topic Re: Help With Scale in AutoCAD Forum

Help With Scale

ethangannon2020 — Fri, 05 May 2023 12:55:40 GMT

Hi there,

I am new to AutoCAD and am having difficulty with understanding scale.

I know how to change the scale, and usually my drawings are 1:100, 1:500, 1:200, as I work with topographical drawings of large sites. But sometimes I get a drawing from a land surveyor and the drawing is 1:1 in model and 2:1 in paper space, but the title block says 1:500. Does this make sense?

When I set the scale at 1:500 it zooms way out, making the drawing minuet, so obviously the person has scaled the drawing way down, hence why it is now 2:1, but I don't understand why the person has put 1:500 in the title box?

Any help would be greatly appreciated.

Thanks

Re: Help With Scale

Patchy — Fri, 05 May 2023 13:20:34 GMT

Why trust the title block? put a scale on the drawing and find out.

I doubt that you got a drawing from a land surveyor and the drawing is 1:1 in model and 2:1 in paper space

Even if he surveyed a room, how big your paper will be to plot it?

Re: Help With Scale

ethangannon2020 — Fri, 05 May 2023 13:25:19 GMT

Thanks for you reply. I don't know how to put a scale on it. I know the drawing is tiny, because at a scale of 1:500 it zooms out so far that I can't see it, so in the past I have just highlighted the entire drawing and with my mouse scaled it larger so that it fits in my 1:500 viewport, obviously this isn't accurate either. I don't know what I am doing 🙂

Re: Help With Scale

Patchy — Fri, 05 May 2023 13:29:29 GMT

Title block can list anything, put a bar scale and find out.

Re: Help With Scale

ethangannon2020 — Fri, 05 May 2023 13:36:51 GMT

Will do, thanks. So is it possible for my bar scale to say that it is 1:500 even though the viewport scale says that it is 2:1? Sorry if that is a stupid question.

Re: Help With Scale

Patchy — Fri, 05 May 2023 13:42:51 GMT

It can be if the paper size had been scaled up, then the zoom factor of the viewport will not be correct.

Old surveyors done it before and I've seen it.

Re: Help With Scale

ethangannon2020 — Fri, 05 May 2023 13:43:55 GMT

great, thanks. I believe this is the problem, because it is unlikely that multiple architects and land surveyors keep putting the scale at 1:500 when it is 2:1 - 2:1 doesn't even make sense if it fits on a page. cheers

Re: Help With Scale

Wojty1 — Wed, 10 May 2023 16:49:03 GMT

Hi @ethangannon2020

Many years ago I wrote a short tutorial for students to better understand the scaling concept in AutoCAD products, but it was in German, so I will translate it for you.

Let's start with the basics. Since AutoCAD started as a CAD tool in the mechanical sector in the 80's, scaling like it's known in Civil Engineering and Surveilling was not relevant (for example 1:500 meaning 1m in the drawing equals 500m in the world). It rather used a totally different approach using a huge amount of units, even something exotic like Parsec or Angstrom used in Astronomy.

AutoCAD uses a combination of Drawing Units (DU) and Paper Space Units (PU) to get the final scale.

The default values in the Metric AutoCAD Product family are Meters as Drawing Units and Millimeters as Paper Space Units which result in the following standard formula to calculate the Scale (S) as 1 : S.

Scale factor x = (DU/PU) * (1/S)

So if you need a Scale of 1 : 500 then S = 500 and x = (DU/PU) * (1/S)

x = (1[m] / 1[mm]) * (1 / 500) = (1000[mm] / 1[mm]) * (1 / 500) = (1000/1) * (1/500) = 1000 / 500 = 2

So x = 2 and therefore the actual resulting Scale is 2:1 for a 1:500 display.

I know it's very confusing, but maybe now you get an idea of how Scales in AutoCAD work.

Please let me know if anything's still unclear.

Re: Help With Scale

ethangannon2020 — Wed, 10 May 2023 17:12:22 GMT

Thanks for that. Too be honest, I don’t understand how to apply this formula, but obviously people who are proficient in CAD do, and they understand what they are doing when they say the drawing is 1:500 but paper space says 2:1. I will never be creating my own drawings from scratch, I merely add layers to someone else’s drawing, so now that I know that this discrepancy makes sense, I am happy to just go with what the drawing says. Thanks again