Drawing Projections

[Michael GilliganParticipant @michaelgilligan61133]

Jason,

This does seem to have got rather out of hand, doesn't it.

My second note to Wolfie last night was a genuine question.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dave Morris 1 on 17/09/2012 23:22:27:

just found this **LINK**

Dave,

That video is brilliant

Thank You

MichaelG.

[jason udallParticipant @jasonudall57142]

Posted by Michael Gilligan on 18/09/2012 10:50:26:

Posted by Dave Morris 1 on 17/09/2012 23:22:27:

just found this **LINK**

Dave,

That video is brilliant

Thank You

MichaelG.

Ditto I had planned to post that same l;ink.. . best most graphic "mnemonic" I have seen…GUYs ( and gals) you realy should bother to watch that one… not least for the " model" subject…

[WolfieParticipant @wolfie]

So the only difference between 1st and 3rd angle is that the various views are in different positions relative to the 'front' view.

How silly is that?? Its the same diagram, just rearranged. No wonder its confusing cos as a novice you are looking for something much more complicated.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Wolfie on 19/09/2012 08:45:45:

So the only difference between 1st and 3rd angle is that the various views are in different positions relative to the 'front' view.

How silly is that?? Its the same diagram, just rearranged. No wonder its confusing cos as a novice you are looking for something much more complicated.

 

Yes

… It's rather like driving on the Left or the Right side of the road.

… Two choices, each equally valid

But it does sometimes help to know which convention has been adopted.

MichaelG.

 

P.S. There is a remarkably thorough page on Wikipedia.

Edited By Michael Gilligan on 19/09/2012 08:58:38

[VersabossParticipant @versaboss]

The all important words 'position / positioning' were mentioned first by TerryD (17.9./13:24), then by Keith Long (17.9./15:01), then Michael Gilligan (17.9./19:34).

Words with similar meaning (e,g, Stub Mandrel: arranged) even much earlier.

Sometimes it needs a long time to sink the simplest things into our brains,

Greetings, Hansrudolf

Edited By Versaboss on 19/09/2012 11:59:48

(name correction)

Edited By Versaboss on 19/09/2012 12:00:48

[Sub MandrelParticipant @submandrel]

Wolfie,

You question the value of knowing the projection. This example shows a front bview and two side views of a part:

If you don't know whether this is first or third angle, you can't tell which of two possible shapes the object is.

Now think of something complex like a real car engine block, or a house… actually the simpler the part, the greater the chances of an error.

Neil

Edited By Stub Mandrel on 19/09/2012 21:04:25

[jason udallParticipant @jasonudall57142]

Welll….looks like view on left of main view is wrong…but the point is correct….A knoledge of the system in use is as much a part of the drawing as any view.

 

Now try and complete the side view of the following

 

 

Edited By jason udall on 19/09/2012 23:37:49

[TerrydParticipant @terryd72465]

"How silly is that?? Its the same diagram, just rearranged. No wonder its confusing cos as a novice you are looking for something much more complicated."

Hi Wolfie,

Here is a drawing of a simple component.  Projection method (1st or 3rd) is not specified. Does it matter?  Draw me a 3D sketch and post it here.

 

 

Best regards

Terry

Edited By Terryd on 20/09/2012 07:12:42

[TerrydParticipant @terryd72465]

Posted by jason udall on 19/09/2012 23:24:36:

Welll….looks like view on left of main view is wrong…but the point is correct….A knoledge of the system in use is as much a part of the drawing as any view.

 

Now try and complete the side view of the following

 

 

Edited By jason udall on 19/09/2012 23:37:49

Hi Jason,

This has been covered in a another thread some time ago

 

The first 4 possible solutions are third angle while the last is in 1st angle.

There are actually an infinite number of theoretical siolutions as the sloping face could be a curve and the central element can be either a cut out or a projection from the surfave and could be of almost any profile especially if hidden lines are excluded.

