Automatic Determination of Roughness

During the second development and the design of AutoCAD, it’s necessary for us to choose roughness according to the part’s precision grade, it’s connecting relationship, and look up the list. In order to make the designer and programmer get the precision grade quickly and accurately, and decide the roughness in the drawing, this article analyze the relationship between the precision and roughness on the basis of analyzing method, and consider the experience in practice, then carry out a set of method formula, so that design and programming Autolisp become easier. Firstly,Research and analysis of the relationship between roughness and part’s precision. 1) Define the lowest value of roughness according to the tolerance of dimensions In general, roughness and dimension tolerance are advanced when the fit is decided, their function is different, and there is no fixed math relationship, but we should coordinate them. They always coordinate with the fitness. As a result, we can get the lowest value of roughness though dimension tolerance. 2) The conversion relationship between Ra and Rz In general, Ra and Rz can be decided freely. The result is different if there are two kinds of parameter, we always consider Ra when the grade is 5～12, but Rz is considered when the grade is 1～4. When a grade of roughness is needed, it’s value must not be lower than this grade, but can tigher than it. The roughness is devided in 12 grade in ISO1320, that is Ra:N1～N12. According to the reference document, we know the conversion relationship between Ra and Rz. 3) The relationship between Rz and dimension tolerance The relationship between Rz and dimension tolerance is decided as blow: it’s value is 1/3～1/7 of Rz. Large dimension needs large tolerance, and get the Rz by small ratio. Small dimension needs small tolerance, and get the Rz by large ratio, but not higher than 1/2. Secondly,The relationship formula between Ra and dimension tolerance. Devide it into sections according to the priority sequence of number, then calculate tolerance unit i by getting the average of the start dimension and end dimension (D 1D 2 ), which make the error consistent and the error is easy to arrange in the form of priority sequence of number. The relationship formula between tolerance and roughness is below: R a=14R z=14IT·N13～17=112～128·N·0.45KF(S 3D+0.001D](roughness grade≤5). R a=15R z=15IT·N13～17=115～135·N·(roughness grade≤5). R a=15R z=15IT·N13～17=115～135·N·3D+0.001D](roughness grade≥6). (roughness grade≥6).

During the second development and the design of AutoCAD, it s necessary for us to choose roughness according to the part s precision grade, it s connecting relationship, and look up the list. In order to make the designer and programmer get the precision grade quickly and accurately, and decide the roughness in the drawing, this article analyze the relationship between the precision and roughness on the basis of analyzing method, and consider the experience in practice, then carry out a set of method formul...