First and Third Projection Symbols

[ShopShoe]

Random Thoughts:

I have been noticing that a lot of products in both the mechanical world and the construction world are sourced worldwide (or made for the world market) and not truly traditional in size. The sellers mark them traditionally, but as a user of multiple measuring systems I find that annoying. I was happy when that thin paneling was finally relabeled at the home center as 4mm and no longer sold as quarter-inch.

My "American Made" truck uses a lot of metric fasteners, making me glad that I started collecting metric tools back in the 1970s. Of course, the issue is further complicarted by the Torx fasteners and the other socket-head bolts which are not hex and not torx but something else entirely.

--

When it comes to the calibration of my eyeballs and the estimation of distances: I am very good with small parts in imperial and metric and feet/inches and mm/cm/meters in small areas but can't tell you how far any ball flew in any measurement in any sport. when I took Driver's Ed in High School I constantly got chewed out by the instructor by failing to understand when to do something when told in yards: Car-Lenghths and Block-Lengths worked better for me.

I am really good at liquid measure in both systems, thanks to lots of lab experience and talking to lots of doctors. What annoys me is dilution instructions for lawn products that combine tablespoons with liters per 100-gallons. I wish all dilutions were expressed in ratios: "Dilute 1:40" makes more sense.

--ShopShoe

 

[Jasonb]

But who wants to count out 40 spoonfuls of water to go with that 1 spoonful of concentrate.

 

[Jonathan Coates]

Most of my "drawings" are done in second angle on scraps of whatever is laying around which is where you need to look at the scribble from a second angle to tell what it was supposed to be. I've found by working alongside engineers around the world that you need to have a piece of paper to sketch on, rather than learn the technical terms for spigots, flanges, gussets etc. in several languages. If you take away sketches from job sites, very little gets done, it's a simple fact of building things that we swap thoughts through drawings, either cigarette packet sketches or 3D CAD models.

 

[paulrayner]

We have the fun fact that ply is sold as 1220 x 2440 but joists & studs are spaced at 400mm ctrs not the metric conversion of 16" so joints don't line up. plasterboard though is 1200mm wide.

I know drives you mad

 

[Bentwings]

In the drawings I create for work and for model engines, I like to envision an exploded view of an engine, and then arrange all the parts on the drawings in the approximate order that they are seen in the exploded view.

And I like to draw parts so that their mating surfaces are facing each other, often stringing several mating parts together across the sheet.

So I guess I sort of use a "what you see is what you get" approach.

For equipment in buildings, I draw things on the sheets as if I were looking down on the building from overhead, so that someone looking at my drawings does not need to physically rearrange the orientation of the equipment in their head in order to understand the adjacencies of equipment, how it is fed, and how the process flows.

Some engine drawing sets (and building/equipment drawings) that I have seen are drawn as if a bomb hit, and the parts are just scattered randomly.
There may be a valve next to a flywheel, with the valve springs many sheets away.
I would guess some folks just start drawing parts on sheets in the space available, with no consideration of organization, or grouping of related items/adjacencies.

For large working projects, it is a matter of necessity to rigorously organize things, else the project will quickly get out of hand.
And many others who are only marginally familiar with the project have to review my drawings, and so it must be clear to them, whether they are technical people, or layman.

And I like to spread out things on the sheet to allow for changes that occur during the design process.
I never try to fill up every inch of real estate on the page, but that format style does have its followers in some circles.
Rule #1 of drafting and design (for me anyway) is "Never paint yourself into a corner. Maintain elbow room at all times".

I must have been asleep in drafting class they day they taught symbols for first and thrird angle project.

.

Solidworks allows you to drop a part on the sheet, and depending on how it lands, then you can pull a projected view left, right, up, down, or at any one of four 45 degree angles for isometrics.

If you don't get exactly what you want, you can project off of the side of a projected view, but I seldom use that feature.

So I always use top, bottom, left, right, and one or more osometrics, and label each view as such.
Perhaps that is why some drawings confuse me; they don't have the left,right,bottom,top labels.

Once you have looked at a certain number of drawings though, it really does not matter how it is drawn, one can figure it out just by observation, especially if a few isometrics are included.

.I used the same logic .

