Check Dimension

[Casa250]

Hello,
it seems a simple question but I fail to find any concrete answers on this online.
If a drawing show a dimension with rounded brackets it is referred to to be a "checking dimension".
When "100%" is added then this would mean that all parts are checked, so 100%, correct?
When "SPC" is added then this would mean that a large number of parts are manufactured, then measured and then the capability cpk derived from it to understand the process capability thus getting a confidence that the process is stable and not all parts need to be measured but only a few, say for each batch or at the beginning of each shift etc, correct?
So now, if there is only the rounded brackets but no SPC or no 100% the official information I find state that this means "needs to be measured". My question is, how often? Is there a standard / ISO that defines this or do we have to specifically clarify this with the supplier?

Thanks!

 

[Gr8blu]

A "check dimension" such as you describe is usually for a surface or distance that is readily measured - but is buried somewhere in among a bunch of other dimensions that are not so readily verified after manufacture / assembly. It is called a "check" because the exact measurement isn't important as long as the remainder of the surfaces / distances that define it ARE within correct tolerance.

As an example: If I handed you a stick that was exactly 1 meter long, with two marks on it (one at the 15 cm position and one at the 65 cm position), the resulting "check" dimension would be the distance you could measure between the two marks: 65-15 = 50 cm.

As a further example: If I handed you the same stick without telling you it was exactly a meter long, but gave the distance from mark to end AND the distance from mark to mark, then the overall length (1 m) would become the check dimension.

Converting energy to motion for more than half a century

 

[Belanger]

If by rounded brackets you mean parentheses, then it's a reference dimension and it should not be measured.