Drawing Projections

[David JuppParticipant @davidjupp51506]

The 3D CAD system that I use assumes by default 3rd angle for inch based templates (US paper sizes), and 1st angle for Metric (ISO paper sizes). This is simply down to the way the provided 2D templates are set up.

This can catch out the unwary, especially as the projection method can only simply be changed before adding views to the drawing.

For this (and some other reasons of style/preference) I recommend that users set up their own drawing templates, customised to give their desired 'look' to their drawings.

[Ady1Participant @ady1]

Maybe this is why so many government development projects went miles overbudget

in the case of Concorde Denis Healy said "Eventually we simply stopped counting how much it cost"

[thomas oliver 2Participant @thomasoliver2]

Putting it all as simply as possible:-

1st Angle Looking at the front elevation – What is seen from the left is projected over on the right.

What is seen from the right is projected on the left.

What is seen from above is projected below.

3rd Angle Looking at the front elevation- What is seen from the left is projected on the left.

What is seen from the right is projectied on the riight.

What is seen from above is projected above.

The spacing of views on the paper is first worked out and normally the FE is drawn, then one side elevation. By projection lines directly from these views, and via a 45 degree line, the plan view can be drawn without measurement.

[Russ BParticipant @russb]

Posted by Wolfie on 20/09/2012 12:34:04:

 

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???

 

3rd angle is only used America and Australia, the rest of the world uses 1st angle ortho – so not really that obvious, and not "as previously used in the UK" either – it really depends on your way of thinking.

The easiest way to understand the difference is by imagining that your "object" never leaves the page, – now this is a fairly lose analagy from my brain – for a proper insight, as I think previously linked see here – but you might get bored quick, even though the page contains less words than this post……. http://www3.ul.ie/~rynnet/orthographic_projection_fyp/webpages/third_angle.html

1st angle, the object sits ON TOP of the page, and so rolling to the left, displays the right side of the object (assuming its a cube or simple shape)

3rd angle, imagine the object is under the page, rolling it to the right, displays the right side.

now if you think about 3rd angle from a 1st angle persons perspective, you can see where it gets its name from, as from a 1st angle persons way of working, you'd have to rotate the part 3 times to get an adjacent view.

If you look back to the cups, it should make sense now, page under…… page over etc. =) – the iso view is for folk who can't read 1st & 3rd angle and don't know the difference between a hidden line and a normal line as 1st or 3rd angle – doesnt matter, same information, different arrangement on the page!

Sry I'm editing like a bugger ignore what I just said, imagine a drawing of a dice with a printed symbol on each face. Lines and fetures wont position each face so unless you knew if you where look at a 1st or 3rd angle, you couldn't possibly arrange the symbols correctly as the draughtsman intended (maybe its loaded….. or why would it matter lol, loose example)

Also, yes 3rd angle is also acceptable in the UK, but as my boss and mentor would say if I turned out a 3rd angle drawing, "we don't work in imperial any more, its EN, not BS from here on"

Edited By Russ B on 06/03/2014 00:35:07

Edited By Russ B on 06/03/2014 00:43:36

[TJ55Participant @tj55]

Hi Everyone,

My first post!! although I have been keeping up with all subjects I have not found the need to throw in my tuppence worth, until now! The subject of 1st/3rd angle has had me puzzled (especially how to explain it) for quite a ling time. So I read through all the posts until I found some explanations that helped me understand. I don't profess to have the answer but a combination of 2 posts provided what I think is a very good way to look at the subject (then go away and think about it).

I took the diagram supplied in Coalburner's post 17/9/2012 12:16:19 and combined it with the explanation in Martin Kyte's post 17/9/2012 12:31:31 and this seems to explain it really well.

I understand everyone has a different way of learning but this combination did it for me.

Just my twopence worth, Thanks to Coalburner and Martin Kyte

[Mark CParticipant @markc]

Quote:

"3rd angle is only used America and Australia, the rest of the world uses 1st angle ortho – so not really that obvious, and not "as previously used in the UK" either – it really depends on your way of thinking."

Simply wrong, industry uses both (still, and accommodated in the standards) but predominantly 3rd angle is the default in mainstream use.

Mark

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

1st and 3rd can sometimes get a bit academic when working on real paper drawings .

Some engine parts might have several outside views , many sectioned views and numerous scrap views at odd angles .

Not the slightest hope of putting the views in the ‘right’ place according to the rules .

So all views are arranged as logically as possible and arrows indicating direction of view and other labelling is used to avoid any ambiguity .

It is not at all uncommon for the many views to be spread over several sheets .

Where possible the concept of 1st/3d projection is preserved but multiple views often end up anywhere .

