I'm with
JacobCheverie on this one. Unless you can provide concrete evidence to back up your assertions, please refrain from stating that PC-DMIS is calculating datum shift incorrectly. This is not the first time you have made such unfounded assertions which is why I am stepping in now to prevent the spread of mis-information.
PC-DMIS calculates datum shift in accordance with ASME Y14.5 (see extract from Y14.5 - 2009 below - a similar statement appears in Y14.5 - 2018 section 7.11.11).
4.11.9 Datum Feature Shift/Displacement
MMB or LMB modifiers applied to the datum feature
reference will allow the datum feature to shift/displace
from the boundary established by the datum feature simulator
in an amount that is equal to the difference between
the applicable (unrelated or related) actual mating envelope
for MMB, actual minimum material envelope for
LMB, or surface of the feature and the datum feature
simulator. The datum reference frame is established from
the datum feature simulator and not the datum features.
See Fig. 4-17 for LMB, Figs. 4-18 and 4-24, datum feature
B in Fig. 4-26 for MMB, and Fig. 4-30, illustration (b) for
the surface. The datum feature shift/displacement shall
always be limited or constrained by the datum feature
simulator. If the datum feature simulator geometry is
such that it does not fully limit or constrain the feature
such as rotating away from the datum feature simulator
beyond the established boundary limits, as shown in
Fig. 4-31, illustration (c), then the feature must remain
in contact with the datum feature simulator, and datum
shift or displacement is not allowed. See para. 4.16.7 and
datum feature A in Fig. 4-28.
NOWHERE within the standard does it say to "simply add" the MMB to the feature bonus as this would be wrong, resulting in the acceptance of bad parts. Take the example below, showing the position of two holes relative to a central cylinder at MMB. It shows the holes out of position and would result in zero datum shift because they are off location in opposite directions. If we were to simply add the bonus from datum C to the positional tolerance it would result in the holes being incorrectly accepted and the part would not assemble.
With legacy position, you are able to control whether datum shift is applied or not and it is possible to add the bonus from the datums to the positional tolerance. However, the help is very clear in pointing out that this functionality was added at a customer's request, purely to allow them to provide process adjustment information and is not compliant with ASME Y14.5
I'm with
JacobCheverie on this one. Unless you can provide concrete evidence to back up your assertions, please refrain from stating that PC-DMIS is calculating datum shift incorrectly. This is not the first time you have made such unfounded assertions which is why I am stepping in now to prevent the spread of mis-information.
PC-DMIS calculates datum shift in accordance with ASME Y14.5 (see extract from Y14.5 - 2009 below - a similar statement appears in Y14.5 - 2018 section 7.11.11).
4.11.9 Datum Feature Shift/Displacement
MMB or LMB modifiers applied to the datum feature
reference will allow the datum feature to shift/displace
from the boundary established by the datum feature simulator
in an amount that is equal to the difference between
the applicable (unrelated or related) actual mating envelope
for MMB, actual minimum material envelope for
LMB, or surface of the feature and the datum feature
simulator. The datum reference frame is established from
the datum feature simulator and not the datum features.
See Fig. 4-17 for LMB, Figs. 4-18 and 4-24, datum feature
B in Fig. 4-26 for MMB, and Fig. 4-30, illustration (b) for
the surface. The datum feature shift/displacement shall
always be limited or constrained by the datum feature
simulator. If the datum feature simulator geometry is
such that it does not fully limit or constrain the feature
such as rotating away from the datum feature simulator
beyond the established boundary limits, as shown in
Fig. 4-31, illustration (c), then the feature must remain
in contact with the datum feature simulator, and datum
shift or displacement is not allowed. See para. 4.16.7 and
datum feature A in Fig. 4-28.
NOWHERE within the standard does it say to "simply add" the MMB to the feature bonus as this would be wrong, resulting in the acceptance of bad parts. Take the example below, showing the position of two holes relative to a central cylinder at MMB. It shows the holes out of position and would result in zero datum shift because they are off location in opposite directions. If we were to simply add the bonus from datum C to the positional tolerance it would result in the holes being incorrectly accepted and the part would not assemble.
With legacy position, you are able to control whether datum shift is applied or not and it is possible to add the bonus from the datums to the positional tolerance. However, the help is very clear in pointing out that this functionality was added at a customer's request, purely to allow them to provide process adjustment information and is not compliant with ASME Y14.5
