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Drawing Projections

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Peter G. Shaw06/03/2014 14:45:40
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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 120/01/2015 07:52:09
314 forum posts

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 Haythornthwaite20/01/2015 08:28:26
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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 Wyatt20/01/2015 11:10:14
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> All the cameras have a 1/4" Whitworth thread.

Except those with a 3/8" fitting

Neil

Michael Gilligan20/01/2015 11:17:57
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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.

Muzzer20/01/2015 11:43:43
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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 120/01/2015 15:39:58
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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 Wyatt20/01/2015 15:56:42
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> 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

Bandersnatch20/01/2015 23:13:48
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1248 forum posts
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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

Muzzer21/01/2015 09:19:28
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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

Bowber10/05/2015 20:42:58
169 forum posts
24 photos

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. Shaw11/05/2015 11:11:17
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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 W11/05/2015 11:42:17
2011 forum posts

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 Wyatt11/05/2015 12:32:49
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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 Colvin11/05/2015 12:37:22
52 forum posts
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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 Gibbs11/05/2015 14:13:58
738 forum posts

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

AJS11/05/2015 14:50:28
32 forum posts

One of the reasons that CM are more popular than MM is because in school maths lessons CM are almost always used in examples and questions about measuring. Check out any primary or junior maths book for examples.

CM are also more understandable for youngsters in that they can easily see that 3cm is longer than 2cm, whereas if mm were used the difference is less obvious when drawn.

Alan

Mark C11/05/2015 15:33:02
707 forum posts
1 photos

Well I tried it Alan and no matter how hard I tried, drawing lines 3 cm long and 2 cm long or 30 mm and 20 mm I still get the same 10 mm difference.......

Mark

Gordon W11/05/2015 17:04:51
2011 forum posts

Centimeters are easier to visualise than millimeters. A bit like inches and 64ths.

Mark C11/05/2015 17:14:35
707 forum posts
1 photos

I don't have trouble with cm or mm I just see them in 2.54 cm or 25.4 mm lots!

Mark

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