Why are CNC parts thread specifications 6, 8, 10, 12, 14, 16?

Do you know why the roughness is 0.8, 1.6, 3.2, 6.3, 12.5?

Do you know why are CNC parts thread specifications are 6, 8, 10, 12, 14, 16?

Everything comes from the great priority number system.

French engineer Renault saw a variety of specifications of the wire rope on the hot air balloon, he thought of a way, 10 to the power of 5, get a number 1.6, and then turn and multiply, get 5 priority number as follows :1.0, 1.6, 2.5, 4.0, 6.3.

This is a geometric sequence, the last number is 1.6 times of the first number, then there are only 5 types of steel wire ropes below 10, and there are only 5 types of steel wire ropes from 10 to 100, namely 10, 16, 25, 40, 63. But this division method is too sparse, so Mr. Lei made persistent efforts to raise 10 to the power of 10, and obtained the R10 priority number system as follows: 1.0, 1.25, 1.6, 2.0, 2.5, 3.15, 4.0, 5.0, 6.3, 8.0.

The common ratio is 1.25, so there are only 10 types of wire ropes within 10, and only 10 types of wire ropes from 10 to 100, which is more reasonable.

Natural numbers are infinite, but in the eyes of mechanical designers, there are only 10 numbers in the world, and it is the priority number R10. Moreover, these 10 numbers are multiplied, divided, squared, and square rooted, and the result is still in these 10 numbers. When you design, when you don’t know what size to choose, it’s in these 10 numbers select.

1.0 N0、1.12 N2、1.25 N4、1.4 N6、1.6 N8、1.8 N10、2.0 N12、2.24 N14、2.5 N16、2.8 N18、3.15 N20、3.55 N22、4.0 N24、4.5 N26、5.0 N28、5.6 N30、6.3 N32、7.1 N34、8.0 N36、9.0 N38

Two priority numbers, such as 4 and 2, whose serial numbers are N24 and N12 respectively, multiply them, add their serial numbers, and the result is equal to N36, that is, 8;

Divide and subtract the serial number, which is equal to N12, which is 2;  for the cube of 2, multiply its serial number N12 by 3 to get N36, which is 8;

For mechanical design, these 20 numbers are enough. But sometimes you need to use the R40 series, and if you have 40 numbers, it's better, or if you don't have enough, you can use the R80 series.

Simply calculate the torsion resistance of 40 diameter steel 45, its torsion coefficient is 0.5*π*R^3, the torsional stress selected half of the yield point 360, namely 180MPa, PI 3.15.