Hole Making Operations & Drill Size Chart

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Hole Making Operations & Drill Size Chart

Hole-making is a class of machining operations that are specifically used to cut a hole into a workpiece. Machining, a material removal process, creates features on a part by cutting away the unwanted material and requires a machine, workpiece, fixture, and cutting tool. Hole-making can be performed on a variety of machines, including general machining equipment such as CNC milling machines or CNC turning machines. Specialized equipment also exists for hole-making, such as drill presses or tapping machines. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to a platform inside the machine. The cutting tool is a cylindrical tool with sharp teeth that is secured inside a piece called a collet, which is then attached to the spindle, which rotates the tool at high speeds. By feeding the rotating tool into the workpiece, material is cut away in the form of small chips to create the desired feature.

Hole-making operations are typically performed amongst many other operations in the machining of a part. However, hole-making may be performed as a secondary machining process for an existing part, such as a casting or forging. This can be done to add features that were too costly to form during the primary process or to improve the tolerance or surface finish of existing holes.

Source:https://www.custompartnet.com/wu/hole-making

Machined holes

In machining, a hole is a cylindrical feature that is cut from the workpiece by a rotating cutting tool that enters the workpiece axially. The hole will have the same diameter of the cutting tool and match the geometry (which may include a pointed end). Non-cylindrical features, or pockets, can also be machined, but they require end milling operations not hole-making operations. While all machined holes have the same basic form they can still differ in many ways to best suit a given application. A machined hole can be characterized by several different parameters or features which will determine the hole-making operation and tool that is required.

 

  • Diameter – Holes can be machined in a wide variety of diameters, determined by the selected tool. The cutting tools used for hole-making are available in standard sizes that can be as small as 0.0019 inches and as large as 3 inches. Several standards exist including fractional sizes, letter sizes, number sizes, and metric sizes. A custom tool can be created to machine a non-standard diameter, but it is more cost effective to use the closest standard sized tool.
  • Tolerance – In any machining operation, the precision of a cut can be affected by several factors, including the sharpness of the tool, any vibration of the tool, or the build up of chips of material. The specified tolerance of a hole will determine the method of hole-making used, as some methods are suited for tight-tolerance holes.
  • Depth – A machined hole may extend to a point within the workpiece, known as a blind hole, or it may extend completely through the workpiece, known as a through hole. A blind hole may have a flat bottom, but typically ends in a point due to the pointed end of the tool. When specifying the depth of a hole, one may reference the depth to the point or the depth to the end of the full diameter portion of the hole. The total depth of the hole is limited by the length of the cutting tool.
  • Recessed top – A common feature of machined holes is to recess the top of the hole into the workpiece. This is typically done to accommodate the head of a fastener and allow it to sit flush with the workpiece surface. Two types of recessed holes are a counterbore, which has a cylindrical recess, and a countersink, which has a cone-shaped recess.
  • Threads – Threaded holes are machined to accommodate a threaded fastener and are typically specified by their outer diameter and pitch. The pitch is a measure of the spacing between threads and may be expressed in the English standard, as the number of threads per inch (TPI), or in the metric standard, as the distance in millimeters (mm) between threads.

Hole making operations

Several hole-making operations exist, each using a different type of cutting tool and forming a different type of hole.

 

  • 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
Drilling operation
  • Reaming – A reamer enters the workpiece axially and enlarges an existing hole to the diameter of the tool. A reamer is a multi-point tool that has many flutes, which may be straight or in a helix. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.
Reaming operation
  • 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).
Tapping operation
  • Boring – A boring tool enters the workpiece axially and cuts along the internal surface of an existing hole to enlarge the diameter or obtain more precise dimensions. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head.
Boring operation
  • Counterboring – A counterbore tool enters the workpiece axially and enlarges the top portion of an existing hole to the diameter of the tool. Counterboring is often performed after drilling to provide space for the head of a fastener, such as a bolt, to sit flush with the workpiece surface. The counterboring tool has a pilot on the end to guide it straight into the existing hole.
Counterboring operation
  • Countersinking – A countersink tool enters the workpiece axially and enlarges the top portion of an existing hole to a cone-shaped opening. Countersinking is often performed after drilling to provide space for the head of a fastener, such as a screw, to sit flush with the workpiece surface. Common included angles for a countersink include 60, 82, 90, 100, 118, and 120 degrees.
Countersinking operation

