Symmetry Annotation

[BridgeNut]

Hi,

I'm working on some drawings (making new drawings for reference) for a steel arch bridge built back in 1893, and have some of the original shop drawings.

On some of the drawings only one-half of the part is drawn (up to the Centerline) and noted: "SYM ABT CENTERLINE".

Am I right in assuming this means symmetrical about centerline, if so is this annotation still used today?, if not what else would be used.

Many thanks,

Gord

 

[fsincox]

I think you are safe in your assumption, it was common in the pre CAD days to have shortcuts like this in drafting practices. I was taught not to use section lines in my early career before we had modern CAD systems. The ASME standard fig. 1-33 shows a method for implying symmetry and I have heard it mentioned here before, but, I have never seen it used on a modern drawing.

 

[desertfox]

Hi Bridgenut

Yes your assumption is correct and I have recently seen CAD drawings using the same terms.

desertfox

 

[KENAT]

There is a GD&T symbol for symmetry as I recall though I believe it has wider application in ISO rather than ASME.

What you're talking about is subtly different but I think the idea is still shown in the relevant ASME spec whose number escapes me and I'm not at work to look.

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[dgallup]

I don't think the note is implying any GD&T constraint, simply that only half the bridge is drawn and the undrawn portion is a mirror image of the drawn portion.

My CAD system will make a half view and place 2 parallel lines at either end of a symmetry line per either ISO or ASME. I don't know which specific parts of the standards cover this.

 

[fsincox]

dgallup,
Y14.5M-1994 shows what you have described in the figure per my above statement.
Frank

 

[KENAT]

Thannks Frank I was thinking Y14.3 but as you say it's in 14.5.

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