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ALLIED MACHINE & ENGINEERING | RECOMMENDED CUTTING DATA

Tap Drill Information and Formulas | Imperial (inch)

American - Unified Inch Screw Thread

Formulas 1. RPM = (3.82 • SFM) / DIA where: RPM

Probable Mean Oversize

Tap Drill Size

Decimal Equivalent

* Theo % Thread

Probable Hole Size

** Probable % Thread

= revoluƟons per minute (rev/min)

Tap Size 1/2 - 20

SFM

= speed (Ō/min)

29/64

0.4531

72% 72% 83% 87% 70% 65% 79% 72% 87% 75% 65% 72% 84% 77% 72% 72% 77% 75% 76% 65% 84% 67% 72% 72% 82% 77% 67% 87% 72% 67% 87% 72% 76%

0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003

0.4561 0.4754 0.4874 0.5030 0.5148 0.5186 0.5343 0.5499 0.5655 0.5739 0.5811 0.6124 0.6436 0.6526 0.6593 0.6749 0.6905 0.6920 0.7686 0.7843 0.7999 0.8155 0.8624 0.8936 0.8691 0.8780 0.8936 0.9093 0.9249 0.9405 1.0343 1.0499 1.1124

68% 69% 80% 82% 66% 61% 77% 69% 82% 71% 61% 69% 82% 75% 70% 69% 73% 71% 74% 63% 81% 64% 69% 68% 81% 75% 65% 84% 69% 64% 84% 69% 74%

DIA

= diameter of drill (inch)

12.0 mm 0.4724

9/16 - 12

31/64

0.4844 0.5000

2. IPM = RPM • IPR where: IPM = inches per minute (in/min) RPM

1/2

9/16 - 18

13.0 mm 0.5118

31/64 17/32 35/64

0.5156 0.5313 0.5469 0.5625 0.5781 0.6094 0.6406 0.6563 0.6719 0.6875 0.7656 0.7813 0.7969 0.8125 0.8594 0.8906 0.8750 0.8906 0.9063 0.9219 0.9375 1.0313 1.0469 1.1094

= revoluƟons per minute (rev/min)

5/8 - 11 5/8 - 12

IPR

= feed rate (in/rev)

9/16

3. SFM = RPM • 0.262 • DIA where: SFM = speed (Ō/min) RPM

5/8 - 18

14.5 mm 0.5709

37/64

11/16 - 12 39/64

= revoluƟons per minute (rev/min)

41/64

DIA

= diameter of drill (inch)

3/4 - 10

16.5 mm 0.6496

21/32 43/64 11/16 49/64 25/32 51/64 13/16

4. Thrust

= 153,700 • IPR • DIA • K m

3/4 - 12

where: Thrust

3/4 - 16

= axial thrust (lbs) = feed rate (in/rev)

17.5 mm 0.6890

IPR DIA Km

7/8 - 9

= diameter of drill (inch)

= specific cuƫng energy (lbs/in 2 )

7/8 - 14

5. Tool Power = .6991 • IPR • RPM • K m • DIA 2 where: Tool Power = tool power (HP) IPR = feed rate (in/rev) RPM = revoluƟons per minute (rev/min) Km = specific cuƫng energy (lbs/in 2 ) DIA = diameter of drill (inch)

15/16 - 12 55/64 15/16 - 20 57/64

22.0 mm 0.8661

1 - 8

7/8

57/64 29/32 59/64 15/16 1-1/32 1-3/64 1-7/64

1 - 12

1 - 14

1-1/8 - 12

1-1/4 - 7

Material Constants

Taper Pipe Thread (NPT)

Probable Mean Oversize

K m (lbs/in 2 )

Tap Drill Size

Decimal Equivalent

* Theo % Thread

Probable Hole Size

** Probable % Thread

Type of Material

Hardness

Tap Size 1/4 - 18 3/8 - 18 1/2 - 14 3/4 - 14

Plain Carbon and Alloy Steel

85 - 200 BHN 0.79 200 - 275 BHN 0.94 275 - 375 BHN 1.00 375 - 425 BHN 1.15

7/16 9/16

0.4375 0.5625 0.7031 0.9063

- - - -

0.003 0.003 0.003 0.003

0.4405 0.5655 0.7061 0.9093

- - - -

45/64 29/32

High-Temperature Alloys

- -

1.44 0.72

*Based on nominal tap drill diameter. **Based on 0.003" probable mean oversize.

Titanium Alloy Stainless Steels

135 - 275 BHN 0.94 30 - 45 RC 1.08 100 - 200 BHN 0.50 200 - 300 BHN 1.08

To calculate the percent of full thread for a given hole diameter:

Cast Iron

(Basic major diameter of thread - Drill hole size) .0130

Copper Alloy

20 - 80 RB 80 - 100 RB

0.43 0.72 0.22 0.16

% Thread =

# of threads per inch •

Aluminum Alloy Magnesium Alloy

- -

Notes • The above tap drill informaƟon represents probable thread percentages for the standard tap drills stocked at Allied Machine. Special insert diameters may be required in order to meet a user specific percentage of thread requirement. • The 0.003" probable mean oversize hole condiƟon is based on opƟmum cuƫng condiƟons. Probable percent of full thread may vary based on less ideal cuƫng condiƟons. • The table and equaƟons on this page are found in the Machinery’s Handbook . Permission to simplify and print the equaƟons is granted by the editor of the Machinery’s Handbook .

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