Interesting, classic example.

Best regards

Terry

Edited By Terryd on 20/09/2012 08:23:51

[jason udallParticipant @jasonudall57142]

Terry.. Classic to us..new to others .. but yes .met it myself when 11….still stays with me today.

we had to also develope and build solid model ( back when that ment card knife and glue)

[WolfieParticipant @wolfie]

These problems are interesting but they are asking for the side view and not where to place it so are immaterial to the original question.

I have to say that I would have thought it was blindingly obvious to put the left hand side projection on the left, and the right hand side on the right, the top at the top and so on. Who would do it any other way???

"Hi Wolfie,

Here is a drawing of a simple component. Projection method (1st or 3rd) is not specified. Does it matter? Draw me a 3D sketch and post it here."

OK no doubt I have fallen for some trick here  but here goes, being as you haven't included the top view I appreciate thet the rear may be different to the front  (not to scale)….

 

 

Edited By Wolfie on 20/09/2012 12:36:23

[TerrydParticipant @terryd72465]

Qute:- "These problems are interesting but they are asking for the side view and not where to place it so are immaterial to the original question.

I have to say that I would have thought it was blindingly obvious to put the left hand side projection on the left, and the right hand side on the right, the top at the top and so on. Who would do it any other way??"

 

Hi Wolfie,

Firstly they are very relevant and your second statement seems to suggest that you have not understood that relevance, it is not simply about how views are located, it is about how they are placed relative to a hypothetical viewer of the component being drawn.  It is that which can lead to confusion between the two systems.

Your drawing is close, but not close enough. Notice the vertical lines on the elevations (solid and dashed) that should give you more of a clue, every line in an engineering drawing is important and ignored at ones peril. A person who can read engineering drawings does not really need a plan view here as it would not reveal any extra detail. and there is nothing that my drawings do not show, except the projection system (and of course dimensions), which is crucial to its accurate interpretation.  If extra detail is needed I would have drawn the plan view.

My Chief draftsman always insisted on economy as he viewed unnecessary drawing as a waste of time. As that great pioneering engineer Henry Maudslay said –

"Avoid complexities. Make everything as simple as possible." and

"Get rid of every pound of material you can do without; put to yourself the question, ‘What business has this to be there?"

A few designers in the pages of ME and MEW could do no better than to have this advice pinned over their workbenches.

By the way I will post a 3D sketch when you have had time to consider the above.

Best Regards

Terry

Edited By Terryd on 20/09/2012 13:16:12

[WolfieParticipant @wolfie]

OK lets try this then (Ignore the lack of drawing skills lol )

Edited By Wolfie on 20/09/2012 13:31:26

[TerrydParticipant @terryd72465]

Hi Wolfie,

Better, and half right. (drawing skills no problem, as long as you can put over an idea accurately it is inconsequential). Actually that is one possibility, however if you gave that to an engineer he would either wonder what the line down the centre of the top represents or conclude that it is two seperate components.

These are the two possible solutions (there are others but more of that later) :-

If the drawing was in first angle proj. it would look like the example on the left (as you drew it, but rotated 180) the sketch on the right is what the component would look like in 3rd angle. Of course this is a simple example and would be explained with a plan view, but not all confusions are this simple and can lead to some real problems if the conventions are not understood and observed.

The cut out could also be curved (e.g. quadrant) and that would also need a plan. I have though seen drawings in ME which have confused me until I realised that one side view was in first angle projection and the other in third angle . It is useful to understand the differences and be able to interpret drawings correctly to prevent expensive errors

I was recently able to buy for pennies a rather nice piece of steel, about 20mm thick by 300mm wide and 450 mm long which had been accurately ground on both sides. The unfortunate machine operator had read the drawings wrongly (1st/3rd angle confusion) and made a very expensive piece of scrap – great for me, not so for him I believe.