Paper drawings were around for a while early in engineering once I discovered the cnc and shop guys did car they woul figure it out as long as Al features were shown somewhere the web paperless came in it didn’t matter the cnc guys just rotated the model around to best way to hold the blank . They examined the model for tools and set the tool changers up as needed. Ver seldom was even tolerance needed you knew what the machines were capable of and design tolerances into parts they with fit or you got a call to come out to the shop.for clarification

Only a few hole required boring most could be machined right to size once in a while you might have mis calculated a fit the you would hear on the phone het Mr smart engineer we got parts that don’t fit . If lucky you might say make it fit .

 

[gbritnell]

There is a great explanation of where first and third angle projection originated. There is also a great picture example of why first angle might get confusing. With all these replies you have to understand that in most cases we're talking about simple one or two sheet drawings. When you're working with an engineering drawing of an engine block that's 10 frames long (4 ft. X 12 ft.) Flipping views might become problematic. We're not talking about just a couple of holes beig rotated but all kinds of shapes and contours.

 

[petertha]

There is a lot of dual labeling these days, and I notice it a lot on wood products, but generally they break down something with nice round imperial units such as a 4x8 sheet of plywood to a very cumbersome 1219.2 mm x 2438.4 mm.

I've often wondered if lumber which Canada exports to USA is made for market inch based. Or if you are like most Canucks, have just been assuming they are 4x8's & 2x4's and any deviations are just typical tolerance of the brown stuff. It came as surprise to me that we have been making metric based construction products for a really long time. It just so happens to be real close to what we were used to growing up & we use the same labels. Not that a 2x4 was ever a really 2" x 4" anyway, which is yet another complication. Now with this new found knowledge, I model in metric & the woody parts fit better haha

https://cwc.ca/wp-content/uploads/2019/03/Plywood-Sizes.pdf

 

[GreenTwin]

Here is an article that talks about 1st and 3rd angle projection.

So it would seem that you could use any one of the four quadrants, and the fact that they use only the 1st and 3rd quadrants for projection just seems totally random and arbitrary.

Why not use 2nd and 4th angle projections too?

Why two different standards that show the same thing?

Very odd.


https://wonderfulengineering.com/di...ngle-projection-mechanical-engineer-explains/

 

[Jasonb]

Pat although they show the same thing, projection is about the relationship of each of those three (or more)and where they are placed not the actual three (or more). Hence why they are arranged differently on th epage.

A lot depends on the part you are drawing, a simple rod may only need two views to show an end is round and how long it is. Something like an engine cylinder could want 4 or 5 views (4 sides and the end) and maybe a section but the position of those will be determined by the projection used.

 

[Iampappabear]

A vote for metrification.

Having sailed my whole adult life, I have done my share of navigation and I am talking the old school typre using charts, bearings and of course the 360 degree compasse. For the non sailors of the group, 1/60 of 1 degree on the compasse equals 1 nautical mile on the earths surface, not the easiest numbers to work with.

If instead of 360 degree compasse they used 400 degree compasse, 1 degree on the compasse would equal 100 kilometers, so much easier to work with.

Of course we are now in the era of GPS and chart plotters very few nauticats ever look at their compasse far less their paper charts.

As knots and 360 degrees are the language of the skys.... as is English of coures , this system will never change so no conversion to meteric.

At the risk of boring you, a piece of string taken from the north pole to the center of Paris, France, would be 4,000 kilometers long.

Colin

 

[ajoeiam]

A vote for metrification.

Having sailed my whole adult life, I have done my share of navigation and I am talking the old school typre using charts, bearings and of course the 360 degree compasse. For the non sailors of the group, 1/60 of 1 degree on the compasse equals 1 nautical mile on the earths surface, not the easiest numbers to work with.

If instead of 360 degree compasse they used 400 degree compasse, 1 degree on the compasse would equal 100 kilometers, so much easier to work with.

Of course we are now in the era of GPS and chart plotters very few nauticats ever look at their compasse far less their paper charts.

As knots and 360 degrees are the language of the skys.... as is English of coures , this system will never change so no conversion to meteric.

At the risk of boring you, a piece of string taken from the north pole to the center of Paris, France, would be 4,000 kilometers long.

Colin

AIUI - - - that's what the original rationale was - - - except they found that it ain't quite so.

(Seems that its about 4574.94 km at least according to www.distance.to )

 

[peterl95124]

I'm currently looking at a factory drawing of an IC engine head, in the center is a top view, below that is a port-side view, above that is a starboard-side view, problem is by following the rules the starboard-side view is upside-down :-( !!!, so actually very confusing, also by following the rules the front end view is on the left and its rotated from its installed orientation, this time not confusing but definitely weird.

