First angle,third angle projection

[chandran]

can anyone explain
1)first angle projection
2)third angle projection

what are the advantages & disadvantages of the above

why not use second and fourth angle.

 

[FredGarvin]

It all boils down to what one wants to call the "front" and "side" views of an object. The only difference between them is how the views are laid out on the print. First angle is used mostly in Europe. I am used to the third angle projection myself. It doesn't really effect the outcome, just how it looks in presentation, so there are no real advantages or disadvantages to be had. The same part will have the same views, just laid out a bit differently. It doesn't take long before you don't even realize what projection one is looking at. You're just looking at a print.

Take a look here for a good example showing the same part in both projections:
http://www.technologystudent.com/designpro/ortho1.htm

Honestly, I have NEVER wondered about the 2nd angle...hmmm...maybe I should think of more questions like this myself.

 

[Stokes Al]

Test

 

[Stokes Al]

I disagree with the statement that there are no real advantages or disadvantages to using first angle or third angle projection. Third angle projection is simpler to use than first angle projection for the reasons given below.

In engineering college I used the first angle projection for several years. Immediately after graduation, I came to the United States and had to use third angle projection exclusively.

Pretend that the object to be drawn is inside an opaque box in the first angle projection and inside a transparent box in the third angle projection.

In the first angle projection, you have to go inside the opaque box to draw the object. What is seen, you project and draw onto the wall at the rear of the object. It is like putting the object between you and the blackboard. What is seen, you project and draw onto the blackboard. Finally, to get the six views, the box is cut flat as you like.

On the other hand, in the third angle projection, you stay outside the transparent box to draw the object. You draw what you see on the transparent box. (In computer jargon:
WYSIWYG - What You See Is What You Get). It is like putting the object to be drawn behind a tracing glass table. You simply draw what you see. Finally, to get the six views, the box is cut flat as you like.

Second and fourth angle projection would be a hybrid of the above two. It would require a box with three faces opaque and three faces transparent. This would be confusing and disadvantageous.

As they say, think outside the box!

 

[FredGarvin]

Your argument makes no sense. In both projections, you draw what you see. There is no difference except in the mental method one uses. If you took two different prints using the two projections, the views would be identical, just laid out differently. If one way works better for you. Great. That's your opinion and it gets the job done. When you've done a couple thousand prints, you won't even think about what you're doing.

BTW, I don't think the OP will notice your response since this thread is almost two years old.

 

[TVP45]

Your argument makes no sense. In both projections, you draw what you see. There is no difference except in the mental method one uses. If you took two different prints using the two projections, the views would be identical, just laid out differently. If one way works better for you. Great. That's your opinion and it gets the job done. When you've done a couple thousand prints, you won't even think about what you're doing.

BTW, I don't think the OP will notice your response since this thread is almost two years old.

I've worked with both quite a bit over the years. There's no difference that I can see. I just got into the habit of looking down at the title block to see which way that drawing is projected. And, of course, once I went to SolidWorks, the difference was merely a radio button setting.

 

[Danger]

This is kinda strange; I've never heard of any 'angles'. Going by the examples in Fred's link, the method that I use must be 'first angle', except that my top view (what you call 'plan') is directly above the front view rather than below the side one. That's the way that I was taught in my 2 years of high-school draughting class.

 

[TVP45]

Nah, you're Canadian. You should be using third angle; at least that's what the guys I used to work with in Calgary used. It's most noticeable in the right side view. Look at your wrist watch straight on and call that the front view. The side view where you see the winder knob is the right view in third angle; it's the left view in first angle.

 

[brewnog]

I use both, but generally third angle. Makes no difference to me. It doesn't matter which you use; the important thing is that you're clear on your drawing which method is being used so that the guy making it knows what's going on.

I don't understand what Stokes Al is getting at though.

 

[Danger]

The side view where you see the winder knob is the right view in third angle; it's the left view in first angle.

That didn't help a bit; my watch doesn't have a winder knob.
By your watch example, I would have my top view, which is looking directly at the face. Straight below that would be the front view, as if you were standing on the wristband. To the right of that would be the side view (right), which would be looking directly at the winder knob if it had one.
Incidentally, I'm very close to Calgary, but learned draughting in Ontario.

 

[mgb_phys]

I had completely forgotten all the confusion that used to cause between the UK/USA - now 3d cad just makes everything much easier. We don't even make paper drawings anymore, the 3dmodel just goes straight to the machine shop and into the CNC machines.