Drill Size Chart

Drill sizeDiameter (in)Diameter (mm)
#1070.00190.0483
0.05 mm0.00200.0500
#1060.00230.0584
#1050.00270.0686
#1040.00310.0787
#1030.00350.0889
#1020.00390.0991
0.1 mm0.00390.1000
#1010.00430.1092
#1000.00470.1194
#990.00510.1295
#980.00550.1397
#970.00590.1499
#960.00630.1600
#950.00670.1702
#940.00710.1803
#930.00750.1905
0.2 mm0.00790.2000
#920.00790.2007
#910.00830.2108
#900.00870.2210
#890.00910.2311
#880.00950.2413
#870.01000.2540
#860.01050.2667
#850.01100.2794
#840.01150.2921
0.3 mm0.01180.3000
#830.01200.3048
#820.01250.3175
#810.01300.3302
#800.01350.3429
#790.01450.3680
1/64 in0.01560.3969
0.4 mm0.01580.4000
#780.01600.4064
#770.01800.4572
0.5 mm0.01970.5000
#760.02000.5080
#750.02100.5334
#740.02250.5715
0.6 mm0.02360.6000
#730.02400.6096
#720.02500.6350
#710.02600.6604
0.7 mm0.02760.7000
#700.02800.7112
#690.02920.7417
#680.03100.7874
1/32 in0.03130.7938
0.8 mm0.03150.8000
#670.03200.8128
#660.03300.8382
#650.03500.8890
0.9 mm0.03540.9000
#640.03600.9144
#630.03700.9398
#620.03800.9652
#610.03900.9906
1 mm0.03941.0000
#600.04001.0160
#590.04101.0414
#580.04201.0668
#570.04301.0922
1.1 mm0.04331.1000
#560.04651.1811
3/64 in0.04691.1906
1.2 mm0.04721.2000
1.3 mm0.05121.3000
#550.05201.3208
#540.05501.3970
1.4 mm0.05511.4000
1.5 mm0.05911.5000
#530.05951.5113
1/16 in0.06251.5875
1.6 mm0.06301.6000
#520.06351.6129
1.7 mm0.06691.7000
#510.06701.7018
#500.07001.7780
1.8 mm0.07091.8000
#490.07301.8542
1.9 mm0.07481.9000
#480.07601.9304
5/64 in0.07811.9844
#470.07851.9939
2 mm0.07872.0000
#460.08102.0574
#450.08202.0828
2.1 mm0.08272.1000
#440.08602.1844
2.2 mm0.08662.2000
#430.08902.2606
2.3 mm0.09062.3000
#420.09352.3749
3/32 in0.09382.3813
2.4 mm0.09452.4000
#410.09602.4384
#400.09802.4892
2.5 mm0.09842.5000
#390.09952.5273
#380.10152.5781
2.6 mm0.10242.6000
#370.10402.6416
2.7 mm0.10632.7000
#360.10652.7051
7/64 in0.10942.7781
#350.11002.7940
2.8 mm0.11022.8000
#340.11102.8194
#330.11302.8702
2.9 mm0.11422.9000
#320.11602.9464
3 mm0.11813.0000
#310.12003.0480
3.1 mm0.12213.1000
1/8 in0.12503.1750
3.2 mm0.12603.2000
#300.12853.2639
3.3 mm0.12993.3000
3.4 mm0.13393.4000
#290.13603.4544
3.5 mm0.13783.5000
#280.14053.5687
9/64 in0.14063.5719
3.6 mm0.14173.6000
#270.14403.6576
3.7 mm0.14573.7000
#260.14703.7338
#250.14953.7973
3.8 mm0.14963.8000
#240.15203.8608
3.9 mm0.15353.9000
#230.15403.9116
5/32 in0.15633.9688
#220.15703.9878
4 mm0.15754.0000
#210.15904.0386
#200.16104.0894
