First and Third Projection Symbols

[GreenTwin]

One thing I never do on drawings (or at least try to avoid) is playing guessing games.

I have a wide array of folks from all different backgrounds who look at and review my drawings, and they need to be crystal clear about what is what exactly.
The people looking at my drawings could be engineers, managers with little technical background, vendors, maintenance personal with good technical skills but poor drawing-reading skills, etc.
Everyone of these people should be able to clearly understand what the intent of my drawings are, and what the limits of work are.

I never assume that anyone knows anything as far as who gets my work drawings, and yet they should still be able to get an accurate takeoff, or know exactly where every wire terminates.

I just explicitly state everything.
Just takes a second, and saves hours if someone misinterprets something.

I missed one word on a drawing a few years ago, and one bidder was 1 million off because of how he interpreted my incorrect word.
Luckily we got to rebid the project for another reason.
Extreme caution is a must in my business.

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[Curious1]

This has been an enlightening discussion. Thanks Green Twin for raising the question and all others for the responses. I have often wondered why I struggle with some drawings and not others. This points out one possible source of my issues.

 

[Richard Hed]

As for why some peeps might put various drawings seemingly in the wrong place, there actually are several reasons this might be done.

The one reason might be that the dwgs might be in order of ease or necessity of machining.

A second reason, and ujsually the one I follow, is to group the parts into related categories, e.g., cylinder parts, parts placed on the crank shaft, steam inlet body, steam valves, exhaust valves, governor, miscellaneous.

The last reason and IMNSHO, not a reason at all, because there is space on the page for another small part.

I'm sujre there are other reasons.

 

[user 52078]

My Dad was an architect, I trained as a professional mechanical engineer, most of my working life has been spent in product design, in drawing offices, running drawing offices.
Time to fess up - I have worked in 3rd angle for decades but still put drawings down and find that I have instinctively drawn it in 1st angle. Lucky for me I can just shuffle the views about in CAD and nobody is any the wiser. So keep it to yourselves.
Martin

 

[peterl95124]

Mr Green, I could not agree with you more !

"first/third angle projection" doesn't have anything to do with angles :-(
and those cone symbols are just hieroglyphics :-(
and IIUC its only the brits that use "1st" and they drive on the wrong side of the road if you get my drift :-(

like you, if there's anything unclear about the placement of views I label them !!!

Pete "maybe I got out of the wrong side of the bed this morning" Lawrence.


PS, I'm grouchy this morning because I've had to work out using linear algebra and trigonometry what rotations are needed for dimetric and trimetric views that result in specific/given drawing angles, and what foreshortening factors to apply. if anyone has a reference to a book that has the foreshortening factors for common drawing angles that would be appreciated, as I'd like some confirmation/validation of my calculations,
typically
isometric 30-deg and 30-deg 1 : 1 : 1
dimetric 7.5-deg and 45-deg
trimetric 15-deg and 45 deg 0.916 : 0.650 : 0.857 ???

(IMCAC, this trimetric is the result of 27.5-deg Z-rotation, and 31-deg X-tilt)

 

[Jasonb]

Not just us Brits but Europe and the rest of the world, it is just the US and Canada that tend to use 3rd angle in a similar way that they do with inches

 

[Gordon]

I never realized that there was such a thing until I was working on a drawing that someone else had drawn and I could not understand how the piece was made. Everything was backwards to my thinking. Things that should have been shown with hidden lines were solid and solid lines were hidden. I finally did some investigation and was told that there were different standards. I was taught that you looked at the front view and folded the other views away from you. The other method folded the views toward you. Now I take a careful look at drawings not made in US. I am not sure of what countries use what method.

 

[Jasonb]

One other thing to watch if you are not aware of conventions is that if you choose a drawing template from your CAD package it may well pick a projection angle based on the templete.

For example, if you pick ANSI and letter size paper you may find it defaults to 3rd angle as US uses ANSI and that format paper. If you pick ISO and say A4 paper it may default to 1st angle as contries who use the ISO system use 1st angle. Two of the same engine here one on ANSI template, The other on ISO and the package has used different projections.

 

[GreenTwin]

I pull everything from Solidworks 2D drawings back into Autocad.

I don't try to use Solidworks for 2D drawing work; it is just too clunky.

And so I set my sheet size inside of Autocad.

With no sheet size selected in Solidworks, I can drag projections out from a central figure up, down, left, right, or at 45 degree angles in any of four directions for isometric views. I think I can also project from a projection face.

So my Solidworks drawing looks like the one below, and I pull that back into Autocad.

I never do less than top, bottom, left, right, and one or two isosmetric views, unless perhaps it is a simple part, not an assembly.

