CNC Knowledge: Why is the roughness 0.8, 1.6, 3.2, 6.3, 12.5?

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

Do you know why the cylinder bore diameter is 63, 80, 100, 125?

Do you know why the pressure in the cylinders is 6.3, 16, 25, 31.5?

Do you know why the wire specifications are 6, 8, 10, 12, 14, 16?

Do you know where the countless tables in the mechanical design manual and the parameter tables of all product samples come from?

It all comes from the great priority number system.

French engineer Renault saw that the metal cables of hot air balloons had different specifications, so he thought of a way. He raised 10 to the power of five and got a number of 1.6. He then multiplied the numbers to get the next five priority numbers. :

1.0

1.6

2.5

4.0

6.3

This is a geometric sequence, and the last number is 1.6 times the previous number. Then there are only 5 types of steel cables below 10, and there are only 5 types of steel cables from 10 to 100, namely 10, 16, 25, 40, 63.

However, this division method was too sparse, so Mr. Lei continued his efforts and raised 10 to the power of 10, and obtained the R10 priority numbering 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 steel cables within the 10, and there are only 10 types of steel cables between 10 and 100, which is more reasonable. At this point, someone must have said that in this sequence, the first numbers don’t look very different, like 1.0 and 1.25. There is almost no difference, but the gap between 6.3 and 8.0 is large. Is this reasonable?

Reasonable or not, let’s make an analogy. For example, the natural numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 seem very smooth. We use this sequence to pay salaries, giving 1,000 to Zhang San and 2,000 to Li Si. convinced. There is sudden inflation. Give 8,000 to Zhang San and 9,000 to Li Si. In the past, Li Si’s salary was twice that of Zhang San, but now it is 1.12 times. Do you think Li Si would agree? He is the supervisor, and giving him 16,000 is not enough. Zhang San won’t complain that the supervisor has 8,000 more than him.

There are two ways to compare things in nature, namely “relative” and “absolute”! The priority numbering system is relative.

Some people say its product specifications are 10 tons, 20 tons, 30 tons and 40 tons. Now that seems unreasonable, doesn’t it? If you take double, it should be 10 tons, 20 tons, 40 tons, 80 tons, or keep head and tail, it should also be 10 tons, 16 tons, 25 tons, 40 tons, the common ratio is 1.6.

This is “standardization”. I often see people talking about “standardization” on forums. In fact, they talk about “standard parts”. What they do is simply sort out the standard parts of the entire machine. standardization. Actually, it’s not like that. For true standardization, you should serialize all parameters of your product according to the priority number system, and then serialize the functional parameters and dimensions of all components using the priority number system.

The natural numbers are infinite, but in the eyes of mechanical designers, there are only 10 numbers in the world, which are the priority numbers R10. Additionally, when these 10 numbers are multiplied, divided, raised and squared, the result is always among these 10 numbers. How incredible! When you are designing and don’t know which size to choose, just choose from these 10 numbers. How practical!

1.0 N0

1.12N2

1.25N4

1.4N6

1.6 N8

1.8N10

2.0N12

2.24 N14

2.5N16

2.8N18

3.15N20

3.55N22

4.0N24

4.5N26

5.0N28

5.6 N30

6.3 N32

7.1N34

8.0N36

9.0N38

Two priority numbers, such as 4 and 2, have serial numbers N24 and N12, respectively. Multiply them and add their serial numbers. The result is equal to N36, or 8;

Divide and subtract the serial numbers, which equals N12 or 2;

For the cube of 2, multiply its order number N12 by 3 to obtain N36, which is worth 8;

For the square root of 4, divide its order number N24 by 2 to get N12, which is 2. What if we found the fourth power of 2? N12*4=N48, there is no one here, what should I do? In the above list, there is no previous number, which is 10. Its serial number is N40. If the serial number is greater than 40, only look at the part greater than 40. For example, for N48, look at N8, which. is 1.6, then multiply it by 10 to get 16. If the serial number is N88, look at N8 to get 1.6, then multiply it by 100 to get 160, because the serial number of 100 is N80, the serial number of 1000 is N120, and so on.

For mechanical design, these 20 numbers are enough for a lifetime. But sometimes it is necessary to use the R40 numbering system. It is more complete with 40 issues. If that’s not enough, there’s also the R80 series. I know the R40 number system by heart and don’t even need a calculator for general calculations.

In simple terms, calculate the torsional resistance of steel 45 of diameter 40. Its torsion coefficient is 0.5*π*R^3. The torsional stress is half the yield strength of 360, or 180 MPa. and the right hand to pinch the decimal point and mentally calculate the addition and subtraction of serial numbers. Come out in a moment. Did someone say you don’t add a safety factor? Tell me, should I choose 1.25, 1.5 or 2? hehe.

The golden ratio is 0.618, which is 1.618, and there is also 1.6 here. The square root sequence is square root 1, square root 2, square root 3. It’s easy to find, isn’t it? (The serial number of 3 is N19)

What is π squared? equal to 10. Is it practical to calculate that the pressure rod is stable? The twist coefficient of a round rod is approximately 0.1*D^3. Now you can calculate the twist coefficient verbally, right?

Why did the big screw go straight from M36 to M40?

Why is the gear ratio 6.3 or 7.1?

Why does profile steel have a 12.6 gauge rarely seen on the market?

Why did the outsourcing factory call and say there were no 140 square tubes, but there were 120 and 160?

Because the R5 numbering system takes precedence over the R20 numbering system.

Why do standard part parameters have a first sequence and a second sequence? Generally speaking, the first sequence is sequence R5.

Why does Inventor’s screw hole list contain M11.2? Now you know this isn’t a fabricated number, right?

There are also steel plate thickness, steel section model, gear module, all standard parts, functional parameters, dimensional parameters, standard tolerance tables on all product samples industrial, etc. Their origins are slowly becoming clear in our hearts at this time. We can say that we have understood half of the mechanical design manual, as well as industrial products that have not yet been manufactured.

So when we design a product, we can design a series at the same time, instead of doing what is called “standardization” after the design is completed, if the product is intended to be serialized, we can even do it; design a series of products in real working conditions. Designing the product without knowing much about it because the priority numbering system already includes all the models.

The Priority Dial System applications, listed above, can be described as a drop in the ocean, and there are endless applications waiting for us to develop ourselves. Memorize the priority number system. This is a once and for all job.