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

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

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

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

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

God, I envy you. Here in the US, we're still not sure if this CAD stuff is gonna 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

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 gotta love Banff - that is world class spectacular!

Danger

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

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.