Tolerance symmetric Dimension to centerline

[321GO]

Hi Guys,

I need to tolerance two opposing symmetric features with regards to their common centerline. The tolerance must be equal for both features.

Suppose i placed the tolerance only on one feature. Would it be obvious for the machinist that the opposing feature has the same tolerance (with regard to the centerline)?

Or better tolerance both features independent with regards to the centerline?


Thank you all!

 

[Enginerd9]

... and as "Enginerd9" says...lol

 

[pmarc]

As far as I see (basing on lettering orientation and so on) OP is following ISO standards. In ISO standards symmetry tolerance is a special case of position tolerance so it has exactly the same interpretation as position, but it is specifically used for two features shown coplanar on a drawing. So simply said these two controls do not have different meanings like in Y14.5 std.

If I had to follow ISO standards I would use dia.82H8 feature as a datum feature A (but maybe dimensioned a little bit different that I am not using imaginary extension lines) and assign symmetry for 58.8 dim.

If I had to follow Y14.5 std, I would do similarly with one exception - position callout instead of symmetry.

 

[fsincox]

32160,
1) Are you interested in controlling the location of the surfaces only, location of the centerplane derived, orientation of the surfaces/centerplane or form?
2) Is the ID diameter you reference real (hidden) or just an extension of the radii for dimensioning purposes?
3) Do you really not care about the relationships to the OD?
4) is this for a mating fit? How does it mate?
Welcome,
Frank

 

[fcsuper]

I would do:
-establish a and b datums
-a dim across the flats
-apply a positional tol to that dim that references a and b

Datum a should be the perpendicular plan which these features pierce. Datum b could the outside dia. I realize the outside dia may not be functionally important, but imagine how this part will be fixtured while it is being made.

Another option is to use datums a and b and apply a profile tol to the entire interior (rounds and flats together).

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

http://groups.yahoo.com/group/solidworks & http://twitter.com/fcsuper

 

[321GO]

First off this feedback is priceless, realy

- yes, this is according our ISO standard
- the ID has two flats sides, i see the previous setup gave rise to misinterpretations, my mistake to make.
- i simply want to center the centerline of the flats to the center of the ID (or otherway around, the hole with regard to the centerline of the flats).

Pls see attachment. what do you think, is the sketched tol.zone a coorect interpretation of the GD&T sheme used?

 

[321GO]

@ewh

Yes, that makes sense. Pls see attachment.

p.s. i do lot's of drawings, but never came across this before and want to be sure what i do makes sense.

Thanks again.

 

[pmarc]

321GO,

If you want to control location (symmetry) of centerplane of flats in relation to ID the second scheme (4.jpg) is incorrect - you are controlling location of the axis of ID in relation to centerplane of flats.

First scheme (3.jpg) is the one you should choose, but you have to delete either position or symmetry feature control frame and leave only one of them - these two controls you put have exactly the same meaning in ISO standards so it does not make any sense to use both of them. A decision which to choose (position or symmetry) is only up to you. It is also good idea to add concentricity (position) control of OD relative to ID.

 

[321GO]

Hi pmarc,

"these two controls you put have exactly the same meaning in ISO standards so it does not make any sense to use both of them"

Yes, i know. I did it to emphasis the fact.

 

[pmarc]

321GO,

One control is for sure enough. Adding something extra can only cause a lot of confusion.

 

[321GO]

pmarc,

fully agree. My intension was to reiterate that they have the same meaning, not to use both.



Thank you all!