Drawing Projections

[AJSParticipant @ajs]

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 CParticipant @markc]

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 WParticipant @gordonw]

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

[Mark CParticipant @markc]

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

Mark

[Neil WyattModerator @neilwyatt]

> 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.

That's because field staff need to be able to read the depth by eye without binos and from a distance. levels from gauging stations are usually reported in metres to the nearest millimetre.

Neil

[Ian AbbottParticipant @ianabbott31222]

I'm 68, we were taught both at school and I happily use both now, but for the life of me, I can't visualise in a thousand years measurements such as 27,493mm.

I'm much happier with 60cm than 600mm. And never 1,435mm for standard gauge, that's an insult to every pioneering British railway engineer…….

Ian

[JasonBModerator @jasonb]

Posted by Neil Wyatt on 11/05/2015 18:10:36:

>

That's because field staff need to be able to read the depth by eye without binos and from a distance. levels from gauging stations are usually reported in metres to the nearest millimetre.

Neil

Should that not be reported in metres to 3 decimal places

Edited By JasonB on 11/05/2015 18:46:17

[Edgar Vin 1Participant @edgarvin1]

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.

[David Clark 13Participant @davidclark13]

The easiest way to learn metric is to do railway modelling when you are young. (4mm to the foot.) I have been using imperial and metric for the last 48 years or so with no problems.

Edited By David Clark 1 on 13/10/2015 16:24:39

[norman valentineParticipant @normanvalentine78682]

I am in agreement with Peter Shaw. The SI system uses multipliers of 1000. Centimetres are not part of it. I am a retired teacher of design and Technology and always insisted that the kids used millimetres not centimetres. I tried to convince the maths department to teach in millimetres but to no avail.

Before becoming a teacher I worked in the Packaging Industry, initially in inches, down to sixteenths. After we converted to metric life was much easier, we worked in whole millimetres and working out overall sizes was so much more straightforward without having to use fractions.

[Trevor Drabble 1Participant @trevordrabble1]

Wolfie,

Sure I got some old technical drawing books which would help you . If you interested , will try and sort one out for free for you and take it with me to Midlands Exhib on Friday .

Trevor.

[Neil WyattModerator @neilwyatt]

Posted by norman valentine on 13/10/2015 17:55:09:

I am in agreement with Peter Shaw. The SI system uses multipliers of 1000. Centimetres are not part of it. I am a retired teacher of design and Technology and always insisted that the kids used millimetres not centimetres. I tried to convince the maths department to teach in millimetres but to no avail.

That's because centimetres are used in exams… (not the real world…)

Neil

[Paul LousickParticipant @paullousick59116]

When I started my career as an apprentice we used feet and inches and fractions of an inch. Then was told that we were changing to a metric system. No problem I thought. 0.5 of an inch = 1/2 inch, 0.25 inch = 1/4 inch. (WRONG !!)

My wife is a dress maker and works in centimeters not millimeters (can't convince her otherwise) but as a mechanical engineer/draftsman, I use metres and millimeters, Mechanical engineering drawings are normally dimensioned in millimeters. Example: 10, 50.8, 50.01, 150, 1250, 20000 (or unless specifically shown otherwise as 20m).

Machine shop drawings should be dimensioned in millimeters not in centimeters. (eg. 100.01 millimeters, not 10.001 centimeters and absolutely never 1.0001 decimeters)

Paul.

[V8EngParticipant @v8eng]

Whatever would furniture stores do if they could not use Centimeters!

My Smileys seem to have stopped working, oh well it is getting too late to worry about things like that.

Edited By V8Eng on 13/10/2015 23:25:08

[brickyParticipant @bricky]

The building trade converted to metric in the early seventies ,and is in metres and millimetres always.We still got windows in imperial and tried to fit them to a metric gauge for brickwork 75mm bed and brick ,it could be frustraring until all suppliers got their act together.I still order timber as 3mt of 4" by 2" and metrication has given the suppliers of building products an excuse to reduce the thickness of timber ,screws,nails and others to numerous to mention.Try matching floor joists in an old building with metric materials .

Frank

[Neil WyattModerator @neilwyatt]

You have to get it right, or this is what happens:

Edited By Neil Wyatt on 14/10/2015 10:58:12

[Gordon WParticipant @gordonw]

When I built my w/shop a few years ago I phoned the yard and asked what size the ply sheets were-1.2 x 2.4 was the answer. So foolishly I put the studs in to suit then bought the ply- 8 x 4 of course.

[Speedy Builder5Participant @speedybuilder5]

My dad used to say "You can't imagine Kg / Sq Meter, Pounds per Sq Inch was simple. It was a ladies high heel treading on your toe! By the way, here in France, the Cm is used quite frequently by implication. I was questioned when I went to buy some glass 850 x 400 x 6 thick, as they thought it was for a shop window, but couldn't understand why i wanted it so thick ! (8.5m x 4.0m x 60mm thick).

[BaldricParticipant @baldric]

Posted by Gordon W on 14/10/2015 10:59:25:

When I built my w/shop a few years ago I phoned the yard and asked what size the ply sheets were-1.2 x 2.4 was the answer. So foolishly I put the studs in to suit then bought the ply- 8 x 4 of course.

I did a similar thing but different, I spaced the timbers at 8×4 having found out the size of the ply, then found that plasterboard to go on the ceiling is 1.2 x 2.4, consistency would have been helpful….

Baldric

[Neil WyattModerator @neilwyatt]

"Don't worry Sir, it will ride up with wear."

Neil

[norman valentineParticipant @normanvalentine78682]

Yesterday I went to buy some 4mm set screws. The conversation was quite interesting. The length of the screws was discussed in millimetres by one and inches by the other. The funny thing was that neither of us batted an eyelid at the different units. They didn't have what I wanted, damn.

[john carruthersParticipant @johncarruthers46255]

> but couldn't understand why i wanted it so thick ! (8.5m x 4.0m x 60mm thick).<<

Pavement light?

I still have a few Hayward lights (the big old cast 2" x 3" prisms in purple glass? )

Edited By john carruthers on 14/10/2015 17:29:53

[steveteeParticipant @stevetee]

You have to remember that the first version of the metric system was the CGS system , centimetre / gram /seconds as base units. At school I learnt about fluid densities in grams per cc for example and indeed engines sizes are still measured in cc's or litres. Then during my school career it all changed to the MKS system , metre kilogramme second became the base units. Out of this grew the SI system which is what we use now , with complete harmonisation of all units around the base units. So out with Maxwells Henrys erg and dynes and in with Webers, Coulombs and Joules ( he was a salford brewer you know). They still use Whitworth threads on BSP fittings and no has ever come up with a better system, and long may it persist.

[LimpetParticipant @limpet]

Last time I purchased timber it was in metric feet (300mm) but then I am in Devon​ ​

[W J HallParticipant @wjhall48713]

As someone who was at school before metric became standard I have never really mastered cms, despite doing O-Level early enough to encounter CGS. For ordinary life I tend to think of things either in imperial, or, after a career in engineering, in mm. However, I did measure something in cm today, so there is hope yet.

Although it is a very sensible system there is a problem with the metric multiplier abbreviations. It is all very well laughing at the press when they write mg for micrograms, or use the everyday m for million where M might have been better, but really, who thought a system with three multipliers with vastly different values, all, abbreviated to various forms of 'm' was practical?

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