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CAD Basics 101 – Scale factor Part 3

Now that we know how to get a scale factor for our drawing, how do we know which scale to use? Luckily there are standard scales to be used. Engineering, Architectural, Metric are some of the more common ones in use and are actually physical tools for measuring distances on actual drawings. If you have been in design or drafting for any length of time you have seen one. These are standards that we need to maintain and use. Yes we could make up our own to better suit our drawing or fit closer to the title block size, BUT we will avoid doing that, as it will cause problems and issues later.

One of my favorite sayings is “Just because you can do something, does not mean you should.” This is also why I am writing these blogs, to help educate some of the best practices in our industry and hopefully help my readers better understand and share the purpose of them.

Let’s talk Architectural Scales: You have heard 1/4″ = 1’-0” in my previous posts. That is an Architectural scale. Pretty easily to identify as it has inches and to a foot ratio. Here they are:

Standard Scales Scale Factor Inverse Scale Factor (used in paper space)
3” = 1’-0” 4 1/4th or 0.25
1-1/2” = 1’-0” 8 1/8th or 0.125
1” = 1’-0” 12 1/12th or 0.0833333
3/4″ = 1’-0” 16 1/16th or 0.0625
1/2” = 1’-0” 24 1/24th or 0.0416667
3/8” = 1’-0” 32 1/32nd or 0.03125
1/4″ = 1’-0” 48 1/48th or 0.0208333
3/16” = 1’-0” 64 1/64th or 0.015625
1/8” = 1’-0” 96 1/96th or 0.1041667
3/32” = 1’-0” 128 1/128th or 0.0078125
1/16” = 1’-0” 192 1/192nd or0.00520833

 

We will get to Paperspace next post, but I wanted to list those values used in paper space here.

Engineering scales are recognized by 1” equaling a multiple of 10’. Standard Engineering scales are:

Standard Scales Scale Factor Inverse Scale Factor (used in paper space)
1” = 10’ 120 1/120th or 0.0083333
1” = 20’ 240 1/240th or 0.0041667
1” = 30’ 360 1/360th or 0.0027778
1” = 40’ 480 1/480th or 0.0020833
1” = 50’ 600 1/600th or 0.0016667
1” = 60’ 720 1/720th or 0.0013889
1” = 100’ 1200 1/1200th or 0.0008333
1” = 200’ 2400 1/2400th or 0.0004167

 

Metric Scales are pretty nice as the metric system is based on factors of 10. Metric Scales offer something the other scales don’t. You can mix and match the units as they fit your need. Typically they are used as in mm to meters, but can be adjusted to be any metric distance measurements to any metric distance unit. Common Metric Scales are (using millimeters to millimeters to avoid any confusion:

Standard Scales Scale Factor Inverse Scale Factor (used in paper space)
1mm = 20mm 20 1/20th or 0.05
1mm = 25mm 25 1/25th or 0.04
1mm = 50mm 50 1/50th or 0.02
1mm = 75mm 75 1/75th or 0.0133333
1mm = 100mm 100 1/100th or 0.01
1mm = 125mm 125 1/125th or 0.008
1mm = 200mm 200 1/200th or 0.005
1mm = 250mm 250 1/250th or 0.004
1mm = 300mm 300 1/300th or 0.0033333
1mm = 400mm 400 1/400th or 0.0025
1mm = 500mm 500 1/500th or 0.002

 

Keep in mind if you start mixing the metric units, you will need to increase or decrease the values in the table accordingly. For instance if you said 1mm = 1m that would not b1 1=1 that would be 1 = 100. So if you applied the same 1mm = 100m scale you would need to increase the value in meters to be 10000. Because there are 100mm in every meter. So keep that part in mind the above table is mm to mm.

Note: There are different units you can apply to your drawing as well in AutoCAD. The system Variable INSUNITS controls what unit setting your drawing is using. You can access it or change it easily via the UNITS command. This allows AutoCAD to automatically apply unit conversions when inserting or referencing different drawings into your drawing.

Now we see a number of different STANDARD Scales we can use in our drawings. Stick with these and it will improve the quality of and make your drawings easier to use and manage.

A few reasons:

  • Industry standards already in place
  • More likely to have tools, physical and automated systems are more likely to work with standards
  • Drawing quality and consistency

Next up is Paperspace and how all this comes together.

