First and Third Projection Symbols

[Charles Lamont]

I use 3rd angle because I grew up with it. 1st angle does have a slight advantage in sheet layout. Three orthogonal views are often necessary and sufficient. With 1st angle, the plan goes below the side elevation, and if a view of the left hand end (so drawn to the right of the side elevation) suffices, then the views fit better on a sheet that has the title block conventionally placed on the bottom right. Even so, 3rd angle wins because it more intuitive - FACT!

 

[GreenTwin]

I guess it depends on what you got use to using.

Sort of like Imperial/Metric.

I can't think in metric, but I know many who can easily do that.

I think in inches/feet/yards.

Long live 4x8 plywood !

.

 

[gbritnell]

Being in the States I was taught and use 3rd angle projection. That being said I was familiar with first angle from working with English casting kits. While working at Ford they had outsourced work to a company in Spain to build some patterns and core boxes. All of their drawings were 1st angle. If you are proficient with drawings then it only takes a short time to acclimate yourself.

 

[GreenTwin]

And if you are a total dumby like me, you will work for 38 years, and never even notice that there is more than 1st angle projection.

I have always just looked at drawings, and used them, in total ignorance.

Well, ignorance can be bliss, in some ways I guess.

.

 

[Gordon]

And if you are a total dumby like me, you will work for 38 years, and never even notice that there is more than 1st angle projection.

I have always just looked at drawings, and used them, in total ignorance.

Well, ignorance can be bliss, in some ways I guess.

That is also the case with me. I made drawings my whole life and did not realize that there was 1st and 3rd projection until I retired and ran into drawing made "backwards". The first time it really confused me. I thought that the designer had screwed up.

 

[GreenTwin]

The shop drawings I get these days are always computer generated, and often the equipment has been developed in a 3D model.
The accuracy is better than what I saw in the ancient times BC (before computers when I started working), and the modern 3D generated isometrics are fantastic, especially in color.

I think the 1st and 3rd projection thing is somewhat a relic of the past, in that a glance at the 3D generated isometrics tells you pretty much everything you need to know, regardless of how the drawings are laid out.

Most buildings are designed in 3D now, and you can fly around the outside, follow a path all through the building, go through walls while on the path, and turn walls transparent. For complex industrial facilities with lots of equipment and piping, the 3D building model is worth its weight in gold.
In the old days, there were a lot of conflicts during construction, and there is no reason to have conflicts these days, since you can see a complete virtual model of the entire building/process before construction even starts.

.

 

[DKGrimm]

And to think I've gone through almost my entire life thinking that I was the only one who always struggled with keeping views consistent -- and have a bunch of mistakes to prove it.

Don

 

[peterl95124]

And to think I've gone through almost my entire life thinking that I was the only one who always struggled with keeping views consistent -- and have a bunch of mistakes to prove it.

Don

I always struggle keeping my machined parts consistent with my drawings, and have a bunch of mistakes to prove it !!!

 

[peterl95124]

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

View attachment 153297

Dieter,
this is a great start, knowing that 7, 42 are standard(?) degrees for dimetric,
this seems to match what Kozo uses in his book ("Penns A3 Switcher"),
but what's missing are the scaling factors along the axies,

suppose the part measures 100mm along the "C" (42-deg) axis, what length do you draw it ? and what about the 100mm height along the "B" (vertical) axis ?

suppose the part measures 200mm along the "A" (7-deg) axis, what length do you draw it ?

I've used euler angles and rotation matrices and trigonometry and algebra to figure it out, but would like to see my drawing factors verified by something in a book some day !!!

Peter.

 

[GRAUBELE]

Hi Peter

we are talking about this section of the picture.

Here I make the translation from the German text:

Application:
If important things are to be shown in the front view.
Dimensions in directions A and B = scale size.
Towards C = 1/2 scale size

For your example:
Direction to A (7°) = 100% of dimension (200 mm = 200 mm in drawing)
Direction to B (90°) = 100% of dimension (100 mm = 100 mm in drawing)
Direction to C (42°) = 50% of dimension (100 mm = 50 mm in drawing)

I hope, it is clear described?
If you have any further question, please do not hesitate to ask.