 

[TVP45]

That didn't help a bit; my watch doesn't have a winder knob.
By your watch example, I would have my top view, which is looking directly at the face. Straight below that would be the front view, as if you were standing on the wristband. To the right of that would be the side view (right), which would be looking directly at the winder knob if it had one.
Incidentally, I'm very close to Calgary, but learned draughting in Ontario.

Well, heck, I couldn't think of anything else real fast. No knob, huh? What won't they think of next. So, if we use your car and you see the grille in the front view, the driver's door is in the right view in 3rd angle projection. In 1st angle projection, the driver's door would be in the left view.

Beautiful country up there around Calgary. And, only three more months till spring...

 

[Danger]

only three more months till spring...

Unfortunately, that means only four more months until winter.

Okay, I guess that I use 3rd angle. Still, my placement seems to be different.

 

[TVP45]

I had completely forgotten all the confusion that used to cause between the UK/USA - now 3d cad just makes everything much easier. We don't even make paper drawings anymore, the 3dmodel just goes straight to the machine shop and into the CNC machines.

God, I envy you. Here in the US, we're still not sure if this CAD stuff is going to catch on. In my last full-time job, I made 3D models, which the machine shop needed in order to make the parts. But, because of our QA/QC standards, I had to turn the 3D model into a 2D drawing, specifically an AutoCad drawing, and then add the 3D model file location in the reference block of the drawing title. The 2D drawing went to the machinist who, because he couldn't use the 2D drawing, would read the name of the 3D file he really needed, then call us up and ask for it. Then we'd send that to him on a CD since we didn't believe in file transfer protocols. Oy vey!

 

[TVP45]

Unfortunately, that means only four more months until winter.

Okay, I guess that I use 3rd angle. Still, my placement seems to be different.

Yeah, it startled me to come up to Calgary and see all the snow on the mountains. I innocently asked, when do you get the first snow here and was told, "August". I think it came early that year, but still the sight of all those outlets for block heaters told me a lot. Still, you got to love Banff - that is world class spectacular!

 

[Danger]

you got to love Banff - that is world class spectacular!

Yeah, and world-class expensive. The cost of living there is unbelievable. Still, it certainly is a gorgeous location.

edit: By the bye, it's bloody snowing here again.

 

[mgb_phys]

God, I envy you. Here in the US, we're still not sure if this CAD stuff is going to catch on. ... Oy vey!

Our first NC machine was like that - you had to redraw the part in 2d on the mickey mouse cad system on the PC that was running the machine, make a mistake and it would happily run the cutter through the bed.

Then we got HAAS machines that just take the cad model - amazing to watch them.

 

[TVP45]

Yeah, and world-class expensive. The cost of living there is unbelievable. Still, it certainly is a gorgeous location.

edit: By the bye, it's bloody snowing here again.

That's OK. A hillbilly like me couldn't live there anyway. I didn't see any house trailers, no rusty cars up on cinder blocks in the front yards, and nobody appeared to have a gun rack in their pickup. You're nice people up there, but you just don't seem to have nearly enough bad habits.

 

[TVP45]

Our first NC machine was like that - you had to redraw the part in 2d on the mickey mouse cad system on the PC that was running the machine, make a mistake and it would happily run the cutter through the bed.

Then we got HAAS machines that just take the cad model - amazing to watch them.

Yeah, a couple years ago I worked with a plastic fabricator out in Indianapolis who refused to even look at a paper drawing. It was 3D or nothing. He did beautiful work and it was so easy to work with him.

 

[Danger]

you just don't seem to have nearly enough bad habits.

We have plenty, but we try to keep them to ourselves.

 

[FredGarvin]

I wish sometimes that we could move entirely to the math based machining type of platforms. I do conceptual cross sections for design reviews and then move on to full modeling and drawings to the T on every part. It is time consuming, but boy, you sure know a design when you're done.

 

[MJK289]

Base View

The side view where you see the winder knob is the right view in third angle; it's the left view in first angle.

If you don't mind I'd like to clarify your otherwise great explanation. The right view is still the right view but on the left side of the front view. Now my question is if the base view is the same by convention. In third angle the base view is the front view. However, I've been seeing a lot first angle drawings with the side view as the base view. For example, the top view is placed under the side view instead of under the front view.

 

[MJK289]

The other thing that I'm not sure about between the two conventions is if the Isometric view is the same. Sometimes I see the 3d view shown from a different corner of the cube so that the front is where the right view would usually be. I'm not sure if this is just a preference of the designer or if the convention is different for Ansi and Iso with respect to the standard southeast isometric view. I think this ties in with what you define as the base view, which I'm trying to determine.

