gd&t tolerances of symmetry

[Fabrizio Magi]

Bye to all,

I have a doubt about how to define a symmetry tolerance in the attached design.
I would like to define the symmetry of the appendix with respect to the symmetry axis of the cylinder. for reasons of simplicity of reading of the table, I would prefer to use the notation to the right, but I do not convince myself of the use of symmetry regarding an axis that in figure collapses on a point.

Thank you.

 

[MassiVonWeizen]

you can not give a symmetry to a diameter because the axis of a circle can be rotated 360° and therefore is not defined.
quote the width of the plate and put in datum on that. then you can tolerate the hole with the lease if necessary

 

[MassiVonWeizen]

I said cows.
Make a hybrid: datum in the left view and tolerance in the right view

 

[Fabrizio Magi]

I said cows.
Make a hybrid: datum in the left view and tolerance in the right view

Well, then it is also worth putting directly the datum in the right view. for a control, a datum is a datum regardless of sight. .
On the other hand, I think that a tolerance of symmetry, given compared to an axis that in the view where the tolerance itself collapses at a point, is not good.

 

[New Rider]

I would put the datum on the horizontal axis.
do you have a way to check after the quota or any discrepancy?

 

[antonio_sc]

Well, then it is also worth putting directly the datum in the right view. for a control, a datum is a datum regardless of sight. .
On the other hand, I think that a tolerance of symmetry, given compared to an axis that in the view where the tolerance itself collapses at a point, is not good.

the datum is an axis,the axis is a set of points (despite the projection of the axis on the plane and a point). Therefore, we always refer to the axis in both the one and the other view. Despite the most formal way to indicate the datum axis is the one expressed in the figure of the left (among other things the axis should be indicated in that view, but I know that you did not do it because the design is to be completed).

 

[Fabrizio Magi]

the datum is an axis,the axis is a set of points (despite the projection of the axis on the plane and a point). Therefore, we always refer to the axis in both the one and the other view. Despite the most formal way to indicate the datum axis is the one expressed in the figure of the left (among other things the axis should be indicated in that view, but I know that you did not do it because the design is to be completed).

Of course!
So from what you say, regardless of the view I use, I’m saying that the median plan of the two faces of that appendix must pass (unless tolerance) for the axis. That's all. for you there is no margin of error from those who control. Thank you.

 

[PiE81]

where to place the datum is indifferent, but as written by antonio_sc, the axis in the left view should be indicated.

said that, in this case it could be more correct to use a localization tolerance. but this is for you to decide; In general, for slots as key locations, tabs (referred from the shaft axis) is sufficient (and much more used) a localization tolerance.
symmetry tolerance is more restrictive. I attach the example you can find on y14.5 asmes.

 

[exxon]

I would do as written by mvw

datum in the left view and tolerance in the right view

But I'm not convinced you can't put the indication of the datum directly in the right view, for two reasons:

- I did not find explicit prohibitions on this;
- the indication is uniquely interpretable.

I follow this with interest.

 

[Fabrizio Magi]

Okay, guys. I confirm that on the vademecum of the mechanical designer hoepli I found this image. the case is closed. (?)

 

[PiE81]

do not take it, but it is not the right approach. the fact that there is an example on a vademecum counts little.
you need to understand what it takes to ensure that you do not insert too restrictive or useless tolerance. symmetry is also controlled by localization and is probably the most suitable one. studies the asthma already mentioned to fully understand its differences.

 

[exxon]

the case is closed. (?)

I would say no, at least for me: what you posted in #10 does not bend, but I wonder if you can indicate the datum on the size of the diameter as in #1 on the right. I don't see contraindications, but I've never seen it in any design.

 

[PiE81]

I would say no, at least for me: what you posted in #10 does not bend, but I wonder if you can indicate the datum on the size of the diameter as in #1 on the right. I don't see contraindications, but I've never seen it in any design.

you are possibile.

 

[exxon]

is the reference in the norm? You know where?

 

[Fabrizio Magi]

do not take it, but it is not the right approach. the fact that there is an example on a vademecum counts little.
you need to understand what it takes to ensure that you do not insert too restrictive or useless tolerance. symmetry is also controlled by localization and is probably the most suitable one. studies the asthma already mentioned to fully understand its differences.

I'm not disregarding what tolerance I need, whether it's too restrictive or not. the question in #1, which I may have poorly exposed, concerns the table of that tolerance. doubt is whether symmetry compared to an axis that becomes a point can have multiple interpretations.

that the vademecum comes into play. There is a design that has a cylinder whose axis in the view is a point. This axis, in the same view, is a datum. and this datum is called for symmetry.

 

[Fabrizio Magi]

taken from asme y14.5 2009

 

[exxon]

Thank you.
(temporary blindness... only explanation for not seeing it before... )

 

[Fabrizio Magi]

What do you say? I am satisfied. However if you find other examples are welcome!