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CAD Basics 101 – Scale factor Part 2

So, we have a Model needs a border with a scale factor of 48. Where else do we use this scale factor? Symbols, Text heights, Dimensions, Leaders, Linetype scaling, line work settings, Grid and snap settings and don’t forget plotting your drawing, and more I’m sure. I won’t go over every possibility, but will cover some to make sure we understand the concept. In another post I will help those of you that are wanting to learn more about automating with AutoLISP or other AutoCAD API’s, develop your own setup commands to help set drawings up consistently and take some of the headache out.

A Symbol is typically something that is used in drafting to represent something that otherwise might not stand out in a drawing. Things like a North Arrow, Section Marks, Material Bubbles, Receptacles, Lights, Welding callouts, and so much more. If your standard North arrow is 1.5” long on your drawing, then you want it to appear that way on every drawing. I will write another post on which way is up later, lot of debate on something that should be simple. Back on track… The North Arrow will be scaled consistently in your drawing to match the scale factor of the title block you are using or the scale factor of the drawing as established earlier. Keep in mind we are still not discussing Paperspace. We are focusing on understanding model space for the time being. It is also a good practice to maintain a position relatively close to the same spot on the drawings. You figure out the distance and the multiply that by the various scale factors of your drawings and they all come out the same, regardless of scale. It is important to start with a 1=1 drawing and figure out where it goes.

Text can get a little more depth, but it is the same principal as we discussed in the previous post. Take the desired plot size for the media you are printing to. Multiply that by the scale factor and that is the height of your text. I highly recommend setting up styles for each text height. At one point we had Leroy styles to match as close as possible to the Leroy pen sets that were used in manual drafting. This concept was very beneficial, because, when pen plotters took forever to plot a drawing, the occasional word being misspelled could be picked up by a manual drafter instead of sending the drawing to the plotter again and waiting 30-60minutes, and wasting ink and paper. Today’s printers take seconds to print, so that is not much of an issue any more. Another method of just using text styles like T125 for 1/8” text T25 for 1/4″ text has been around for a while. The 125 and 25 being the decimal equivalents of the fractions.B125 would represent Bold text and could either be a different font, or just simply shown on a different layer that plots with a heavier pen setting to make it stand out.

Let’s move on to Linetype scaling. If you load a linetype into your drawing, you will notice it shows up pretty good in a base drawing, but what happens when you draw that line in a drawing that has a scale factor of 48. That line was designed to be displayed in a drawing of 1=1, so at a scale of 48 it is pretty much too small to see. In AutoCAD there is a system Variable called LTSCALE. I have seen LTSCALE set at 1.0, 0.5, 0.375, and even 0.25. What does that mean? Well LTSCALE is a factor applied to the dashes dots and parts that make up the linetype. LTSCALE applies to all lines in the drawing. Line definitions are stored in the drawing file once loaded, so keep that in mind when you are trying to track down why two drawings are different looking. They may actually have different linetypes loaded for the same name. Using 1.0 for our test case we discussed last post would mean out LTSCALE should be 48.0. If we had a standard setting of 0.5 LTSCALE, then our LTSCALE would be 0.5 * 48.0 = 24.0.

NOTE: CELTSCALE is not the same as LTSCALE and something that should be set and stay set at 1.0. Nothing worse than tracking lines with individual settings of an LTSCALE. Yes entities can have individual LTSCALE settings, not a good idea to use this feature as a normal process.

Grid and Snap are important drawing tools to help you draw more consistently and accurately. If you are drawing in a 1=1 drawing like a wiring diagram, P&ID, Or even a legend sheet, you will find your snap settings are pretty simple, something like 1/4″ grid and 1/16” snap. This allows you to have snap points between the grid points that are always 1/16” apart. This keeps you consistent, and often keeps your fellow CAD designer Drafters happy. We will cover proper use of these in another post. Will snap and grid setting work in a drawing that has a scale factor? Of course it will. But keep in mind sometimes, dimensional data may force you to draw off grid and off snap. Parts are manufactured all over the world and dimensional data isn’t always cooperative from vendors. Make use of these tools. To use them in your scale factor drawings simply multiply the scale factor by the typical/standard setting and you have your new value.

That is all for this post. Next post we will cover Industry Standard Scales and why you should not make up your own. Good luck and thank you for reading. Sign in and leave some comments, or ask questions.