GD&T mathematically defined datum.

[mekengineer]

I have a customer defining datums with zero tollerance gd&t.

Is this considered a mathematically defined datum?

Is this type of callout leagal per ASME or ISO standards?

Please see the attached sketch.

 

[drawoh]

mekengineer,

Locating a Ø4mm hole with a zero angle tolerance looks wrong to me. The angle tolerance is a run-out specification for a surface.

You should use position to locate a hole. What controls the 50mm dimension between B and C?

JHG

 

[fsincox]

ASME, I do not believe so, zero tolerances are allowed with a material modifier, angle of a centerline no.

 

[fsincox]

If I understand what he wants he achieved that with the basic dimension the angularity just adds confusion to the issue.

 

[pmarc]

mekengineer,

1. The way how angularity tolerance is shown on your customer's print is incorrect per the newest editions of ASME and ISO GD&T standards. The leader of perpendicularity feture control frame should not be attached to a centerline, an axis or whatever it is. It has to be associated with a real feature of the part (e.g. surface). At the moment it is really hard to guess which element has to be controlled by this tolerance.

2. Specifying 0 angularity tolerance without (M) or (L) modifier is illegal because it is unrealistic. Such callout implies that at any circumstances there is no space for angularity deviation, so the characteristic has to be perfect. Since there is no perfect manufacturing process, any tolerance (even very very small) has to be specified.

 

[mekengineer]

Thanks. You all have confirmed my suspicions.