TP with nx

[Sa-Ro]

Refer below image

I have a rectangular block. Two drill on opposite faces are same parameters (dia and location)

Is it valid to mention
2X dia 5
TP|dia0.1|A-M|B-M|C

Datum C is identified in one surface only.

Or shall I mention 2X INDIVIDUALLY at datum C and FCF?

 

[mfgenggear]

@Sa Ro
far as mfg yes, the manufacture would be forced to square up the blocks for mfg and for inspection.
it would require making the face parallel & square for tooling

 

[Sa-Ro]

I am unable to understand. Please explain in detail.

 

[mfgenggear]

for manufacturing and inspection
when machining the hole on face -C- the machinist will hole the opposite face to -C- and two surfaces , -A- & -B- clamped with a machinist vice.
when machining the hole opposite face -C- the machinist will hold the part on -C- and -A- & -B-
inspection will follow a similar procedure to inspect the part.
thus all surfaces must be square & parallel to get correct true position.

 

[chez311]

Sa-Ro,

I assume you mean |A(M)|B(M)|C| with A and B at MMB since there is no datum feature M shown. The dashed notation is reserved for multiple datum features.

inspection will follow a similar procedure to inspect the part.

This is not necessarily the case. With A and B at MMB, there is no requirement to clamp on these faces during inspection due to datum feature shift. As a result there is some strange behavior which could be construed as violation of datum precedence - float/shift is allowed from A and B due to MMB, however the part must contact C. There could be a conceivable situation where the part makes no contact with A or B but full 3 points contact with C. If this reflects function then fine, if not then you may want to consider why C isn't primary.

Or shall I mention 2X INDIVIDUALLY at datum C and FCF?

If you want them to be verified separately, use INDIVIDUALLY. If you want the 2X features to be treated as a pattern, remove it. Either is valid, it just depends on your requirements.

 

[mfgenggear]

@chez311
of course agreed, but it is done all the time in manufacturing, theoretically datum -c- could be probed by CMM
but it is easier by location on and opposite face the 3 datums verified, 3 constraints established. dimension will be held
by manufacturing to a tighter tolerance for tooling so that the engineering drawing requirements fall in.
at the end as specified on the drawing the requirements are satisfied. I have and still do this often.
there is tolerance stack up, and is common to tighten the dimensions on the print to allow stack of dimensions to fall in
and it can and does get complicated.

 

[Sa-Ro]

Thank you.