Understanding tolerance vs. roughness, what is the unit of roughness

The width between the upper and lower deviations is called the tolerance zone width, and the position of the tolerance zone on the number axis determines the mating properties.

1: When the accuracy requirement is high, there should be a corresponding roughness as a guarantee, however, there is no necessary relationship between accuracy and roughness.

For example, in the example you cited, if the 25 holes are sliding with the shaft, a lower roughness (smoother) is required, and if it is solid.

Decide. With the roughness of the surface, it can be relatively rough.

2: The narrower the tolerance zone, the higher the accuracy.

3: (3) and (4) are both, but their positions on the number axis are different, indicating that the nature of the fit is different (dynamic fit,

Over-fitting, static mating).

Although dimensional tolerance and surface roughness are two concepts, there is a necessary relationship between the two, that is, the higher the accuracy (the smaller the tolerance) the lower the roughness (the smoother the surface). This is formed during processing and is determined by inherent laws. The following questions.

1。The tolerances of (1) and (2) are both, and there is no difference in roughness? A: There is no difference.

3) is smaller than (1) and (2), does it mean that (3) is more accurate? A: Yes, that's right.

3。The tolerances of (3) and (4) are the same, but the decimal places are different, what can be explained? Answer: The hole in description (4) is slightly larger than the hole in (3) "5", and the mating gap is slightly larger "5".

4。If you now have a 25mm diameter shaft that needs to be inserted into the hole, please help you analyze the tolerance of which hole (1) to (4) should be selected under what circumstances? A:

1's, slightly loose; 2, looser; 3 and 4, stricter. (all refer to the fit clearance situation).

5。A hole with a diameter of 25mm has an upper deviation of + and a lower deviation of +

Is there a difference between this and (3)? Is the accuracy higher than (3)? A: There is no essential difference, the tolerance value is the same, and the accuracy is the same. The only difference is that the number of decimal places is not the same.

Hope it helps.

Roughness refers to the surface processing accuracy, smoothness, etc., and tolerance refers to the deviation of the size, and the two are not necessarily related. Therefore, the roughness cannot be judged from the tolerance.

Yes, the tighter the tolerance, the more difficult the machining, and of course the higher the accuracy.

The more decimals (to be precise, the number of significant digits, like significant figures in physics), the higher the accuracy, which is the same as measurement in physics.

Whether it can be inserted into the hole is only related to the diameter of the hole shaft (the diameter of the hole shaft is equal), and has nothing to do with the tolerance, which only reflects the difference in tightness. That is, all four of the above holes are fine.

ps: the fit of the hole shaft has clearance, transition, interference fit (the definition of the three types of fit can be searched, it is very simple, my mobile phone is on the Internet, can not open the big web page), suitable for different situations, should be selected according to the requirements of the project.

There is a mistake upstairs, and of course there is a difference between (5) and (3)!

5) The manufacturing accuracy is the same as (3), but the measurement accuracy of (5) is higher, so the accuracy of (5) is higher overall! There are strict rules for significant figures, and you can't just add zeros to the end, because that means improving the accuracy. For example, the accuracy of the general vernier caliper cannot be written, while the micrometer is.

There is no difference in their roughness.

The key points of the matching selection of the shaft and the hole are: when the temperature of the hole is higher than the temperature of the shaft during movement, the clearance should be reduced; When the temperature of the shaft is higher than the temperature of the hole during movement, the gap should increase; When the bonding length of the mating piece is very long, the gap should be increased; When the geometry accuracy of the part is low, the gap should be increased.

The tolerance of 3) is smaller than that of (1) and (2), indicating that (3) has a higher accuracy.

The tolerances of 3) and (4) are also the same, but the decimal places are different, indicating that the tightness of the fit is different.

There is no direct relationship between surface roughness and tolerance. However, a very rough surface cannot make a small tolerance, and the roughness is generally set according to the use requirements and the tolerance requirements to be achieved. Sometimes there is no tolerance requirement, and a certain roughness requirement is required.

For example, if the electroplated parts do not have a good roughness, there will be no good surface after plating. Again, the tolerance requirement is 6, and it cannot be used without the requirement of roughness or above.

The unit of roughness is: ra.

Ra, a unit of measurement for surface roughness. It is a one-dimensional topography parameter.

Surface geometry features are described using topography parameters. The most commonly used surface topography parameter is surface roughness, which is expressed as the profile curve of a section on a surface. According to the different representation methods, it can be divided into one-dimensional, two-dimensional and three-dimensional topography parameters.

RA is called the contour arithmetic mean deviation or centerline mean. It is the arithmetic mean of the heights of each point on the profile over the measured length.

Measure roughness

1. Comparison method: compare the measured surface with the surface roughness sample marked with a certain evaluation parameter value to judge the roughness of the measured surface.