For CAD drawings it’s a bit different . With an infinite sheet of ‘paper’ available many views can be projected and placed correctly on the master drawing . Problem arises now with running off real paper prints and getting subsets of views into reasonable logical order .

All good fun . Anyway some designers can do logical easy to read drawings and some produce a jumble of views – no amount of training or rule books appears to make any difference !

MikeW

[IanTParticipant @iant]

As my 2D CAD is generally just for my own use Mike, I'm afraid to admit that I never worry too much about which 'projection' I'm using. I just draw things as I see them in my 'minds eye'. Maybe I should try a bit harder and adopt one system (or the other) as my 'standard'. That list of things I should be doing is getting longer by the day…

IanT

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Ian ,

I used to do a lot of my work using hand sketched isometric views with one or two leading dimension on and nothing else at all !

Regards ,

MikeW

[Peter G. ShawParticipant @peterg-shaw75338]

My thoughts – as someone with NO engineering drawing training. (Nor engineering training either for that matter.)

I have Tubal Cain's Workshop Drawing (WPS 13) which explains it all reasonably well. Tubal Cain describes 1st Angle as "Natural", First Angle" or "English" projection "because it is the way children instinctively draw things". He then names the other system as American, or "3rd Angle Projection." Later on, he says that he uses 1st Angle as he finds it almost instinctive. I have to say that I disagree with this as it makes most sense to me to show what I am looking at on the same side of what I am looking at (if that makes sense). Therefore I always use 3rd Angle.

My suggestion to anyone struggling with this would be to obtain Tubal Cain's book, and, provided you can adapt to your own system, Derek Brown's book "CAD For Model Engineers", WPS 29. Together these will provide the amateur (which most definiely includes me) with all the information the amateur needs.

Regards,

Peter G. Shaw

[Jesse Hancock 1Participant @jessehancock1]

This is a British thing. We never drop the old way of doing anything which includes driving on the left. Although I see quite a lot of women trying to usually while talking to passengers. So much for multi tasking.

We should have dropped inches, pounds weight and currency years ago but no lets complicate what should be easy. And for crying out loud don't start on thead sizes, theads clothes, or this thread.

Jesse.

[David HaythornthwaiteParticipant @davidhaythornthwaite90386]

Hi Jesse,

I used to work in a British clothing factory doing 80% export. As soon as Metric became prevalent here (25 years ago), I metricated all our patterns (On CAD) to be up to date and be in line with most of our cutomers.

ALL our export customers asked us to supply garments in the old Imperial sizes as they wished them to appear authentic "Old British". To this date I think that you could count the number of Metric orders that we have made on the fingers of one hand!

It isn't always the manufacturer that is at fault. Try making a camera tripod with a metric thread. All the cameras have a 1/4" Whitworth thread.

David

[Neil WyattModerator @neilwyatt]

> All the cameras have a 1/4" Whitworth thread.

Except those with a 3/8" fitting

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by David Haythornthwaite on 20/01/2015 08:28:26:

All the cameras have a 1/4" Whitworth thread.

David

.

Regrettably, no longer true

As discussed, a while back, the "Standard" is now 1/4" 20 UNC, but specified to such a loose fit that it will accept a BSW.

MichaelG.

[MuzzerParticipant @muzzer]

It's funny. Canada is almost completely metric, much more so than the UK which is stuck half way between the imperial and metric systems (miles, pints, pounds etc). Yet like us they persist with imperial 3rd Angle projections presumably again as a result of their historical dependence on the US for so much of their goods and materials.

They also have a schizophrenic existence when it comes to the use of metric and imperial fasteners in products. Most Canadian-designed products are made outside of the US these days, so are generally designed in metric, yet it's pretty difficult to obtain metric fasteners locally in Canada, as they are so dependent on the US for materials. Played hell with my workshop activities when I lived there. Of course, in the UK almost all product design is metric thank goodness. With time, 3rd angle becomes second nature.

Murray

[Nigel McBurney 1Participant @nigelmcburney1]

When I started work the drawings were 1st angle,and the tech college taught 1st angle. I later worked for a US multinational which used 3 rd angle and did not find any difficulty using it,it took longer to learn the vast company dwg standards manual and US threads,later we changed to metric,though we did sometimes use standard parts which had been drawn up in some instances prewar,one young chap in the office came up to me some time in the 1980s with one of the standard dwgs which was a washer with a dimension of 11/64 ins can you help what does eleven over sixty four mean on this dwg? Another student had a query on drill sizes,again a fractional size ,I explained about fractional drills and also mentioned number and letter drills, he would not believe me that there were such drills and thought I was trying to set him up. It took a copy of machinery's hand book and various sample drills to convince that there were alternatives to metric drills.