It does appear that Solidworks puts the top view below the central figure, and the bottom view above the central figure, which is counter-intuitive for me.
Left and right views are not really definable unless you define what view is front.
In the case below, if you call the central figure the front view, then it is actually showing the left view on the right, and the right view on the left.

At any rate, I rearrange the layout when I put it into Autocad, to use my standard arrangment, which is 1st angle I guess.

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[Jasonb]

Rather than have Solidwarks lay it out as 3rd angle why not change the default to the 1st angle you prefer?

https://help.solidworks.com/2012/english/solidworks/sldworks/HIDD_DRAWING1.htm
Then you can confuse all your fellow Americans

 

[peterl95124]

Not just us Brits but Europe and the rest of the world, it is just the US and Canada that tend to use 3rd angle in a similar way that they do with inches

we draw the side view, then the top view above that, then the right side view to the right of that, that's the logical way. I have no idea what demon possessed the minds of the people that came up with the other way, perhaps it was the result of a "committee" decision (a choice that offends everyone equally) :-( ?

 

[Charles Lamont]

Not just us Brits but Europe and the rest of the world, it is just the US and Canada that tend to use 3rd angle in a similar way that they do with inches

Er, are you sure? Historically 1st angle may have been prevalent in the UK but throughout my engineering career, since tech drawing class in first year uni in the early '70s, the convention has been 3rd angle. I have a Stuart Turner drawing in front of me from 1958 that says it is in 3rd angle.

 

[GreenTwin]

Then you can confuse all your fellow Americans

I can confuse myself by helping to confuse others......LOL.
I would be good at that.
One must have some talent doing something.

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[GreenTwin]

I have a partical set of drawings for the side beam steam engines of the naval vessel Mississippi, drawn by James Copeland in 1840.
They are very good examples of how to never draw an engine.

I also have drawings of an almost identical side beam engine, drawn by the French, and they are excellent examples of clear and concise engine drawings; also created in 1840.

You have to be a very good detective to use the Mississippi drawings.
Not much on them is labeled or obvious.

I will try to post examples of these two engines.

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[GreenTwin]

we draw the side view, then the top view above that, then the right side view to the right of that, that's the logical way. I have no idea what demon possessed the minds of the people that came up with the other way, perhaps it was the result of a "committee" decision (a choice that offends everyone equally) :-( ?

I have been in committees, and I can honestly say that I have never seen anything good come out of a committee.
They are a place for folks to practice politics and use power plays and intimidation to try and dominate others.
Committees are the polar opposite of good engineering design.

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[HMEL]

I have been drawing professionally for 29 years, both manually on the drawing board, and on computers.

Recent discussions involve mixing up symbols for first and third projection.

I have to admit I have never used these symbols, and would not know what they look like if I saw them.

Can somebody post a drawing that shows those, preferably a model engine drawing.

Thanks,

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It has always been my philosophy and it is what I was initially taught that a drawing conveys information. What information you present my be dictated by the drawings purpose. Standards exist to help others understand the meaning. However there were times when I made the drawing for myself and these were often filled with notes and technical clarifications that would have meaning only to me.

Now over the last few years thanks to cad symbols have proliferated like rabbits. How they are used and what they are used for varies but usually a good layout does not need symbols.

 

[JohnBDownunder]

This old fella went to school where we drew, Plan (looking Down), Side elevation (Looking from the side you place the sketch). Then, Front and or Back elevations.
Model club member explained 3rd angle to me as putting the part in a bowl then when you slide the part up either side, back or front that's what you should see. Now looking at the previous posts it's probably wrong. Ah well!

 

[Jasonb]

Charles, could be the subject as 1st angle was what was used at my College but that was architectural drawing.

Quick look through the last couple of Modle Engineer mags shows both projections being used with more in 1st angle than 3rd. At a ratio of about 2:1

I've got Reeves (80s) and Anthony Mount drawings (10s) both 1st angle

 

[GRAUBELE]

Hello everyone

Very interesting topic that I am following with attention.
Maybe I can contribute something with a scan from one of my (printed 1977) metal specialist books.
Sorry, it's written in German, but I think the sketches are self-explanatory.
I would like to give you a little hint, here and now after I have left my professional life, now in the hobby area something cannot be presented according to the norm, the main thing is that I understand the big picture.

Regards
Dieter

 

[GreenTwin]

Some translation:

anordnung der ansichten und schnitte = Arrangement of views and sections

untersicht = bottom view

draufsicht = top view

ruck-ansicht = means back side, or looking from behind (rear view)

seiten ansicht von links = side view from left

seiten ansicht von rechts = side view from right


vorder ansicht = front view

schnitt = cut (section)

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