Saturday, November 15, 2008

3D Drafting:My philosophy

Over the years, I have come up with a style of drafting in Autocad that suits me.

These are for plant layouts.

See what you think of these:

1. Do not draw holes in pipe flanges. This uses up memory, slows down display and so on.
Having them in may make the view more realistic. For plant layouts, I would hope that nobody in the whole world puts in nuts and bolts on a pipe flange.

2. Where possible, simplify! There is a great temptation to draw every curve on an item-resist it.

3. Don't go Layer Mad. I reckon you need layers named:
Level 1 Plant
Level 2 Plant
Level 2 Beams
Level 2 Floor
Piping (Sometimes I use the pipe label from the p and id- eg Pipe-54-102-44)
....and not a lot more. I work with a person who had the idea that one should have a layer called say Sifter, as it allowed him to work on that item easily by isolating that item. I say, if you want to work on such an item for a while, you are better off cutting and pasting that item into a new drawing all by itself and working on it there. Alternatively, assign it a temporary layer. I use about 5 main layers:
Dim: This is for all annotation, not that this is needed much any more as most items in paper space can be any old layer.
CL: For centre lines
Hid: for hidden lines, not used much for 3d
lgt:for light lines
med:for medium lines
Hvy:for heavy lines
pha: for phantom lines.
Your ctb file should allow for all numbers from 8 to 249 to be 0.2mm wide and colour black when printing. Numbers 250 to 256 should be colour by object, not black, so that on a laser printer you can show shades of grey.
I use the built in Layer Manager to save various states, but I guess layer filters would have the same end result.

4. Do not draw the fillets in on the structural steel. This is wasteful of time, energy and clutters the drawing up, making it harder to determine what is where in wireframe.

5. Do not draw the insides of things, for example, hollow sections, unless you are really keen on portraying the "real thing". I worked for one company, where it seemed that it was a badge of honour to show all the insides of a hopper-who wants to know?! The answer is sometimes you do like to show this, but please do not blindly apply it to every item so you can say your drawings are consistent. If you are a cad manager reading this, you could in theory speed up the throughput of your office manyfold, if you considered just this point carefully.

6. Keep your model pure. By this I mean: don't put text in model space, or sectional views, or parts details. Put these in their own separate drawing files, it is not much trouble and keeps things fast and tidy.

7. Write block out your sections to file called say 149993-sectionAA.dwg. Then in the drawing that you want that section to appear, Xref it into that drawing. The benefit of this is that when you make a change in the model, you can update the section file, which will automatically update the drawing it appears in.

Happy drafting!


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