Query on Plant Layout drawings 2

[sudhakarn]

Hi folks,
I have a small query on creating Plant layout drawings in AutoCAD. I just wanted to know how to start and proceed big drawings( in metres) such as Plant Layouts.My doubt is on setting the drawing limits, Plot scale (for plotting the drawing on an A3 sheet),if the drawing is given with a scale of 1:30 ,should I use the scale command.how do I manage the annotations and dimensions sizes for such drawings in print?

Can you please detail me on proceeding for such a drawing from scratch to Print?

Thanks in Advance.

 

[dik]

I'm a big supporter of 'tinkering' and I think too few people do it these days... once you have a working drawing in both model and paperspace, it's a matter of changing a few things, moving a few things around, etc. just to become familiar with the cad program.

As a caution, it is possible to change the original model from paperspace, so be careful and 'lock' your viewports.

Dik

 

[sudhakarn]

Hi folks,
In continuation to this, I just want to clearly understand the concept of defining limits in an AutoCAD drawing.
For example, I can draw any drawing of any size (which is in metres or MM) approximately and proportionally without any specific dimensions and I can take a print on any size. What is the significance of setting the drawing limits for a drawing? How does it affect my drawing sizes and Print sizes? Need more clarity on this topic please.

 

[IFRs]

I don't use limits at all. I draw full-size, full-scale in model space. I draw in inches, decimals or millimeters depending on how the actual construction is measured. Only parts go in model space, everything else in paper space. I scale viewports in paperspace either for clarity or to specific scales if people will scale off the drawing in the field.

 

[sudhakarn]

Hi IFRS,
Thanks a lot for your insights.I expect few more replies from our experts on this.

 

[dbill74]

A note about scales not mentioned yet.
After you've settled on a paper size you are going to use and have your border setup, you then know the biggest viewport you can fit on a sheet. Ideally, you will want to use the biggest viewport you can leaving room for notes, legends, keyplan, etc.

Once you have your basic viewport set, you can set your scale. The scale of your viewport(s) should be the smallest possible to fit your plan within the confines of the viewport AND be a standard scale. If you find that the drawing is illegible when showing the limits of the plant consider breaking things up and show only a portion of the plant on a sheet. This doesn't mean breaking up the model space drawing, just show a portion of the model in each viewport on each sheet. There is no limit to the number of sheets you can use, use as many as is necessary, a few years back I had a project that used about 20 sheets. The important thing is that the plans are legible. (And the same scale from sheet to sheet.)

A "standard" scale being a scale found on your desktop scale and fall into one of two types architectural and engineering. In my work, I use almost exclusively Architectural scales (1/8=1'-0", 1/4"=1'-0", 3/16"=1'-0", etc) so am not that familiar with all the standard engineering scales although 1:30 does look like one.

 

[IFRs]

Standard scales are only needed if a user will use paper copies of the drawing and wants to measure things on the paper. This assumes of course that I know the printer they are using, their paper size and available print area, and that they are not using a copier or printer that arbitrarily prints to fit or copies not quite 1 to 1. Half of my clients never do this - they are machine or fabrication shops, their drawings are always B size 11 x 17 with viewports scaled for clarity, I zoom in to details without the need to restrict myself to standard scales.

 

[sudhakarn]

Hi,
Thanks a lot for your insights IFR and Dbill74 .very useful information. What I understand is that the plot scale of 1:1 is not mandatory in all cases and that the drawing just needs to be legible enough.
So can we conclude that the drawing limits we set is used for setting the sheet size on which we would be plotting?

 

[sudhakarn]

Hi folks,
Any conclusions or inferences to this topic "Limits"?

 

[MikeHalloran]

I suggest that limits are an artifact of a time long ago when they served a purpose, and no Marketeer will ever remove a 'feature' from a product, even if no one needs it or even knows what it does or once did.



Mike Halloran
Pembroke Pines, FL, USA

 

[IFRs]

IMHO the only value of setting limits is that AutoCAD prevents you from putting objects outside the drawing limits. This can save you from from oopsies down the road.

 

[sudhakarn]

Hi,
Nice to see your replies.I just want to understand the concept of units in AUTOCAD. If I set the insertion units to metres,then is it that I am setting my current drawing units to metres.
How does the plotter or print recognise my units if it is in metres or MM.