Regards
Dieter

 

[ssaxer]

Many years ago when I was in school we still made drawing by hand (we used Autocad 2 for CAD work). I was taught that for 3rd angle drawings you made you views as if you were outside the box looking in and 1st angle drawings were made with your views named as if you were inside the box (which explains why in 3rd angle the right side view is on the right side of the front and why it is on the left side of the front view in 1st angle is on the right). To this day that is how I explain this to my students.

 

[peterl95124]

Dieter,
yes, perfectly clear now, many thanks for the language translation !!!
Peter

(the only german I know is "das machined ist nitch for der fingerpoken und der mittengrabben, ..." !!!)

Hi Peter

we are talking about this section of the picture.

View attachment 153301

Here I make the translation from the German text:

Application:
If important things are to be shown in the front view.
Dimensions in directions A and B = scale size.
Towards C = 1/2 scale size

For your example:
Direction to A (7°) = 100% of dimension (200 mm = 200 mm in drawing)
Direction to B (90°) = 100% of dimension (100 mm = 100 mm in drawing)
Direction to C (42°) = 50% of dimension (100 mm = 50 mm in drawing)

I hope, it is clear described?
If you have any further question, please do not hesitate to aks.

Regards
Dieter

 

[bluejets]

Here is a simple example of why knowing the projection used is helpful. With no hidden detail which side are these blind holes drilled in?

Doesn't make a scrap of difference.
Rotate part 180 degrees, same same.

 

[HMEL]

Here is a simple example of why knowing the projection used is helpful. With no hidden detail which side are these blind holes drilled in?

View attachment 153264

So missing are the hidden lines put them in and you know.

 

[HMEL]

I have tried to research where the first angle and third angle view terms were initiated or used. None of the older drawing books use these terms so I suspect they are a result of modern cad techniques because until recently it was difficult to work at different angles. In fact I find the top, front and side view to be more specific and easily understood drawing terms. I have also seen with cad the omitting of hidden lines which are important tools in clarifying the drawing. I think its one of those issues that attempts to make drawings more complicated then they need to be. I only find these terms in academic papers trying to explain simple concepts to make the paper more scholarly appearing. Complex angles occur quite often in sheet metal drawings and require far more care then a 1st angle or third angle because they can occur on a plane which could be any angle. These were done long before cad was available.

So if anyone knows where these terms originated or who started them I would appreciate just knowing how they came about and when?

 

[petertha]

Solidworks allows you to drop a part on the sheet, and depending on how it lands, then you can pull a projected view left, right, up, down, or at any one of four 45 degree angles for isometrics.

If you don't get exactly what you want, you can project off of the side of a projected view, but I seldom use that feature.

So I always use top, bottom, left, right, and one or more osometrics, and label each view as such.
Perhaps that is why some drawings confuse me; they don't have the left,right,bottom,top labels.

Yes, you are familiar with dropping the part & pulling the various projected views in the drawing. But maybe what you don't realize is what's happening behind the scenes. SW is obeying the setting (First or Third) presently defined in your drawing sheet properties. If you toggled from one to another it is smart enough to draw the views correctly according to the standard. Nothing for you to think about or correct for since the model itself has not changed. You can save whatever setting to a template so it does it every time, or you can override it, or you van have a template for each, or..... I think the drawing symbol can be displayed (maybe you have it turned off) and/or can otherwise be auto-listed on the drawing as a property, just like mass or scale etc.

As mentioned, avoid mixing modes together on a drawing set & particularly on the same drawing to avoid confusion.
Top,Bot,Right... I think fell out of favor a long time ago, maybe as computer modelers came along. It only makes sense by further defining from whose perspective & that can vary significantly.
Your F1 key (help) should bring up something like this or just Google it

https://help.solidworks.com/2020/English/SolidWorks/sldworks/c_projected_view.htm

 

[GreenTwin]

Thanks Petertha, I will have to play around with that in Solidworks.