 

[Jasonb]

It's not a problem related to the projection used but the person who laid it out, probably to fit the paper size better without getting too small.

The two sides and two ends could all have been laid out horizontally (correct way up) with the plan view above or below depending on 1st or 3rd but that would need wider paper

 

[Daryl_bee]

A vote for metrification.

Having sailed my whole adult life, I have done my share of navigation and I am talking the old school typre using charts, bearings and of course the 360 degree compasse. For the non sailors of the group, 1/60 of 1 degree on the compasse equals 1 nautical mile on the earths surface, not the easiest numbers to work with.

If instead of 360 degree compasse they used 400 degree compasse, 1 degree on the compasse would equal 100 kilometers, so much easier to work with.

Of course we are now in the era of GPS and chart plotters very few nauticats ever look at their compasse far less their paper charts.

As knots and 360 degrees are the language of the skys.... as is English of coures , this system will never change so no conversion to meteric.

At the risk of boring you, a piece of string taken from the north pole to the center of Paris, France, would be 4,000 kilometers long.

Colin

The use of degrees predates any distance measurement and comes from ancient Babylonian astronomy (probably before). Readings, calculations and tables were done in degrees, minutes, seconds, thirds, fourths, & fifths etc. Predating excel etc (imagine making tables lengthy enough to be bound into books) 60 is very convenient as it is divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 & 60. The attached pic, as an example, shows a table going to "ninths". The system is accurate, convenient and has served well for many thousands of years.

BTW the Earth is not a sphere but an oblate spheriod so when divided (N/S) into +/-90 degrees the distance varies so...not a great standard for today. Especially considering we're using extremely accurate GPS which, by necessity, factors in relativistic (variable) time rates to achieve that.

 

[kf2qd]

First angle is used by the British and Europeans, while the Americans and Canadians do it correctly and use 3rd angle.

Making parts for windmill towers is fun, they come from Spain and Germany and the first thing I have to do with any drawing is convert to 3rd angle to eliminate the confusion...

 

[GRAUBELE]

Hello kf2qd

I think there is no right or wrong here.
But it's like the saying: There are many ways to Rome.
You're right, in Germany the first angle is usually used.

Best regards from Germany
Dieter

 

[Richard Hed]

Hello kf2qd

I think there is no right or wrong here.
But it's like the saying: There are many ways to Rome.
You're right, in Germany the first angle is usually used.

Best regards from Germany
Dieter

I can use both ways, however, I believe 3rd angle is intuitively easier.

 

[Daryl_bee]

First angle is used by the British and Europeans, while the Americans and Canadians do it correctly and use 3rd angle.

Making parts for windmill towers is fun, they come from Spain and Germany and the first thing I have to do with any drawing is convert to 3rd angle to eliminate the confusion...

The worst I had was once at work (years ago) I had to create a fairly involved cad model from a supplier datasheet. The border stated (in words) it was third angle projection. The part was drawn in first angle projection. You can't imagine the head scratching that went on until I finally clued in. We had to go back to the supplier to get them to correct their drawing for our database.

 

[Steamchick]

I was involved for 4 years interpreting Japanese drawings for European suppliers... checking the European drawings gave the parts that the Japanese drawings intended. I made one mistake in projection, where the main projection was in 1st angle, but one sub-drawing in the middle was a view in 3rd angle, with a small note across the other side of the sheet to explain! The note was missed by the UK supplier's time-served 30-year experienced draughtsman who re-drew his drawings in 3rd angle, and by me. So the parts were wrong... Duh! The suggestion was the Japanese draughtsman had originally got the projection wrong when he drew the sub-part, so a later amendment was the addition of the note saying "sub-part xxx was 3rd angle". Pre-CAD, 1988. Ho Hum. Nobody died.
K2

 

[ShopShoe]

For a time, I was involved in arranging instruction in CAD for High School instructors. We had a discussion on the first coffee break about all this and the consensus was that once one could get past the "way we were always taught" it is not really that important EXCEPT that any supplier of drawings needs to agree on and standardize the conventions that will be used in that environment and/or for a client that wants it a certain way.

Why did I say that above?

The business world wants to be paperless and 3-D modeling is where the design is originating: With 3-D models any type of 2-D output can be generated and annotated for a specific use or purpose and models are becoming the method of communication instead of drawings, except when drawings are required to be submitted.

--ShopShoe