[Neil WyattModerator @neilwyatt]

> I have Tubal Cain's Workshop Drawing (WPS 13)

I have that fine book, and some TC drawings and books that don't follow his own rules (e.g. projection symbols missing from almost every drawing).

Neil

[Enough!Participant @enough]

Posted by Muzzer on 20/01/2015 11:43:43:

It's funny. Canada is almost completely metric,

You think? Not in the manufacturing sector which is largely (dare I say almost exclusively) imperial. Naturally since our largest trading partner by far is the US. Go to a hardware store and nuts, bolts, screws etc are mostly imperial with a sprinkling of metric if you are lucky depending on the store.

Metrication is mainly in the supermarket, gasoline sales and highway speeds. (And at that, they had to produce special legislation for the gas station operators when we "went metric" in the 70's because they ignored it and continued to sell in gallons – imperial, not US).

Even our duty-free is oddball. The liquor allowance is 1.14 litres per adult which is actually 40 oz even though liquor and wine is almost exclusively sold in metric both here and in the States. There are a couple of distillers products that are made in 40 oz sizes (as well as metric), mostly for the duty-free trade so the situation is self-perpetuating.

Edited By Bandersnatch on 20/01/2015 23:14:07

[MuzzerParticipant @muzzer]

What I was trying to say was that the stuff manufactured anywhere outside of N America (typically China) is best designed in metric whereas anything manufactured locally (generally for local consumption) tends to be imperial. And for global export of products, you tend to need metric, particularly if those products are built into other products like vehicles.

I was engineering director for a Vancouver-based company until recently. Luckily everything was designed using metric dimensions and parts, generally for manufacture in China. Our customers were all over the world but even the American ones accepted metric fasteners etc on our products. As you say, trying to find metric parts locally is challenging and of course the same applies for tools. The selection available is a lot less comprehensive. My workshop now has a lot more imperial stuff in it.

A "pint" in a Canadian "pub"(??) never seemed to be quite the full measure – a result of a variety of a lot of conflicting regulations. The UK pint is about 20% bigger than the US pint (all shirt and no trousers), so not surprisingly that seemed to be what you found. And as for not being able to buy alcohol in the supermarkets….

Murray

[BowberParticipant @bowber]

As with so many things for my age group I've been taught both and had to use both (I'm 47) the same goes for metric and imperial measurements.
My wife gets a bit frustrated with me because I'll use the nearest convenient measurement so it's easier to remember, so I could measure a sign as 48"x 700mm, it really does her head in! If I'm making something in the workshop I'll use mm in preference though.

We were always told look here draw there, I also don't agree that 1st angle is more natural, I prefer 3rd angle and it makes more sense to me, however I'm happy using both.

Steve

[Peter G. ShawParticipant @peterg-shaw75338]

Steve,

I've 24 years on you and was taught imperial only. Realising the metric was coming, I deliberately set about building some kitchen cabinets using purely metric measurements. Since then I have always used metric wherever possible, but like you have no compunction in using imperial if it's more convenient.

The result now is that I'm actually more familiar with metric than imperial, and I often think in metric.

Rant mode on

What does annoy me though are those people who will not use the correct multipliers in metric, eg x1000 or /1000, millimetres, metres, kilometres. Instead we get abominations like 60cm. What's wrong with 600mm for heaven's sake? Ok, ok, I am aware that there certain dispensations for use in certain instances, but I don't like it, and I find myself automatically translating from cm to mm before I can understand it.

Rant mode off.

Cheers,

Peter G. Shaw

[Gordon WParticipant @gordonw]

There was a bit on the telly a few days ago, a big country house built about 1830. Architect was French. This was said to be the first house in Britain to be built in metric dimensions. The builders converted everything into Imperial. Must have been some job ,long before calculators. Probably a few mistakes as well.

[Neil WyattModerator @neilwyatt]

Engineers use millimeters for EVERYTHING on the scales we work to.

In the next MEW here are a couple of dimensions I converted from metres to millimetres – can you spot them?

Neil

[Ron ColvinParticipant @roncolvin83430]

Peter,

As to odd metric multipliers, our local river runs in a culvert as it crosses one of the towns recreation grounds. On the side wall of the culvert is a graduated scale showing the water level. It took me a while to work out that it was graduated in Decimetres, the only example that I have uncounted of this multiplier being used.

Ron Colvin

[Jon GibbsParticipant @jongibbs59756]

Hi Ron,

dm's make sense in the context of water when you consider that 1 dm^3 is 1kg.

You just need to keep the units and everything is clear.

As a kid of the 60's I was brought up on both systems transitioning around 11 from almost entirely imperial to entirely metric but it's made me comfortable with both systems and I know which I like best.

Jon

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