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Sat

Is this a first angle or third angle projection?

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Sat

I found this image in a textbook and it's supposed to be a three view first angle projection of the boat. It looks like main view is a plan view (top).

 

What confuses me about this is that the left view, looks like it's of the left side. But only third angle projections order views this way (left view being of the left side, top view being of the top, right view being of the right). So is this picture a first angle projection or a third angle? Or is it all together wrong?

 

9ay3av.jpg

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Stryker1989

from experience I would say you are right in thinking it's third angle (left on the left, top on top etc.) is there no projection symbol on the original drawing?

 

EDIT: Just had another look and I think it may be right in saying it's 1st angle as the view is projected to the plane in that if you looked at it from the right you would see what is drawn on the left.

 

hope that isn't too confusing.

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rkent

It is First angle. Third angle projection can include a left view so that is not the definition of First or Third angle projection.

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Patrick Hughes

I've got to disagree rkent - that is third angle projection.

 

Something I've found to be useful to differentiate the two is if you mentally place an object in an imaginary bowl as you slide the object up the wall of the bowl that will produce a third angle view. Now if you invert the bowl and place the object on top, as you slide the object down the bowl wall it produces a first angle view.

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rkent

It is a right side view placed on the left side, smells like First Angle to me.

 

There are two lines that I would have expected to be hidden lines, not sure if the image is not showing those properly or the drawing was done poorly.

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Patrick Hughes

Well the OP actually had it right - it is altogether wrong.

 

The left side view does appear to be the right side view placed on the left. That in itself does not make it a first angle view. If it were a first angle view the "plate" portion of the object would be nearer the plan view (use my bowl visualization). Also look at the partial front view - that is third angle.

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Stryker1989

I agree with both of you. It looks like it may be First Angle, but it is First Angle drawn incorrectly for the reason Patrick gives.

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JD Mather

Why doesn't someone simply model the part using a modern MCAD program like Autodesk Inventor to create both 3rd angle and 1st angle projections to verify? :o

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SLW210
Why doesn't someone simply model the part using a modern MCAD program like Autodesk Inventor to create both 3rd angle and 1st angle projections to verify? :o

 

Post an image. I cannot view whatever is in the OPs post.

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JD Mather

The drawing is not correct for 1st angle or 3rd angle.

 

Here is 1st angle and 3rd angle solutions (taken from given view).

Projection.png

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Ryder76

Maybe this is a better explanation.

 

1. First angle projection and Third angle projection are two different conventions used in drawing the orthographic projections of a 3-D object. First angle projection is like keeping a solid in front of a screen and seeing it from the other side of the screen. It is just projecting all the edges , points features etc.. over a plane that is behind the solid.

 

Third angle projection is just seeing and drawing the views in the respective sides.. that is in 3rd angle projection, front view is in normal position, top view in top, left side view on left and right side view on right. Whereas in first angle projection, top view is at the bottom, left side view on the right and right side view on the left.

 

2. U can distinguish between first angle projection and third angle projection by seeing the representation in the Title block. If it shows a trapezium followed by a concentric circles, then it is first angle projection. If the circles precede the trapezium, then it is third angle projection.( it represents the views of a truncated cone )

 

3. Only in many educational institutions they are following first angle projection. In many industries they still use third angle projection. But they won't use second angle and fourth angle projection because the views get merged and leads to ambiguity.

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Jack_O'neill

If you do lots of mechanical drawing (which in my case has always been done in third angle), first angle projection always seems backwards, at least to me. If you have a top view, it's placed below the front view, yet it shows the top. A right side view is pulled off to the left of the front view, and so forth.

 

Third angle makes more sense to me. If you are looking at the front view, the right side view is on the right side. Left side view is on the left side, top view is above the front and so forth. Its as if the object is stationary, and you are moving around it. If you want to see the right side of the object, step around it to the right and that's what you see.

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nestly

How ironic that the PDF in post #10 says;

 

"Ensure that a drawing and or drawing package is in the standard projection format as mislabeling the drawing as third angle in the title block and putting the part in first angle can lead to a misunderstanding and or confusion on design intent."

 

.... and then they use the 3rd angle symbol in the title block for both the 1st and 3rd angle drawings.

 

Personally, I've never payed a bit of attention to 1st angle, 3rd angle, or 27th angle . Neither the inclusion, or omission of that symbol, nor the orientation of the views have any bearing on whether an otherwise properly drawn part will be read correctly.

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Ryder76
How ironic that the PDF in post #10 says;

 

"Ensure that a drawing and or drawing package is in the standard projection format as mislabeling the drawing as third angle in the title block and putting the part in first angle can lead to a misunderstanding and or confusion on design intent."

 

.... and then they use the 3rd angle symbol in the title block for both the 1st and 3rd angle drawings.

 

 

Right!?!?!?:facepalm:

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Patrick Hughes
Why doesn't someone simply model the part using a modern MCAD program like Autodesk Inventor to create both 3rd angle and 1st angle projections to verify? :o

 

Why do you need a modern program? :twisted: This was done in r14:

 

Projection.jpg

Edited by Patrick Hughes
Oh Snap. I didn't see your image.

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nestly
Why do you need a modern program?

 

I'm guessing the phrase "modern CAD program" is copyrighted and a royalty check gets cut every time it appears in a post. :P

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rkent
I'm guessing the phrase "modern CAD program" is copyrighted and a royalty check gets cut every time it appears in a post. :P

 

I think he is paid in Smug Dollars.

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Sat

Sh*t, a lot of comments...I'll read them through in a bit. As for people wondering why it has no explanation etc; it's from an exercise book and you're meant to figure some details out for yourself.

 

Edit:

Ok, read through the comments, thanks for the replies. Honestly, I'm still a bit confused. I think I understand first and third angle fairly well by now. So my conclusion is still that the drawing is incorrect.

 

JD Mather: Thanks for the illustration, yes, the first angle view you did is how I thought it should've been done in the original drawing too, so if they had done it like you did it I would've understood it.

Edited by Sat
Read through the posts

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rkent
Why do you need a modern program? :twisted: This was done in r14:

 

[ATTACH=CONFIG]30116[/ATTACH]

 

Patrick,

Very nice illustration, makes things easy.

 

rkent

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