Metric dimensioning convention

[unclesyd]

Not having been metrified early on I have recently ran across a little something in the use of the metric system that I have found no answer for.

We have a process with sevral very large tubular reactors where all the dimensions are in mm, over 1000 dimensions on
one print. Every equipment piece is dimensioned in mm nothing Else. We have other equipment that all dimensions are also all in mm.
The question come from some prints that crossed the table this week that originated in Europe that carry dimensions in meters and cm's, no mm's. The prints have locations that are referenced to 115.16 cm while that the larger dimensions are 10.25 meters.

What is the convention when calling out metric dimensions of equipment?

 

[ctopher]

I think depends on the size/type of equip. I have seen large equip dim to meters and cm, smaller dim to mm.

Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)

 

[unclesyd]

The size factor is what is one of my problems as the above mentioned reactors have a bolt circle of 9145 mm. As I posted everything else is in mm's.

The other reference is also some large equipment with the mixed dimensions sans mm's.

 

[ctopher]

I think it is a bad idea to mix dims. It could create errors during mfg. I would have the main dim shown, then the other as reference.
i.e. XX mm/[XX cm]

Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)

 

[MechNorth]

Y14.5M-1994, Section 1.5.1 SI (Metric) Linear Units..."The commonly used SI linear unit used on engineering drawings is the millimeter." It doesn't preclude the use of m or cm, but those are more common in architectural work from what I've seen.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[ewh]

Unfortunately, these are European drawings, and probably have no relation whatsoever to ASME Y14.5.

 

[ctopher]

I agree. But, I can't remember what the standard is in Europe.

Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)

 

[MechNorth]

Here's some ISO standards to check; ISO 128 - Technical Drawings; General Principles of Presentation, ISO 129 - Engineering Drawings - Dimensioning - General Priniples, Definitions, Metods of Execution, and Special Indications. These were referenced i ISO 1101-1983 (the primary document for ISO GD&T).

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[PeterCharles]

In my view the only dimensions to use are millimetres and metres.

 

[namdac]

The method used should state the dimensions as so:
XX mm (XX cm/M) either one is acceptible in any machine shop. The one I work for prefers mm, why, I don't know. My personal belief is all the metric system is base 10. Nothing more, I have engineers that have 4-5 different scales, I myself only have 1. This is the easiest dimensioning one can do. The rest of the world is doing very well with it. Why don't we use it regularly? Because we have the lasiest people in the world that can't throw that foot and inch tape measure away. We have lobbiest in washington dictating the way we should do things. We here were converting to metric, spent three years developing procedures...blocks...etc. Then the lobbiest convinced congress. Guess what happened we still have to design and build in english. What a waste...
Regards,
Namdac
P.S. Had to vent sorry.

 

[gearguru]

Metric technical drawings unit is mm.

 

[KENAT]

mm is I believe most common and was all I ever saw in the UK on technical drawings when doing metric. I think it's in BS8888 which in turn references about 50 other BS, BS EN and BS EN ISO specs.

The continental Europeans (and if I recall correctly Japanese) seem to have a fondness for all the other metric units & derived units. I'm pretty sure I've seen French technical info in cm. I've even seen continental European stuff in dm, that's decimeters for our imperial friends

IMO meter is by far the best metric unit to use for calculations etc as it removes any factors. When doing calcs a lot at uni I was so used to 10^x etc that I didn't think twice, so could have happily used it on drawings now my brain takes a while to figure it out so I wouldn't think of straying from mm (plus of course it's in the standards)!

As long as it's clear which dims are in cm and which are m or even mm I don’t' see it as a major problem. I'd much prefer it to be consistent, at least on each drawing, but I'd hope anyone using engineering prints can multiply and divide by 10, 100 or 1000 easily enough.

At school in UK up to about 13-14 it was almost always cm, with m just for 'big things'. Once science got more technical it was all m with 10^x as required, this continued to university. Once I got into the work place it was all mm. Plus at home it was mainly yards, feet and inches.

To this day when measuring stuff at home I use whichever scale on the rule corresponds most closely with the point I want to measure to!

When it comes to drawings it's all just marks on a scale, inches, feet, yards, meters, cubits.... As long as I know which I'm using I'm fine, I don't get all the fuss.

Like I said though when it comes to calcs give me meters any day.