Using the virtual condition of slot as datum
Using the virtual condition of slot as datum
(OP)
Drawing is attached. In question is the size of the datum pin to simulate datum -c-. My customer is saying that the size should be the VC of the slot (6.15 x 9.15) and that a separate gage to check the FCF at that slot is not needed. Should I be using a slot pin that only takes the MMC of the width of the slot (9.9) and use a separate gage to check the VC of the slot as it pertains to the a and b data?





RE: Using the virtual condition of slot as datum
When using datum C as a tertiary datum, one needs a pin the VC size and not the MMC size.
Dave D.
www.qmsi.ca
RE: Using the virtual condition of slot as datum
Would it not be better to use the width of the slot as datum C?
If this were my drawing, there would be separate positional tolerances for the width and length of the slot. I cannot see how the length could be part of a tertiary datum.
JHG
RE: Using the virtual condition of slot as datum
To check these FCFs there would need to be two gages employed.
RE: Using the virtual condition of slot as datum
No, Your customer is correct. If you wanted to use a 6.9 X 9.15 slot type pin or diamond pin your print should look like the one attached. I added the basic angle to help clarify the orientation of datum feature -C-.
Paul
RE: Using the virtual condition of slot as datum
When one confirms that the slot is in position relative to datums A and also B, the gauge pin in this fixture is the virtual condition size, shape and orientation (that explains the term "BOUNDARY"). If the gauge pin can be placed in the slot without due force, then the slot becomes datum C.
The tertiary datum C in our case is for orientation only. Datum B (secondary) is the intersecting point of 2 perpendicular planes and all dimensions come from it. Yes, I would only use the width of datum C rather than the complete boundary but the width would be its virtual condition size.
The reason I wouldn't use the complete boundary for datum C is the fact that there could be a conflict with datum B in one direction. One must make sure that the pin in datum B is able to float in any direction without a constriction from datum C. Again, datum C is only used for orientation.
Hope this helps.
Dave D.
www.qmsi.ca
RE: Using the virtual condition of slot as datum
RE: Using the virtual condition of slot as datum
If I were the Designer, I probably would have had the width of the datum C slot as datum C rather than the full slot. There could be a conflict between datum B and C the way it is drawing right now.
Dave D.
www.qmsi.ca
RE: Using the virtual condition of slot as datum