 .1110 .1130 .1160 .1181 .1200 .1250 .1285 .1360 .1405 .1406 .1440 .1470 .1495 .1520 .1540 .1562 .1570 .1575 .1590 .1610 .1660 .1695 .1719 .1730 .1770 .1800 .1820 .1850 .1875 .1890 .1910 .1935 .1960 .1968 .1990 .2010 .2031 .2040
5 4 3 7/32 2 1 A 15/64 .. B C D 1/4 F G 17/64 H I .. J K 9/32 L M 19/64 N 5/16 .. O P 21/64 Q R 11/32 S .. T 23/64 U 3/8 V W 25/64 .. X Y 13/32 Z 27/64 ..
5.22 5.31 5.41 5.56 5.61 5.79 5.94 5.95 6.0 6.05 6.15 6.25 6.35 6.53 6.63 6.75 6.76 6.91 7.0 7.04 7.14 7.14 7.37 7.49 7.54 7.67 7.94 8.0 8.03 8.20 8.33 8.43 8.61 8.73 8.84 9.0 9.09 9.13 9.35 9.53 9.56 9.80 9.92 10.0 10.08 10.26 10.32 10.49 10.72 11.0
.2055 .2090 .2130 .2187 .2210 .2280 .2340 .2344 .2362 .2380 .2420 .2460 .2500 .2570 .2610 .2656 .2660 .2720 .2756 .2770 .2810 .2812 .2900 .2950 .2969 .3020 .3125 .3150 .3160 .3230 .3281 .3320 .3390 .3437 .3480 .3543 .3580 .3594 .3680 .3750 .3770 .3860 .3906 .3937 .3970 .4040 .4062 .4130 .4219 .4331
7/16 29/64 15/32 .. 31/64 1/2 .. 33/64 17/32 35/64 .. 9/16 37/64 .. 19/32 39/64 5/8 .. 41/64 21/32 .. 43/64 11/16 45/64 .. 23/32 47/64 .. 3/4 49/64 25/32 .. 51/64 13/16 .. 53/64 27/32 55/64 .. 7/8 57/64 .. 29/32 59/64 15/16 .. 61/64 31/32 .. 63/64 1
11.11 11.51 11.91 12.0 12.30 12.70 13. 13.10 13.49 13.89 14.0 14.29 14.68 15.0 15.08 15.48 15.88 16.0 16.27 16.67 17.0 17.07 17.46 17.86 18.0 18.26 18.65 19.0 19.05 19.45 19.84 20.0 20.24 20.64 21.0 21.03 21.43 21.84 22.0 22.23 22.62 23.0 23.02 23.42 23.81 24.0 24.21 24.61 25.0 25.0 25.40
.4375 .4531 .4687 .4724 .4844 .5000 .5118 .5156 .5312 .5469 .5512 .5625 .5781 .5906 .5937 .6094 .6250 .6299 .6406 .6562 .6693 .6719 .6875 .7031 .7087 .7187 .7344 .7480 .7500 .7656 .7812 .7874 .7969 .8125 .8268 .8281 .8437 .8594 .8661 .8750 .8906 .9055 .9062 .9219 .9375 .9449 .9531 .9687 .9842 .9844 1.000
.. 80 79 1/64 .. 78 77 . 76 75 74 . 73 72 71 .. 70 69 68 1/32 .. 67 66 65 . 64 63 62 61 .. 60 59 58 57 56 3/64 55 54 53 1/16 52 51 50 49 48 5/64 47 .. 46
. .61 .64 .66 .7 .71 .74 .79 .79 .8 .81 .84 .89 .9 .91 .94 .97 .99 1. 1.02 1.04 1.07 1.09 1.18 1.19 1.32 1.40 1.51 1.59 1.61 1.70 1.78 1.85 1.93 1.98 1.99 2. 2.06
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Debur ing & Chamfering, When a ole is drille d into a wor k piece, usually a rough edge will a ppear aroun d the top of the hole. Co ntersink or deburrin tool can remove these rough edge and put a c hamfer bet een the hole and the surf ce into whi ch the hole as drilled. Sometimes this is a safe ty measure other times it is needed. D burring can be dne by hand debu ring-tool or by counters ink-tools on the machine. Hand de urring tool
Chamfer is a small angled surfac e added to an edge of a workpiece. A chamfer r emoves the sharp ed e and helps eliminate burrs. Chamf er has certai n dimensio . Usually c untersink t ols are used for chamfering. Chamfering tools c mes in vari ety of differ ent sizes an d kinds they all have 45 egrees angl e.
