Surface profiel callout with NO DRF
Surface profiel callout with NO DRF
(OP)
Typically, when we DO see datums specified on a surface profile callout, that tells us to set the part up to datums and measure the surface relative to those datums. No best-fitting allowed.
Also typically, if we DO NOT see a datum reference frame on a surface profile tolerance, that tells us we are allowed to best fit that surface onto its nominal shape, using all 6 DOF.
I have a situation where a surface profile tolerance is on a print with NO DRF. The customer is telling me that it is IMPLIED that this is wrt datums, even though none are specified.
Further, he claims this is part of his company's specs. I looked at the spec, but this situation isn't covered. But the spec does reference ASME 14.5M-1994. So I looked at the ASME spec. I couldn't find it in there either.
So my question is this --- what does the ASME 14.5M spec say about surface profile tolerances that do not reference datums? Is it IMPLIED that datums are specified, or does no DRF mean best-fitting is allowed?
Also typically, if we DO NOT see a datum reference frame on a surface profile tolerance, that tells us we are allowed to best fit that surface onto its nominal shape, using all 6 DOF.
I have a situation where a surface profile tolerance is on a print with NO DRF. The customer is telling me that it is IMPLIED that this is wrt datums, even though none are specified.
Further, he claims this is part of his company's specs. I looked at the spec, but this situation isn't covered. But the spec does reference ASME 14.5M-1994. So I looked at the ASME spec. I couldn't find it in there either.
So my question is this --- what does the ASME 14.5M spec say about surface profile tolerances that do not reference datums? Is it IMPLIED that datums are specified, or does no DRF mean best-fitting is allowed?





RE: Surface profiel callout with NO DRF
I would ask the customer to walk you through where in his company spec this is addressed.
RE: Surface profiel callout with NO DRF
There are situations where one could have a profile of a surface - all around - with, possibly, a surface reference datum. In another situation, one might have a profile without any reference datums on surface that are coplanar which means one must treat this as a single surface on a single plane.
Dave D.
www.qmsi.ca
RE: Surface profiel callout with NO DRF
Surface profile control can also be used without datum feature references as a form control. When no datum features are referenced, the tolerance zone applies where the part surface actually exists.
SeasonLee
RE: Surface profiel callout with NO DRF
RE: Surface profiel callout with NO DRF
"When necessary to relate linear and angular dimensions to a datum reference frame, the desired order of precedence may be indicated by a note such as: UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE RELATED TO DATUM A (PRIMARY), DATUM B (SECONDARY), AND DATUM C (TERTIARY)." This note is not to be used in lieu of indicating datum references in a feature control frame for geometric tolerancing applications."
My understanding of the last sentence is that implied datums for a profile of surface callout (which is geometric control) are not allowed. Datums must be specified in a FCF if the intention is to relate profile of surface tolerance zone with any datums.
RE: Surface profiel callout with NO DRF
Let's talk about the implied datum. A profile control may be used where it is intended to control two or more coplanar surfaces as a single surface, in this case an implied basic zero dimension exists between the coplanar surfaces that establish the true profile, the tolerance zone is a unilateral boundary extending away from the implied self-datum, a unilateral tolerance zone is automatic with an implied self-datum.
SeasonLee
RE: Surface profiel callout with NO DRF
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Surface profiel callout with NO DRF