2. Light cutting method: a measurement method that applies the principle of light cutting to measure surface roughness. An instrument made according to the principle of light section is called a light section microscope.

3. Interferometry: a method for measuring surface roughness by using the principle of light wave interferometry. An instrument made according to the principle of interference is called an interferomicroscope and is generally used to measure surfaces with low roughness values.

Question 1: Is um a unit in the symbol of surface roughness ra? Correct, but it should be noted that ra is usually expressed in m, regardless of whether m is written in the expression. In the same way, ry, rz, etc. are all expressed in this way.

Ra is one of the main parameters of surface roughness assessment, which is defined as: the arithmetic mean of the flat ** above the measured surface profile within a sample length, and the unit of Ra: um (microns).

Question 2: What is the unit of surface roughness ra, rz, and ry m (microns).

Question 3: Is there a unit for surface roughness? The unit of surface roughness is usually um

Surface roughness is usually expressed in RA, RZ, RM (GB T3505-2000, ISO 4287-1997) * Surface roughness refers to the microscopic unevenness with small spacing and small peaks and valleys formed on the machined surface due to different processing methods, machine tool and tool accuracy, vibration and wear and other factors in the machining process, which belongs to geometric error.

Question 4: roughness, what is the unit of m microns, which is 1 1000mm

Question 5: What does the roughness value mean Upstairs is wrong, upstairs is ry value! The unit of roughness is micron, that is, m, is the Ra value, that is to say, the Ra value value refers to the geometric arithmetic average of the actual surface shape to the benchmark in the sampling length, which is very troublesome.

That is, the actual surface is uneven, there will be a central line-like line as the benchmark, the actual surface is divided into two parts, can be divided into prominent peaks and concave valleys, the Ra value is the area of all peaks and valleys divided by the value of the sampling length, and there are many values that indicate the surface roughness, they have no intention of exceptioning R after adding one or a few lowercase letters also indicated, but they are used less, the Ra value is used more, and there is also more Han Z value, It seems to be the average of the values of the ten largest peaks and valleys in the length of the sample. The RA value is roughly the surface roughness that can be obtained by finishing turning. Generally speaking, it is suitable to use the Ra value in the range of Ra value, and the Rz value and Ry value are twice the Ra value, that is.

The roughness is an inverted triangle, and the lower edge of the right-hand side sticks out, and it can't be typed on the keyboard, and the unit is also a grade.

Question 7: What does roughness mean that the arithmetic mean of the absolute value of the profile offset within the sampling length l is.

The concept is too abstract. Simply put, it is the surface roughness obtained by finishing turning, fine planing, fine milling, rough hinging, rough grinding and other processing methods. Basically, the feel is smooth, and there is a slight feeling of processing knife marks. The unit is micron (m).

According to the original old national standard, it is counted as 5. In our case it is pronounced "flower five".

Tolerance surface roughness refers to the unevenness of the machined surface with small spacing and small peaks and valleys.

Basic concept: Surface roughness has a small spacing and a small distance between two peaks or troughs of tiny peaks and valleys (wave distance) is small (less than 1 mm), it belongs to microgeometric error. The smaller the surface roughness, the smoother the surface.

The relationship between the shape tolerance and the surface roughness of the tung tuan:

Although there is no direct relationship between the shape error and the surface roughness in numerical value and measurement, there is also a certain proportional relationship between the two under certain processing conditions, according to the experimental research, in the general accuracy, the surface roughness accounts for 1 5 1 4 of the shape tolerance.

It can be seen that in order to ensure the shape tolerance, the maximum allowable value of the corresponding surface roughness height parameter should be appropriately limited. In general, the tolerance values between dimensional tolerance, shape tolerance, position tolerance, and surface roughness have the following relationship: Dimensional Tolerance, Position Tolerance, Shape Tolerance, Surface Roughness, Height Parameter.

The principle of choosing a tolerance for surface roughness:

1. The roughness value of the friction surface is smaller than that of the non-friction surface.

The higher the friction velocity of the friction surface, the greater the unit pressure subjected to, the higher it should be; The rolling friction surface requires a smaller roughness value than the slippery edge friction surface.

Second, the gap fit, the smaller the gap, the smaller the roughness value should be.

For interference fit, in order to ensure the firm and reliable connection strength, the larger the load, the smaller the roughness value is required. In general, the roughness value of the gap mix is smaller than the interference fit of the coarse silver wheel rock.

3. The roughness of the mating surface should be equivalent to its dimensional accuracy requirements.

When the mating properties are the same, the smaller the size of the part, the smaller the roughness value; At the same accuracy level, the roughness value is smaller than the large size, and the roughness value of the shaft is smaller than the hole (especially the accuracy of IT8 and IT5). The roughness values of the surface subjected to periodic loads and the inner fillet and recess where stress concentration may occur should be small.