4.1 mm0.16144.1000
4.2 mm0.16544.2000
#190.16604.2164
4.3 mm0.16934.3000
#180.16954.3053
11/64 in0.17194.3656
#170.17304.3942
4.4 mm0.17324.4000
#160.17704.4958
4.5 mm0.17724.5000
#150.18004.5720
4.6 mm0.18114.6000
#140.18204.6228
#130.18504.6990
4.7 mm0.18504.7000
3/16 in0.18754.7625
4.8 mm0.18904.8000
#120.18904.8006
#110.19104.8514
4.9 mm0.19294.9000
#100.19354.9149
#90.19604.9784
5 mm0.19695.0000
#80.19905.0546
5.1 mm0.20085.1000
#70.20105.1054
13/64 in0.20315.1594
#60.20405.1816
5.2 mm0.20475.2000
#50.20555.2197
5.3 mm0.20875.3000
#40.20905.3086
5.4 mm0.21265.4000
#30.21305.4102
5.5 mm0.21655.5000
7/32 in0.21885.5563
5.6 mm0.22055.6000
#20.22105.6134
5.7 mm0.22445.7000
#10.22805.7912
5.8 mm0.22845.8000
5.9 mm0.23235.9000
A0.23405.9436
15/64 in0.23445.9531
6 mm0.23626.0000
B0.23806.0452
6.1 mm0.24026.1000
C0.24206.1468
6.2 mm0.24416.2000
D0.24606.2484
6.3 mm0.24806.3000
1/4 in0.25006.3500
E0.25006.3500
6.4 mm0.25206.4000
6.5 mm0.25596.5000
F0.25706.5278
6.6 mm0.25986.6000
G0.26106.6294
6.7 mm0.26386.7000
17/64 in0.26566.7469
H0.26606.7564
6.8 mm0.26776.8000
6.9 mm0.27176.9000
I0.27206.9088
7 mm0.27567.0000
J0.27707.0358
7.1 mm0.27957.1000
K0.28107.1374
9/32 in0.28137.1438
7.2 mm0.28357.2000
7.3 mm0.28747.3000
L0.29007.3660
7.4 mm0.29137.4000
M0.29507.4930
7.5 mm0.29537.5000
19/64 in0.29697.5406
7.6 mm0.29927.6000
N0.30207.6708
7.7 mm0.30327.7000
7.8 mm0.30717.8000
7.9 mm0.31107.9000
5/16 in0.31257.9375
8 mm0.31508.0000
O0.31608.0264
8.1 mm0.31898.1000
8.2 mm0.32288.2000
P0.32308.2042
8.3 mm0.32688.3000
21/64 in0.32818.3344
8.4 mm0.33078.4000
Q0.33208.4328
8.5 mm0.33478.5000
8.6 mm0.33868.6000
R0.33908.6106
8.7 mm0.34258.7000
11/32 in0.34388.7313
8.8 mm0.34658.8000
S0.34808.8392
8.9 mm0.35048.9000
9 mm0.35439.0000
T0.35809.0932
9.1 mm0.35839.1000
23/64 in0.35949.1281
9.2 mm0.36229.2000
9.3 mm0.36619.3000
U0.36809.3472
9.4 mm0.37019.4000
9.5 mm0.37409.5000
3/8 in0.37509.5250
V0.37709.5758
9.6 mm0.37809.6000
9.7 mm0.38199.7000
9.8 mm0.38589.8000
W0.38609.8044
9.9 mm0.38989.9000
25/64 in0.39069.9219
10 mm0.393710.0000
X0.397010.0838
Y0.404010.2616
13/32 in0.406310.3188
Z0.413010.4902
10.5 mm0.413410.5000
27/64 in0.421910.7156
11 mm0.433111.0000
7/16 in0.437511.1125
11.5 mm0.452811.5000
29/64 in0.453111.5094
15/32 in0.468811.9063
12 mm0.472412.0000
31/64 in0.484412.3031
12.5 mm0.492112.5000
1/2 in0.500012.7000
13 mm0.511813.0000
33/64 in0.515613.0969
17/32 in0.531313.4938
13.5 mm0.531513.5000