Thanks to all who are contributing information here.

Most interesting topic for sure.

I have a drafting book I used in school, dating back to perhaps the early 1980's, so I will dig that out and see if I just skipped over that section, or what.

When I started in engineering school, drafting courses were mandatory.
They had huge rooms full of drafting tables.

When I started working, we all had drafting tables, with parallel bars.
The parallel bars worked very well, and were a definite improvement over the T-bars or whatever those were called.
I never liked those moveable arm contraptions.

We stood all day and hand drew everything, pencil and ink on vellum (modern vellum).
The drawings were generally 30" tall and 42" long.

These days, most seem to have standardized on 24" x 36" drawings, which are much easier to physically handle.

And with pdf files, we seldom plot anything anymore, which is good, because plotters can be difficult and expensive to maintain.

When CAD programs came along, the folks who did the CAD work were more computer types, and not traditional draftspeople, so they used all the same linetype for every line. The drawings looked terrible, with no contrast at all.

.

 

[JohnBDownunder]

Green twin, here in Australia we went metric 1966 I think? Memory fails in stuff it seems to deem unimportant but weirdly whilst I use metric my grey matter will look at 75mm and tell me "About 3 inches". Similarly with 150mm 6" 300 foot. This I think just gives me a mental image of stuff.

 

[GreenTwin]

Green twin, here in Australia we went metric 1966 I think? Memory fails in stuff it seems to deem unimportant but weirdly whilst I use metric my grey matter will look at 75mm and tell me "About 3 inches". Similarly with 150mm 6" 300 foot. This I think just gives me a mental image of stuff.

I have asked people in the metric world how they can envision things without the unit "feet", ie: that telephone pole is 40 feet tall, or that tank is 30 feet in diameter.

The response is that they can indeed envision the approximate size of things using mm, or I guess meters, etc.
Such would have to be the case, else it would be very difficult to build large physical structures.

I wish I could look at something like a 4x8 sheet of plywood and immediately think in terms of mm or some other metric unit, but I can't, and I don't know anyone else in the building industry who can (I know a lot of folks in the construction industry here).

I am not sure how we get acceptance of the metric system here without overcoming the groupthink here of inches/feet/yards.

There is a lot of dual labeling these days, and I notice it a lot on wood products, but generally they break down something with nice round imperial units such as a 4x8 sheet of plywood to a very cumbersome 1219.2 mm x 2438.4 mm.

This is the issue that must be overcome.
Every structure in this country (homes, factories, truck trailers, etc.) are built in nice round units of inches/feet/yards.

For equipment assemblies, automobiles, etc. the metric seems to go better.
For large construction, the metric does on work so well.

I am not against metric by any stretch, but there are some very rational/practical reasons why it has not been widely accepted here in many applications.

Edit:
On project sites, I often step off distances, with each step being approximately 12".
Very useful for getting approximate distances quickly.
Does this happen with metric?

Edit2:
I think the unit of feet can from the human foot ? and the yard came from the length of the human arm ?
So easy to envision.
Not sure where inches came from.

Metric would be much easier if it had the unit "foot-o-meter".
Is it too late to add that unit to the metric system?
If that unit gets added, remember you heard it here first.


.

 

[Jasonb]

Flipping that part 180 deg won't work as the holes are not exactly symmetrical about the mid point.

While hidden detail can help there are some instances where it can clutter a drawing so sometimes better to add a second view so you have one of both, dimension the visible external detail on the one without and any of the hidden detail dimensioned on the other.

Pat you need to ask someone in Europe who has never used feet and inches how they think as it will be in metric. Asking a bunch of old guys who were brought up with imperial won't be the same. I have a client who is French but lived in the UK for 25+ years. Whenever I talk to her in metric she gets a rule or tape out so she can then visualise it in cm so I just talk metric with her now.

We have the fun fact that ply is sold as 1220 x 2440 but joists & studs are spaced at 400mm ctrs not the metric conversion of 16" so joints don't line up. plasterboard though is 1200mm wide.