Technical Information for Thread Milling Technical Information for Thread Milling Tool Selection For indexable and solid carbide Mill Threads The following chart provides a fairly accurate visual selection tool for Internal Threading. The chart is suitable for the following thread forms : ISO, UN, WHIT, NPT, NPTF, BSPT and PG . Conversion of Cutting Speed to P=Thread Pitch A Rotational Speed TPI mm D= Tool cutting diameter 1 4 6.0 Conversion of selected cutting speed to rotational N speed is calculated by the following formula: 5 5.0 Example: v=120 m/min D=30 mm 6 4.0 N= Vx 1000 JT x D 120 x 1000 3.14 x 30 =1274 RPM V V D D=Cutting diameter 8 3.5 3.0 m 00 D=21 D=29 10 2.5 1 10 O Q o 12 2.0 0 " 8 16 1.5 Internal Thread External Thread u 20 1.25 24 1.0 D=9 D=12 32 0.75 3 48 0.5 090 Left Hand Right Hand Left Hand Thread Thread Thread mm 4 5 6 7 8 9 10 11 12 13 14 15 16 18 20 22 24 26 28 30 32 34 36 38 40 44 48 52 58 64 § ¥ inch 1/4 3/8 1/2 5/8 3/ 4 1 1.25 1.5 2 2.5 * 8