 

[TVP45]

The isometric view will be the same. It is a normally a projection off the front view and, so, reflects any side specific features that you would see as hidden lines in the front view. I often use a 3D view that is far enough off that it is clear it is not isometric and then I place it someplace where it is again clear that this is not an isometric. I'm not sure what you mean by a SE isometric view, but you usually want to show the same three views you've drawn in 2D.

The front view (the base view) will be the same in either system and is selected from all the possible views based on its importance, i.e., number of features, criticality of features, etc.

The number of other views is based on the criteria that you always make the minimum number of views required to accurately and easily manufacture the part/assy. Often this will be driven by dimensioning needs. There is nothing magic about three views except that this is a de facto standard. I'm currently working on motor control assemblies that have twelve or more views.

In ANSI the right side view will be placed to the right of the front view. The top view will be placed above the front view.

In ISO, the left side view will be placed to the right of the front view. The top view will be placed below the front view.

Again, the overarching criteria is clarity. If there is any possible way to misinterpret your view placement, that needs to be corrected. Unless you have an anal customer who absolutely insists on certain standards, choose the views that guarantee accuracy. As to first angle or third angle, make sure your title block has the standard symbol for your projection type.

 

[MJK289]

Thanks TVP45. Isometric views are clear to me now. It should have been obvious to me. Anyway, Southeast Isometric view is AutoCAD terminology for a view from the front right which on a drawing would be located at the top right of the drawing sheet. (in 3rd angle projection) I never thought of it as a projection off the base view. Now I see that in a three view drawing you place the projected isometric in the empty corner of the drawing. I played around with my 3d program trying this and it came out correctly depicting the three views I drew. I was just stuck on the fact that up until now I always saw it on the top right of the sheet. My drawings too are more complicated than this and all in 2d and mostly without any isometric views, but I'm now modeling everything previously drawn in AutoCAD with a parametric program and showing 3d views.
My drawings are correct, however, I got to thinking how I want to do things so I can be consistent when possible.
This post stems from the fact that I usually draw the right view but the left was more important and I only wanted to look from one side. Of course this is not a problem, however, since this is my design I could mirror my plan and thus have the right view as the important one. But, I'm sticking with the Front, Left, and Plan view. Since I'm working in First angle I got to thinkng about how the Europeans draw. For European drawings I already changed the way I do section lines and I place the view label on top instead of under the view. Anyway, what i came here to find out was if, when all views are of equal importance, do Europeans also prefer to draw the right view instead of the left? I'm assuming for simple drawings everyone agrees that in USA its the right view that is usually drawn. Same in Europe? I noticed, TVP45, you described the left view when you explained first angle instead of saying the right view is place on the left side.
I hope I don't sound completely anal. Thanks again.

 

[TVP45]

I don't have enough experience with European drawing practices to say anything about their preferences. About 90% of the drawings I've worked with came out of the European Space Agency and would reflect their standards I suspect.

In the US, the default is the right view but only for simple drawings, as in catalogs or textbooks. Overall, the preference is always for the minimum number of views required to clearly and accurately show the part/assembly. I have done drawings in which all the views were auxilliary views except for the one view which showed the orientation of those auxilliary views.

I may have confused you when I said left view or right view. I have not used view labels for many decades and may be using them carelessly. In my experience, views are typically either very obvious (and no label is required), or the front view only is labeled, or labels such as "View A" are used.

 

[rdt2]

http://en.wikipedia.org/wiki/Orthographic_projection

explains the how and why of the projection systems. The 'truncated cone' universal symbol illustrates the difference and the link to Limerick Uni's site is useful. Neither 1st nor 3rd angle is intrinsically superior. UK practice varies from company to company: 1st angle was 'traditionally' used but there's a trend towards 3rd angle.

 

[john walsh]

can anyone explain
1)first angle projection
2)third angle projection

what are the advantages & disadvantages of the above

why not use second and fourth angle.

First and third angle projection have been defined very nicely by other members.
The usual reason for choosing one or the other is because most people in your region/school/environment use it.
For that reason, I used to use first angle projection but I changed to third angle for the following reason:
If you study a drawing of a large object with lots of detail on all faces, if first angle projection is used, to view the details on the right hand side of the principal view you must look to your left. It can be difficult to relate an object in one view to that object in the other view because the are very far apart.
I third angle projection, objects on the right hand side of the principal view are projected to the right and kept close.
Furthermore, if you study an object inyour hands, to study the right hand side you naturally turn that side to the front.

I assume the second angle is the rear view and fourth angle is the front fiew.

 

[DrMik]

Yup. I was taught first angle in school 'technical drawing class', but was told of 3rd. When working as an engineer all the drawings of the stuff I made came in 3rd angle *(both European and US). I thought this blog deserved noting in the 22nd decade.