Symmetrical Dimension 1

[Dave K]

I just saw something "new" on a drawing, and before I question it(and the detailer), I'd like to know if this is common, or from some standard. I've done a search, a google search, and looked thru y14.5, and have not found it.

The part on the drawing is symmetrical, so all of the dimensions that show symmetrical features read like this "=1.000=", with a tiny equals sign, before and after it.

I've seen the symmetrical centerline used, per y14.5, but never these little equal signs.

Thanks,
Dave

-Dave
Everything should be designed as simple as possible, but not simpler.

 

[ewh]

That's a new one on me. Just ask the detailer what standard it came from. If this use isn't documented somewhere, change it to something that is.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ringster]

Genman,

Perhaps the company has it own standard which will provide a clarification. Otherwise, in these days of computer generated drawings, my opinion is that symmetry symbol on a drawing should be avoided.

I have never seen the method you described. Over 50 years.

 

[ctopher]

The equal signs were made up from who drew it. They should be removed.

Chris
SolidWorks 08, CATIA V5
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion

 

[KENAT]

Is it a German thing, or maybe Japanese. I vaguely recall seeing it somewhere. It's not ASME as far as I know, unless 14.5M-2009 slipped it in, which I doubt.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[Dave K]

I know it's not a company standard, since I've been establishing that myself (there was no formal standard). I'll talk to him when he returns later this week...maybe it's a British thing? he did go to school in the UK.

Given that none of you have seen it before, and I've never seen it...unless he comes up with a good source, it's out.

Thanks everyone!

-Dave

-Dave
Everything should be designed as simple as possible, but not simpler.

 

[KENAT]

I went to school in the UK and don't remember seeing it there on formal drawings at least.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[fcsuper]

There's two ways to callout symmetric in Y14.5. Use the Symmetric FCF, or with symmetrical outlines. I've seen all kinds of ways individual try to extend symmetrical applications in dimensions. Every non-GD&T short hand scheme i've seen is fundamentally flawed and unenforcable.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[dino3]

We use this method here as a way of dimensioning symmetrical features. The centre line needs to be drawn and indicated as a reference plane. It is is part of our company standard, and cuts down the dimensioning clutter on some of our drawings.

Dean Viviani

 

[ajack1]

This could well be a British thing, it was fairly common years ago in the days of boards and pencils, but I have not seen it on a CAD generated drawing.

I doubt it applies to any recognised standard.

 

[naresh843]

hi dave..

Those types of symbols are nothing but a symbolic representation for symmetry..most of the american companies doesnt follow or use such things..but european countries like..italy,german,,etc use such symbols..they give more importance to those symbols..if you can open the attached image here,,take a glance,,in such situation we can delete 2.5mm dimsn both sides and keep =5=,,which makes clear view,,this is much concern when we do drafting for typical profiles or when the detail is meshy



sorry for grammer mistakes

 

[Dave K]

naresh843: That is exactly what his symmetrical dimensions look like, thanks.

all: As a side note, at a past employer, we used a centerline, and the note "Sym about this plane UOS", before they went to Y14.5.

-Dave
Everything should be designed as simple as possible, but not simpler.

 

[fcsuper]

naresh843,

In your example (which is common in the U.S. as well), if the both 2.5's are removed, there is no tolerance to the centerline, and therefore the hole and the centerplane itself is essentially undimensioned. Unless a standard or drafting manual specifically states the centerline splits the tolerance (or in some other way is toleranced), any further dimensions off the centerplane would have no tolerance applicable to them.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[CheckerRon]

Gunman: I like your first response. Dump those european symbols and use Y14.5 method.

 

[naresh843]

hi fcsuper

I agree with you..when the hole is tolerated,then its should be essntially given 2.5mm dimension with tolerance,..In other task when hole is not tolerated,i think that is ok????



sorry for grammer mistakes

UG NX5,SOLID WORKS

 

[juergenwt]

Dimensioning as per DIN 406 / ISO 129. Symmetric parts.