 

[IFRs]

The plotter has no clue what the units are. Autocad creates a plot file of whatever you tell it to - Display, Limits or Window - and streams that to the printer. You decide what objects are included in the print job, the paper size, how they are scaled and any X or Y offset etc.

 

[sudhakarn]

Hi IFRs,
Thanks for your prompt response. Say if i draw a line for 5metres and plot it on an A3 sheet with a plot scale of 1:1,then what is the result I can expect on the plot?
By the way could you please clarify me on the concept of units in AutoCAD?

 

[Sparweb]

Hi Sudharkarn,
There are multiple places you encounter so-called "units" in AutoCAD, so I'll discuss the three that come to mind:

The command line UNITS defines the number of decimal places that will be shown on all coordinate readings, measurements, and distance calculations.

The dimension style dialog box can also define a parameter that will convert the measured values in the dimension lines. This parameter can be anything you specify, but by default will probably multiply the basic measurement by "25.4". It can easily be changed to "0.3048" or something else that is useful.

The printer dialog shows the scaling units to be used when printing the drawing, which is the ratio of the selected area to plot to the area available to plot on the paper.

Note that NONE of my descriptions have involved the terms "meters" or "inches" or "millimeters" or any term of measurement whatsoever. AutoCAD does not know what they are!
I repeat, there are NO UNITS OF MEASUREMENT in AutoCAD. All appearance of using units, such as the dimension styles, is just printing of letters such as "mm" after a result - not due to AutoCAD having any knowledge that the measurement is intended to be millimeters. Same goes for dimension expressions of feet/inches with the '/" characters - it all just a bunch of factors and multiples to be calculated, not a reflection that one drawing is "imperial" and another is "metric".

The closest AutoCAD gets to using actual real-world measurement units is the printer dialog - but even there it's just arbitrary. I had a lot of school friends who would constantly over-think the whole thing.

STF

 

[IFRs]

sudharkarn - Here is an example. In a new drawing, in Model Space, draw a line from 0,0 to 5,0. In your mind it is 5 meters long. Autocad only knows it goes from 0,0 to 5,0. Autocad does not know if it is 5 angstroms or 5 light years long, nor does it really matter. Now let's plot it. In the plot dialog, choose "Center the Plot" for the plot offset and "Extents" for what to plot. Autocad will print everything in Model Space centered on the paper. Now choose a paper size, for now choose ANSI B. Now look at the plot scale options. If you choose "Fit to Paper" it will scale the 5 unit line to fit on the paper. The plot will be a straight line across the paper, starting and stopping at the paper margins. If you choose 1 inch = 1 unit it will try to print a 5 unit long line on ANSI B size paper which will be 5 inches long and will not use all the paper. If you choose 1 mm = 1 unit your 5 unit long line will print 5 mm long and again will fit. If you choose 1,000 mm = 1 inch you will see a small portion of the line because your line is 5 units long, each unit is being plotted as a meter and your paper is much smaller than a meter. Try this a few times with a more useful drawing.

 

[sudhakarn]

Hi folks,
Excellent!Now I feel enlightened and now it's time for the practical experiment.Thanks a ton your detailed insights.

 

[dik]

I often add a scale 'bar' to drawings. This shows the 'length' of a foot or unit. When drawings are plotted to 11x17, you can get an idea of what a foot or 10' looks like on the plan.

Dik

 

[IFRs]

dik is absolutely on point. I do the same thing, even if the drawing is meant to be scaled off of, just in case it is printed on a different device or different size paper.

 

[sudhakarn]

Hi Folks,
Brilliant!Very much helpful ideas that will make any one's day.

 

[MikeHalloran]

I used to work in a fancy sheet metal shop, where we made our own tubing because the best material was available only in sheet form. Because of the nature of the product, we then faced the task of fabricating elbows and tees with branches at very odd angles, for which purpose we produced full size templates for cutting blanks or trimming tubes.

After scrapping too many thousand dollar sheets of Six-Em-Oh, I changed our procedures so that each template drawing file included a dimension between two targets, that was to be measured on the actual template, and initialed, before the template went into the job folder for fabrication.

The problem first came to my attention a long time ago, when I detected a three percent change in length in a diazo contact print vs. my carefully drawn vellum. That was long before CAD and printer/plotters, which allow an awful lot of opportunities to erroneously 'fit' an image element where you didn't intend to change it.



Mike Halloran
Pembroke Pines, FL, USA