ISO GPS - Concentricity with reference to a planar face? 1

[201181]

Hi,

Firstly, apologies for the bad drawing enclosed (CAD system is currently down)...

Anyway, I was just thinking about something I came across when working at my previous company (a large global leader in fluid control), and would love anothers opinion. Part of my job was to apply GPS to 2D drawings, and this is something I have a few years experience with. One thing I seen at this particular company, which I had never seen before was using a concentricity tolerance, which also referenced a perpendicular, planar face. I have drawn a very basic example of what I typically saw on some drawings, and I was just curious, has anyone ever seen this before?

My understanding is that coaxiality references an axis and concentricity references a point, where only the corresponding axis (or combined axis to make a common axis reference such as A-B) or point is the reference for the tolerance frame. I understand it is normal to add a concentricity tolerance to one diameter axis, which references another diameters axis (for example, a diameters axis referencing datum A as per my sketch), so I thought it was strange to also reference a planar face (datum B on my sketch), which is at 90 degrees to the A axis. I cannot find any examples of this anywhere else (web and reference books).

Please look at the sketch and tell me what you think, as I would love to know if anyone else has seen this (perhaps I could learn something).

Many thanks in advance

 

[pmarc]

Although it is not illegal to have B inside coaxiality callout, it adds no value in this case.

It would have certain meaning, if was referenced as primary datum feature, that is, if coaxiality callout was |COAX|dia. 0.1|B|A|.

Side not: diameter symbol is missing in front of coaxiality tolerance value on your sketch.

 

[TheTick]

Is there a compelling reason to use concentricity instead of runout? I would wager they are measuring runout and calling it concentricity anyhow. (Never lost this bet!)

 

[pmarc]

Something that should back up my previous reply - snapshot from ISO 1101:2004 (page 39).

http://files.engineering.com/getfil...213-f033e0f02145&file=iso_1101_coaxiality.png

The same is shown in ISO 1101:2012, figure 151, page 80.

 

[201181]

Many thanks for the replies (yeah, I know the Ø symbol is missing, I was rushing my very lame excuse for a sketch ).

Must admit, I didn't spot that in the ISO 1101 standard, so thanks for finding it. As is mentioned above, concentricity is not really favoured by me over run-out either. However, just so I understand the ISO example (and my own bad example), is the axis on the planar face just trying to say that the 0,1 toleranced axis is central to the planar face of datum B? Isn't the reference in the tolerance frame already saying this by referencing datum A, hence making any reference to a planar, perpendicular face irrelevant? It just still seems a little confusing to me to reference a planar face.

Many thanks again for your input.

 

[pmarc]

Reference to planar perpendicular datum is relevant as long as that datum is primary in the coaxiality callout. Attached graphic shows two cases and the difference in geometrical interpretation of coaxiality wrt |B|A| and wrt |A|.

http://files.engineering.com/getfil...f-0cc2d86048e4&file=iso_1101_coaxiality_2.png

Let me know if it helped.

 

[201181]

Hi pmarc, that did help alot, thanks very much (I'll be saving those pictures in my reference material )

 

[SeasonLee]

pmarc

Your sketch and explanation makes us easy to understand, I like it.

Season

 

[fsincox]

I agree with the other thread,
How about an interrupted feature, sure, in ISO all bets are off!
We always look at simple parts and make these simple on purpose the real world is not as neat and clean!! We need standards that will also address the real world parts, IMHO!
Frank