It's not just a pedantic exercise, believe me, when some use 1st angle and others 3rd angle projection systems. It would be good if we could all agree on one system but its a bit like the metric v imperial debate, but let's not go there – its Tiger country!

Best regards

Terry

Edited By Terryd on 20/09/2012 14:27:57

[WolfieParticipant @wolfie]

"Actually that is one possibility, however if you gave that to an engineer he would either wonder what the line down the centre of the top represents or conclude that it is two seperate components."

The line is down the middle cos I couldn't work out how to rub just half of it out lol

Edited By Wolfie on 20/09/2012 17:29:00

[WolfieParticipant @wolfie]

Actually I've just noticed summat. If you rotate those two solids 180º they swap projections. I drew your left hand one but I thought it was 3rd angle cos the end view was on the right.

[nigel jones 5Participant @nigeljones5]

Now im convinced thats not right….have a look at this http://www.youtube.com/watch?v=_wDpN6Zi1hE

[Ed DuffnerParticipant @edduffner79357]

I've wondered about these projections myself and to be honest can't see the point of having or using them. If a drawing is made clear enough with enough views of the part, why introduce a layer of confusion.

The examples of the square inside another where you have to show the side view would never come up in real life surely? it would be an incomplete drawing yes?

It's the same with off-side and near-side on a car, what happened to left and right?

[blowlampParticipant @blowlamp]

Posted by Ed Duffner on 26/11/2012 12:40:33:

I've wondered about these projections myself and to be honest can't see the point of having or using them. If a drawing is made clear enough with enough views of the part, why introduce a layer of confusion.

The examples of the square inside another where you have to show the side view would never come up in real life surely? it would be an incomplete drawing yes?

It's the same with off-side and near-side on a car, what happened to left and right?

Left and right change, depending on if you're looking from the front or the rear.

Martin.

[Gordon WParticipant @gordonw]

Or ,of course left and right hand drive.

[Mark CParticipant @markc]

I thought I might add a bit to this – I have read the whole thread (but not all the links) and cannot find any mention to the link between CAD and 3rd angle.

CAD is generally drawn 3rd angle (and I think there is mention of it being preferred in the old BS308) today unless there is a specific reason (locally) to do otherwise. It is done mainly due to a desire to make drawings un-ambiguous as has been stated before – disambiguation is the key to preventing scrap parts and wasted time/money along with recrimination about "who was to fault". As the parts get more complex, the greater the importance of the drawing layout – I have attached a drawing for a part that I drew to give an idea of how a modern CAD drawn part would be produced. It is not complete in the sense that there are a number of extra "sheets" to fully detail it along with a file containing the 3D solid geometry for direct import into the machine center (saved as "as cast" geometry including shrinkage and machining allowances). You will notice the projection information (little cone) and the magic words "if in doubt, ask" which roughley translate to "on your bike, I am making it like this!"

Mark

[hawkeyefxrParticipant @hawkeyefxr]

When i was doing my apprieticship in the 60's i had a spell in the drawing office, i was told one was the American view the other English view, Which was what i can't remeber now.

[Alan JacksonParticipant @alanjackson47790]

Posted by hawkeyefxr on 17/05/2013 06:31:07:

When i was doing my apprieticship in the 60's i had a spell in the drawing office, i was told one was the American view the other English view, Which was what i can't remeber now.

I think 3rd angle projection is american and mostly used. If you ever got a ist angle (english) drawing it became misleading and you had to read it with care to avoid misinterpretation. The comment "If in doubt ask" was often cynically restated " If in doubt don't ask" you got no help from nobody.

Alan

[M0BNDParticipant @m0bnd]

I see a lot of German drawings – all 1st angle! They can catch you out because your eyes and brain get used to 3rd and the drawings look very weird.

I haven't followed or read all the posts on this thread but I was always taught 1st angle is to take the part and just roll it to the new view(to the left, right, top or bottom). For 3rd angle, pick up and place to the left, right, top or bottom. Hope this helps!

[Author]

Posts