35/64 in0.546913.8906
14 mm0.551214.0000
9/16 in0.562514.2875
14.5 mm0.570914.5000
37/64 in0.578114.6844
15 mm0.590615.0000
19/32 in0.593815.0813
39/64 in0.609415.4781
15.5 mm0.610215.5000
5/8 in0.625015.8750
16 mm0.629916.0000
41/64 in0.640616.2719
16.5 mm0.649616.5000
17 mm0.669317.0000
43/64 in0.671917.0656
11/16 in0.687517.4625
17.5 mm0.689017.5000
45/64 in0.703117.8594
18 mm0.708718.0000
23/32 in0.718818.2563
18.5 mm0.728418.5000
47/64 in0.734418.6531
19 mm0.748019.0000
3/4 in0.750019.0500
49/64 in0.765619.4469
19.5 mm0.767719.5000
25/32 in0.781319.8438
20 mm0.787420.0000
51/64 in0.796920.2406
20.5 mm0.807120.5000
13/16 in0.812520.6375
21 mm0.826821.0000
53/64 in0.828121.0344
27/32 in0.843821.4313
21.5 mm0.846521.5000
55/64 in0.859421.8281
22 mm0.866122.0000
7/8 in0.875022.2250
22.5 mm0.885822.5000
57/64 in0.890622.6219
23 mm0.905523.0000
29/32 in0.906323.0188
21/23 in0.913023.1913
59/64 in0.921923.4156
23.5 mm0.925223.5000
15/16 in0.937523.8125
24 mm0.944924.0000
61/64 in0.953124.2094
24.5 mm0.964624.5000
31/32 in0.968824.6063
25 mm0.984325.0000
63/64 in0.984425.0031
1 in1.000025.4000
25.5 mm1.003925.5000
1 1/64 in1.015625.7969
26 mm1.023626.0000
1 1/32 in1.031326.1938
26.5 mm1.043326.5000
1 3/64 in1.046926.5906
1 1/16 in1.062526.9875
27 mm1.063027.0000
1 5/64 in1.078127.3844
27.5 mm1.082727.5000
1 3/32 in1.093827.7813
28 mm1.102428.0000
1 7/64 in1.109428.1781
28.5 mm1.122128.5000
1 1/8 in1.125028.5750
1 9/64 in1.140628.9719
29 mm1.141729.0000
1 5/32 in1.156329.3688
29.5 mm1.161429.5000
1 11/64 in1.171929.7656
30 mm1.181130.0000
1 3/16 in1.187530.1625
30.5 mm1.200830.5000
1 13/64 in1.203130.5594
1 7/32 in1.218830.9563
31 mm1.220531.0000
1 15/64 in1.234431.3531
31.5 mm1.240231.5000
1 1/4 in1.250031.7500
32 mm1.259832.0000
1 17/64 in1.265632.1469
32.5 mm1.279532.5000
1 9/32 in1.281332.5438
1 19/64 in1.296932.9406
33 mm1.299233.0000
1 5/16 in1.312533.3375
33.5 mm1.318933.5000
1 21/64 in1.328133.7344
34 mm1.338634.0000
1 11/32 in1.343834.1313
34.5 mm1.358334.5000
1 23/64 in1.359434.5281
1 3/8 in1.375034.9250
35 mm1.378035.0000
1 25/64 in1.390635.3219
35.5 mm1.397635.5000
1 13/32 in1.406335.7188
36 mm1.417336.0000
1 27/64 in1.421936.1156
36.5 mm1.437036.5000
1 7/16 in1.437536.5125
1 29/64 in1.453136.9094
37 mm1.456737.0000
1 15/32 in1.468837.3063
37.5 mm1.476437.5000
1 31/64 in1.484437.7031
38 mm1.496138.0000
1 1/2 in1.500038.1000

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