SIM Simultaneous requirement
Simultaneous requirement · Modificadores de zona · ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Note: SIM REQT on 6-hole pattern” states a simultaneous requirement requirement.
What controls
When two or more feature control frames reference the same datum reference frame, in the same order and with the same modifiers, ASME Y14.5 treats them as a single requirement: the part is set up only once and all those features are evaluated together in that datum reference frame, with their zones fixed relative to each other. In other words, the simultaneous requirement is the default, not something that has to be requested; the SIM REQT note appears mostly as a reminder or to restore it where it would not apply on its own, such as in the lower segments of composite frames. What matters is what it implies: you cannot realign the part between one frame and another to make each one come out better, because that allocates the error twice. What it does NOT do is merge the features into one or change the zone values.
How to verify
A single setup and a single construction of the datum reference frame for all the frames involved; the datums are probed once and all the features are then evaluated without realigning. In the software, the frames have to be grouped into a simultaneous requirement, because many packages evaluate each frame in isolation by default, which is more permissive. The equivalent physical check is a single functional gauge with all the pins for all the groups: if it goes on, the simultaneous requirement is genuinely met.
Common mistakes when interpreting it
- Realigning the part or repeating the best fit for each frame: that is exactly what the simultaneous requirement prohibits.
- Believing the SIM REQT note is needed for it to apply: in ASME it is the default behavior when datums, order and modifiers match.
- Assuming it still applies even though the modifiers in the frames are different: if they do not match, the requirements are no longer simultaneous.
How to get it in the workshop / if it comes out of tolerance
«SIM REQT» note or symbol on an ASME drawing. The holes in a pattern are evaluated together in a single datum reference frame. For the shop, it means the relationship between groups matters as much as the location of each group: machine everything that shares datums in the same setup and with the same work offset. It is the stricter of the two criteria, so it is the one to assume when the ASME drawing says nothing.
If each group passes separately and the whole fails, the error lies between groups: setup changes, table rotation, a different work offset for each operation or thermal drift over the shift. Machine the whole set in the same clamping or, if that is not possible, leave a machined reference to align the following operations. Also check the indexer position and axis backlash. And if the rejection comes from the report, first check that the CMM did not realign the part between frames.
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