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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).
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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.
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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 1 3 and fittings. The taper rate for all NPT threads is ⁄ 16 ( ⁄ 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.
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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 Plugtap 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
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Tap Drill Chart SAE NC (National Coarse) Tap size
#0-80 #1-64 #2-56 #3-48 #4-40 #5-40 #6-32 #8-32 #10-24 #12-24 1/4-20 5/16-18 3/8-16 7/16-14 1/2-13 9/16-12 5/8-11 3/4-10 7/8-9 1"-8 1 1/8-7
Screw major dia.
0.060 0.073 0.086 0.099 0.112 0.125 0.138 0.164 0.190 0.216 .2500 .3125 .3750 .4375 .5000 .5625 .6250 .7500 .8750 1.000 1.1250
Tap drill size for 75% .dia
clearance drill
3/64 (.0469) 53 (.0595) 50 (.0700) 47 (.0785) 43 (.0890) 38 (.1015) 36 (.1065) 29 (.1360) 25 (.1495) 16 (.1770) 7 (.2010) F (.2570) 5/16 (.3125) U (.3680) 27/64 (.4219) 31/64 (.4844) 17/32 (.5312) 21/32 (.6562) 49/64 (.7656) 7/8 (.8750) 63/64 (.9844)
50 (.0700) 46 (.0810) 41 (.0960) 35 (.1100) 30 (.1285) 29 (.1360) 25 (.1495) 16 (.1770) 7 (.2010) 1 (.2280) H (.2660) Q (.3320) X (.3970) 15/32 (.4687) 17/32 (.5312) 19/32 (.5938) 21/32 (.6562) 25/32 (.7812) 29/32 (.9062) 1-1/32 (1.0313) 1-5/32 (1.1562)
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Tap Drill Chart SAE NF (National Fine) Tap size (major dia. threads / inch)
#1-72 #2-64 #3-56 #4-48 #5-44 #6-40 #8-36 #10-32 #12-28 1/4-28 5/16-24 3/8-24 7/16-20 1/2-20 9/16-18 5/8-18 3/4-16 7/8-14 1"-12 1 1/8-12
Screw major dia. 0.073 0.086 0.099 0.112 0.125 0.138 0.164 0.190 0.216 .2500 .3125 .3750 .4375 .5000 .5625 .6250 .7500 .8750 1.000 1.1250
Tap drill size for 75% .dia
Clearance drill
53 (.0595) 50 (.0700) 45 (.0820) 42 (.0935) 37 (.1040) 33 (.1130) 29 (.1360) 21 (.1590) 14 (.1820) 3 (.2130) I (.2720) Q (.3320) 25/64 (.3906) 29/64 (.4531) 33/64 (.5156) 37/64 (.5781) 11/16 (.6875) 13/16 (.8125) 15/16 (.9375) 1-3/64 (1.0469)
46 (.0810) 41 (.0960) 35 (.1100) 30 (.1285) 29 (.1360) 25 (.1495) 16 (.1770) 7 (.2010) 1 (.2280) H (.2660) Q (.3320) X (.3970) 15/32 (.4687) 17/32 (.5312) 19/32 (.5938) 21/32 (.6562) 25/32 (.7812) 29/32 (.9062) 1-1/32 (1.0313) 1-5/32 (1.1562)
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Tap Drill Chart Metric NC (National Coarse) Tap size
Major dia. mm (inch)
Tap drill mm
Tap drill inch
M1.6x0.35 M2x0.4 M2.5x0.45 M3x.05 M3.5x0.6 M4x0.7 M5x0.8 M6x1 M8x1 M10x1.5 M12x1.75 M14x2.0 M16x2.0 M18x2.5 M20x2.5 M22x2.5 M24x3 M27x3
1.6 (.0630) 2.0 (.0787) 2.5 (.0984) 3.0 (.1181) 3.5 (.1378) 4.0 (.1575) 5.0 (.1969) 6.0 (.2362) 8.0 (.3150) 10.0 (.3937) 12.0 (.4724) 14.0 (.5512) 16.0 (.6299) 18.0 (.7087) 20.0 (.7874) 22.0 (.8661) 24.0 (.9449) 27.0 (1.063)
1.25 1.60 2.05 2.50 2.90 3.30 4.20 5.0 6.8 8.5 10.2 12.0 14.0 15.5 17.5 19.5 21.0 24.0
#55 #52 #46 #39 #32 #30 #19 #8 J 11/32 27/64 1/2 37/64 21/32 47/64 13/16 7/8 1
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Cleara Cleara nce nce mm inch
1.8 2.4 2.9 3.4 3.9 4.5 5.5 6.6 9.0 12.0 14.0 16.0 18.0 20.0 22.0 25.0 27.0 30.0
#49 #41 #32 #29 #23 #16 7/32 G T 31/64 35/64 5/8 45/64 51/64 7/8 1 1-5/64 1-3/16
NPT & NPS - Pipe Treads TAP SIZE
TAPER NPT DRILL * DEC. SIZE QUIV.
