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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.

 

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CAD Basics 101 – Scale factor Part 1

Scale factors – Wait… That’s basic?? Yes, yes they are. Scales or scale factors are used to provide a method for presenting a large area or small area on the desired media size that is readable by the end user. What does that mean? Well, a scale factor allows us to present our design to the people that will be fabricating or building it and present it on a piece of paper that they can actually hold. Scale factors can be found using good ole math. There are factors used in Scale Factors to size the things presented on your drawings accordingly. What does it mean to draw 1=1 (one to one)? Why draw one to one? I thought you said we draw so that it fits on a smaller sheet. Scale Factors tend to confuse more drafters that it should. They are actually quite simple to understand and apply, but if you don’t understand their purpose it can become confusing on knowing when and how to apply them.

Scales allow us to draw a building that is 60’ wide and 40’ deep and show it on a piece of paper that is 22” x 34” long (aka ANSI D-Size). CAD allows us some advantages over traditional drafting on the board. CAD allows us to draw full size (1=1) then scale our title block (border) around the full size (model) and then print it to fit (using proper scale) within the boundaries of a piece of paper. Board drafting required us to draw at scale. This meant that if you wanted to represent the 60’x40’ building on a 22”x34” ANSI D Size drawing, using 1/4” scale (1/4” = 1’-0”), you as a drafter would draw a line 15” long to represent a 60’ side of the building. That line is 15” regardless and it is on a piece of paper, or vellum, or Mylar or whatever media was being used. The point is, it was scaled, down, for the paper and not full size (1=1). With CAD we can draw in our real world model and create a building that is in fact 60’ x 40’, then scale our border up to allow the building to fit inside our border. This means our border is actually huge 136’ x 88’ in size. No at full size this will not fit on a 22”x34” sheet of paper. We can plot this drawing using a scale factor to make it fit on the 22”x34” piece of paper. Please note when applying scale factor for drawings we always use a scale that maintains aspect ratio. Not to confuse you, but that means whatever scale we apply to one plane of the drawing we apply to the other plane. On paper we have 2 planes, X and Y. Let’s do the math. 1/4″ = 1’-0”. First let’s fix the units so they match. There are 12” in a foot. So now our equation is now 1/4″ = 12”. For an equation to work we are apparently missing something.

Apparently it’s Algebra:

Next let’s verify our equation:

We now have a scale factor of 48. So what do we do with it? Our scale factor is used to calculate the size of something relative to the paper size to appear appropriately with the actual size of the drawing. Our title Block is 22”x34”, so if we multiply 22” x 48 = 1056” -> 1056” = 88’: 34” x 48 = 1632” -> 1632” = 136’ that is the size of our border in our full size model. Please note we are NOT discussing Paperspace….yet. Everything we are discussing is Model space at this time. This same principal applies to text and Symbols. If we want text to be 1/8”(0.125) tall in our drawing (model) then we would need to apply the scale factor to the text. 0.125” * 48.0 = 6.0” This means your 1/8” text would need to be 6” in height to print at on a 22×34 ANSI D Size sheet of paper. So what would the height of the text be if we plotted this same drawing to 11×17 (ANSI B Size)? Notice the sheet size is a 1/1 ratio scaled by half of an ANSI D size sheet of paper. That means the 1/8” text would now be 1/16” in height on the printed 11×17 print.

We will continue this in my next post…. Coming soon.

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CAD Basics 101 – TEXT

 

I won’t bore you with rants about some of the, let’s say, subpar drafting efforts I have seen over the years. CAD has become more and more advanced and feature rich over the years, and I feel drafting quality has declined. Let’s try and help turn that around. Starting with Text. Text is used to communicate to the person reading the drawing. It is important that we communicate effectively and consistently. Text is basic so here are some basics checks for text.

  • Is text spelled correctly?
  • Is the text clear in meaning?
  • Is the text uncluttered and not overlapped by other line work in the drawing?
  • Is text positioned correctly?
  • Justified and aligned correctly?
  • Is text the right height for the subject matter (Body, Heading or Title)?
  • Text Width?
  • Layer?

Is your text spelled correctly? It is easy enough to verify your spelling. Yes we all make typos and get rushed, but get in the habit of verifying your spelling. Is the text clear? Does the text present the message you are delivering. Abbreviations are used quite frequently in drawings, but you should avoid them if possible, remember the goal is to deliver a clear message.

Is the text uncluttered and not overlapped by other line work in the drawing? Your text should not overlap or be overlapped by other elements in your drawing. Your text should be located in a spot that allows for text to be uncluttered. If your location does not allow for clean placement, you may need to break some of the background out or consider using a wipeout or text mask. I you choose wipeout or text mask methods, make sure you have good standards in place and have communicated the proper process for using them. Remember the printed result is what is used. If your system requires special settings for printing some of the issues that arise from wipeouts and text masks, then it is highly likely someone will print it incorrectly.

Is text positioned correctly? Your text should be relative in position to what you are identifying. A leader that stretches across 3” of printed material could easily lose its association. We will cover Leaders in another post. Is it justified and aligned properly. If you are like many CAD users, you simply copy other text in the drawing, change it and move on. This practice works great, but make sure the text you are copying is right to begin with. One of my personal favorites (read sarcasm) is when I copy a few lines of text, I then update that text, and then suddenly instead of it shifting as it should. The text actually changed position from where it should have been justified. For instance. It looked like it was centered, then when I changed the text to be longer or shorter, I discover it is Left justified. This is easily fixed, but, shows poor quality work on someone’s part. Make sure your alignment is correct. If you are placing an equipment tag inside an equipment outline and it fits centered and looks clean, great. If it is on the left or right of the equipment, Should it be left or right justified, these are things to look at. It may sometimes work, but it may also get confused with another piece of equipment. Check the presentation and make sure it is clear.

Is the text the right height, weight, width for the subject matter? Standards are what dictate these things. You should have some. If you are unaware of them, then ask. Text heights, weight, and width are often controlled by the text style. Text styles are a great way to maintain a consistent look in your drawings. Get to understand them. Note that text height and width are controlled at the text entity level and not the style level. The style simply sets the default for those. Text weight can be controlled in a few ways, Layer, color and by font selection. Again consult your standards on these. If the text is on the correct layer, you probably have the weight right. If the Font is set by the style correctly, you probably have the weight right. Color based plotting can control the weight as well, so keep in mind the best practice is to always draw bylayer for your color setting and not use the color setting at the entity level. Yes there are occasions when you should deviate. We will save bylayer topic for another post as well.

Some of you will relate to this topic, and think yes I wish more people understood this. If this is the case, forward this post on to them. Share the knowledge. I have found that typically most CAD users want learn and improve their skills. I’m sure all of us have opened a drawing and thought, “WHAT WERE THEY THINKING?” Some CAD Users are learning, CAD Systems like AutoCAD, have become so feature rich and full of functionality, often times new users are overwhelmed and not sure what the correct approach or setting should be. I am hoping to post more on CAD Basics on a regular basis. If you find these useful please share, comment or like. Thank you for reading.

Have an amazing day!