Creating a dimension with MMB

To properly compute the MMB size of datum B, there should be a geometric tolerance (probably orientation) controlling datum feature B with respect to primary datum A (at RMB). You must add this dimension in PC-DMIS before the one in question. If there is no tolerance, PC-DMIS will effectively assume an orientation tolerance of 0 at MMC as this represents a mating situation and is the most conservative assumption.

To properly compute the MMB size of datum C, there should be a geometric tolerance (probably position) controlling datum feature C with respect to primary datum A (at RMB) and secondary datum B (at MMB). You must add this dimension in PC-DMIS before the one in question. If there is no tolerance, PC-DMIS will effectively assume a position tolerance of 0 at MMC for the same reasons as above.

All you have to enter for the limits of size are those that are seen on the blueprint for each datum feature. MMB size is a combination of feature size limits and geometric tolerances as described above.

Since your tertiary datum is referenced at MMB, it must be a feature of size and thus cannot be a plane. There is nothing requiring the tertiary datum to be a plane in PC-DMIS software.

The (M) for the feature would be .5136 +0.0003/-0.0002, for instance. What features are A B and C. I assume A is a plane, and B and C are holes? You need to know the size and tolerances of B and C in order to apply correct MMB to those features.

Thanks for your help. bfire85 you're correct. A is a plane and B and C are holes. Attached is the datum B and C information.


That's what pc-dmis ask me for.

in this case what values exactly do i have to put in? Sorry, i'm from Portugal (english is not my primary language) and i really want to know if i've understood correctly.

Thanks for your help. bfire85 you're correct. A is a plane and B and C are holes. Attached is the datum B and C information.

{"data-align":"none","data-size":"large","data-attachmentid":485740}
That's what pc-dmis ask me for.

{"data-align":"none","data-size":"medium","data-attachmentid":485741}

Do not put anything in for the <size>. Go into the other tab, depending on what version you are using it is either Nominals or Advanced...enter the tolerances in there.

Thanks bfire85 . That really helped me a lot.

Just one last question. It's normal that the feature appearence of Datum C to be the one bellow (like it was a flat feature)?

Just one last question. It's normal that the feature appearence of Datum C to be the one bellow (like it was a flat feature)?


{"data-align":"none","data-size":"large","data-attachmentid":485752}

No. Are you sure CYL_C is truly a cylinder? Can you post the code from Cyl_C.

Note: When naming dimensions, only use numbers, letters, and/or underscores. Spaces, hyphens, and special characters typically don't work well for PC-DMIS.

If you want to use the MMB for the datums, you will need to put in the size. The tolerances are added in the Advanced or Nominals tab, as bfire85 mentioned(it's good to tell us what version of PC-DMIS you are using as things change from version to version.)

I see the tertiary datum look like C does when it's not facing the same direction as the primary and secondary datums, like a side hole.

The code is here:

CYL_C =FEAT/CONTACT/CYLINDER/DEFAULT,CARTESIAN,IN,LEAST_SQR
THEO/<2.4034,0,0>,<0,0,1>,0.283,0.3
ACTL/<2.4034,0,0>,<0,0,1>,0.283,0.3
TARG/<2.4034,0,0>,<0,0,1>
START ANG=0,END ANG=360
ANGLE VEC=<1,0,0>
DIRECTION=CCW
SHOW FEATURE PARAMETERS=NO
SHOW CONTACT PARAMETERS=NO