1/16-27 1/8-27 1/4-18 3/8-18 1/2-14 3/4-14 1-11 1/2
C Q 7/16 9/16 45/64 29/32 1-9/64
.242 .332 .438 .562 .703 .906 1.141
Threa d OD MAX) .3125 .405 .540 .675 .840 1.050 1.315
STRAIGHT NPS Normal gageme nt .2611 .2639 .4018 .4078 .5337 .5457 .6828
DRILL SIZE
DEC. QUIV.
1/4 S 29/64 19/32 47/64 15/16 1-3/16
.2500 .3480 .4531 .5938 .7344 .9375 1.187
* Drill sizes given permit direct tapping without reaming the hole, but only give a full ad for the first two or three threads.
Fine pitch – Metric Tap size
M8x1.0 M10x1.0 M12x1.5 M14x1.5 M16x1.5 M18x2.0 M20x2.0 M22x2.0
Major dia. mm (inch) 7.0 (0.275) 9.0 (0.354) 10.5 (0.413) 12.5 (0.492) 14.5 (0.570) 16.0 (0.629) 18.0 (0.708) 20.0 (0.787)
Tap drill (mm) 6.8 8.5 10.2 12.0 14.0 15.5 17.5 19.5
Tap drill (inch) H R 13/32 15/32 35/64 39/64 11/16 49/64
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Clearance Clearance inch (mm) (dec.) 9.0 12.0 14.0 16.0 18.0 20.0 22.0 25.0
T 31/64 35/64 5/8 45/64 51/64 7/8 1
Reami g, The geo etry of a h le drilled in metal by a twist drill m ay not be a curate enou gh (close enough to a true cyli nder of a ce tain precise diameter) a nd may not have the req uired smoot h surface f inish for cer tain enginee ring applica tions. Altho ugh modern twist drills can perfor excellent ly in many ases—usua lly producin g sufficientl y accurate oles for mo st applicati ns— sometim s the stringency of the equirement s for the hol e's geometr and finish necessitate t wo operatio s: a drilling to slightly ndersize, f llowed by r eaming wit a reamer. he planned differenc e between t e drill dia eter and the reamer dia meter is call ed an allow nce. (It all ws for the r moval of a ertain small amount of material.) T he allowanc e should be < 0.2 mm (.008 in) for s ft materials and < 0.13 m (.005 in) for hard m aterials. Lar ger allowances can dam age the ream r. The drill d hole shou ld not be enlarged by m ore than 5 of the drilled diameter. Drilling ollowed by reaming ge erally prod uces hole g ometry and finish that i s as close to theoretical perfectio as possible . A reame enters the orkpiece a ially and e reamer i a multi-point tool that as many fl removes a minimal amount of material and i accurate diameter and a smoother internal fi
larges an e isting hole to the diam ter of the to ol. A tes, which ay be strai ght or in a helix. Reami g often perf rmed after rilling to o tain both a more ish.
Reamers are availabl e in wide range of sizes and design such as Ha nd reamer, Tapper eamer and xpandable reamer.
achine rea mer,
Followin g table give s approximate stock a r amer shoul remove. In other word s drilled hol e should b this much smaller for certain siz reamer.
RPM- A proximatel y reamer sh uld run at half or even little bit slo er than the speed of a s ame size HSS drill.
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Trouble Shooting
Symptom Drill produces a very high pitch squeal
Solution Drill is running too fast
Drill Bit becomes very hot Drill bit dulls very quickly Lubrication is required Drill bit becomes very hot Damaged Drill bit Drill bit Wobbles
Drill Bit skates across the metal surface Drill Bit grabs as it breaks through
Ensure the Bit is correctly positioned in the chuck Centre punch is too small Smaller pilot hole is needed 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.
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