Experience with scale settings in AUTOCAD

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Experience with scale settings in AUTOCAD 1. Drawing scale: We commonly refer to AutoCAD as being used for 1:1 drawing, and this 1:1 ratio is considered a scale concept; however, in reality, AutoCAD does not have such a thing as 1:n drawing. Let’s not assume for now that entering 100 means 100 mm; strictly speaking, what we enter is 100 graphic units, as we use the metric system, and in this system, 1 graphic unit equals 1 mm in AutoCAD. Drawing involves creating a representation based on the specified drawing units, by accurately reflecting the actual dimensions of the object. For a line that is 1 meter long, you enter 1000; you don’t enter 1000/100=10 just because the drawing scale is 1:100. In this way, in AutoCAD drawing, the concept of a drawing scale actually does not exist. 2. Printing scale: In actual engineering projects, it is not possible to create drawings that are exactly the same size as the physical objects. In other words, the AutoCAD graphic files stored on a computer are not yet actual drawings; they are merely electronic graphic files. To turn them into real physical drawings, it is necessary to print them at a 1:n scale. 1:100 printing means that a line 100 mm long is printed as 1 mm long. In other words, if a line 1000 mm long in the electronic file becomes 20 mm long on the printed sheet, then it is referred to as 1:50 printing (1000/20=50). For this reason, when using AutoCAD for drawing, it is more appropriate to think of the drawing scale as the scale at which the printout will be produced. 3. Physical objects have no scale; only non-physical entities have a scale. Since AutoCAD draws things at their actual size, physical objects therefore lack a scale. However, non-physical drawing information such as text, dimension annotations, and symbolic graphics. Originally, there was no such thing as a scale; yet AutoCAD does have one. Why? Because when electronic files are printed as physical drawings, a 1:n scaling is used, and all objects on the drawing must be scaled equally. In this way, text that is 5 mm high on the physical drawing must be set to 500 mm in the AutoCAD electronic file when the printing scale is 1:100, so that 500/100 = 5. In other words, during the drawing process, non-physical elements must take into account the scale of the drawing. This leads to a concept: since printing needs to be reduced by a factor of n, objects that originally lack proportion must first be enlarged by a factor of n. Correction: There is a misunderstanding regarding units mentioned above. A DWG file contains only graphic units; there is no such thing as a metric unit where 1 graphic unit equals 1 millimeter. Units such as millimeters, meters, and inches are set during printing – in other words, the units are determined at the time of printing; before printing, it’s only the graphic units that exist. 4. Scale in dimension style: The global scale factor for dimensions, which is the system variable DIMSCALE; the scale factor for measurement units, which is the system variable DIMLFAC; and the fraction height scale factor, which is the system variable DIMTFAC. Let’s start with the scale factor for measurement units – DIMLFAC=1, which is the default value. If we refer to the size values shown in the diagram as dimension values, then: Dimension value = Actual measured value × Scaling factor of the measurement unit. Through the above formula, it becomes clear that if we want to draw diagrams at different scales on a single sheet without using paper space, we must artificially scale certain elements. For example, if we need to draw an enlarged version at a scale of 1:25 on a base map with a scale of 1:100, we must enlarge those elements by a factor of 4; thus, a length of 1000 becomes 4000, and the dimension label would also be 4000. However, we don’t want the label to show 4000 – it should still read 1000. In other words, the actual measured value is 4000, while the dimension label shows 1000. Clearly, in this case the measurement unit scale factor DIMLFAC = 1/4 = 0.25. To speak generally, I don’t think it’s a good idea to avoid using this system variable and instead rely on input data or editing the data after it has been broken down. 5. Viewport ratio: This viewport refers to one that is created in the drawing space. Beginners may not have a clear understanding of what drawing space is, so let’s explain this concept using an analogy first. You write some words and draw some shapes on a piece of paper, then cover it with another piece of blank paper, and as a result nothing is visible. Make a small square hole in this piece of white paper, and you will be able to see part of the paper below it. As you increase the distance between these two sheets of paper, more and more things become visible, yet they also become smaller. The paper below is called the \"model space,\" the paper above is called the \"paper space,\" and that small square opening is called a \"viewport.\" The distance between two sheets, set via zoom, is the viewport scale. Note that the small square hole is there only for you to see; since a piece of transparent paper is stuck over the square hole, it is not possible to modify the content on the paper below through that sheet of paper. By lifting the transparent paper over the small square hole, a real hole is created, allowing you to insert a pen through it to make changes to the content on the paper below. This is called \"activating the viewport\". A small hole allows one to see everything on the paper below; this means that a small drawing can represent an entire building. By adjusting the distance between the two sheets of paper, and by drawing the frame on the upper sheet, whatever is on the lower sheet, no matter how large it is, can be accommodated within it. The distance is too great; if you want to see a specific area clearly, then make a small hole. Of course, you need to cut the paper so that the hole can be positioned closer to that area (ACAD does not require “cutting”). This way, different scales can be shown on the same diagram. Because it has the function of allowing different scales to be displayed, the Chinese version refers to paper space as “layout” as well. Obviously, with this feature, there is no longer a need to manually scale graphics when drawing them at different proportions on one diagram; all objects are drawn at a 1:1 ratio. When creating drawings in paper space, the natural printing scale is 1:1 (theoretically, it’s also possible to print at a 1:2 scale, but no one would go to the trouble of doing that). In this case, the viewport scale has nothing to do with the printing scale; rather, it depends on the drawing scale. Since it’s related to the drawing scale, different scales require different viewports, with respective viewport scales set accordingly. For easier understanding, we can use a simple analogy: in model space, the printer is used to adjust the scale of the drawings, while in paper space, AutoCAD adjusts the scale first before printing, so there is no need to rely on the printer. There is a saying: \"No matter what the scale is on a diagram, there is only one global scale factor, DIMSCALE.\" ” This is plotting in model space; at this point, we are plotting in paper space, so that statement is incorrect. When there are different scales on one drawing, it’s essentially as if it’s being “printed” from model space to paper space at different scales. As a result, the DIMSCALE value will not be the same. Fortunately, there is already a viewport scale available, meaning this “printing” scale is already set, so there’s no need for users to use DIMSCALE in order to avoid confusion. Therefore, in the dimension style, DIMSCALE is set to 0 (not specified). Do not set DIMSCALE, as there is no manual scaling; DIMLFAC remains equal to 1.0. In this way, regardless of the number of different scales in the drawing, only one dimension style is needed