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Parallelism in ISO12129 without base indication

Parallelism in ISO12129 without base indication

Parallelism in ISO12129 without base indication



Im review ISO 12129-2:1995 and I'm confuse with T3 parallelism tolerance and indication on the drawings.
What it's mean, where is base and how looks tolerance zone in this case.
For those who do not have access to this standard please find similar drawing example from refrence thread.
For me it looks like mixed of internal and "out of dated" standard.
How to read it?


RE: Parallelism in ISO12129 without base indication

I am going off the memory, but I think the shown practice is no longer allowed in ISO.
Please confirm, if you don't mind. You are the SME in ISO.

Thank you pmarc for your support.

RE: Parallelism in ISO12129 without base indication

Not to step on pmarc's toes, but yes -- that is not allowed in ISO.
I don't think that method was ever allowed, because it doesn't have the datum triangle as the base for one of the arrows. So it's completely ambiguous. At one time (1983 version), ISO allowed for the method shown in my attached PDF. But that was dropped eventually.

Another confusing thing: That seems to be a cylinder, so parallelism doesn't really seem appropriate anyway. I get that they're trying to control taper, but I don't think that's the use for parallelism, which needs a datum.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Parallelism in ISO12129 without base indication


Probably in 1101:2005 this kind of method was withdraw from ISO. In spite of this I'm curious what is a base in this case when we assume that one arrow is a triangle. I assume that base is a section line and tolerance area lies between two parallel lines to this section line?
Please find below picture drawn according to this still active standard!

RE: Parallelism in ISO12129 without base indication

Parallelism symbol applied to cylinder supposed to mean "parallelism of the generating lines"


Using second arrow instead of "toilet plunger" symbol means that it doesn't matter, which side to use as a datum (which kind of makes sense in case of a cylinder).

Both practices seems to be confusing, so they are abandoned by now, but may be found on older drawings.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

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