GD&T Bonus Tolerance - Checking True Position of a Pierced Hole

L

Liger

#1
I am checking true position of a pierced hole back to two other datum holes that are used at MMC. The inspection is being done using PCDMIS software, and for some reason, the bonus tolerance from only one of the datum holes is being applied. Should we not get the MMC bonus tolerance from both holes added together? Spec is: .034TP to D(M) and E(M). My PCDMIS report shows bonus tolerance of .0015 for D and .005 for E, but is only applying the .0015 as the total allowable bonus. Since the drawing gives both datums at MMC, should we not be receiving the total .0065"?
 
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Stijloor

Staff member
Super Moderator
#2
I am checking true position of a pierced hole back to two other datum holes that are used at MMC. The inspection is being done using PCDMIS software, and for some reason, the bonus tolerance from only one of the datum holes is being applied. Should we not get the MMC bonus tolerance from both holes added together? Spec is: .034TP to D(M) and E(M). My PCDMIS report shows bonus tolerance of .0015 for D and .005 for E, but is only applying the .0015 as the total allowable bonus. Since the drawing gives both datums at MMC, should we not be receiving the total .0065"?
We can help you, but to avoid all confusion, please attach a sketch of the call-out including the datum references. You can not arbitrarily add a bonus from both holes to the controlled hole. Datum shift is not an easy concept and is often misinterpreted.
 

Stijloor

Staff member
Super Moderator
#4
Thank-you for your reply Stijloor. Hopefully I got the attachment on this response.
The attachment shows the callout, but not the datum features.
Can you attach the actual drawing with confidential information removed?
 
L

Liger

#5
I am checking true position of a pierced hole back to two other datum holes that are used at MMC. The inspection is being done using PCDMIS software, and for some reason, the bonus tolerance from only one of the datum holes is being applied. Should we not get the MMC bonus tolerance from both holes added together? Spec is: .034TP to D(M) and E(M). My PCDMIS report shows bonus tolerance of .0015 for D and .005 for E, but is only applying the .0015 as the total allowable bonus. Since the drawing gives both datums at MMC, should we not be receiving the total .0065"?
My apologies. See if this helps.
 

Attachments

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D

Dooglas

#8
I have attached a portion of a customer drawing that defines some positional characters for hole locations. The general tolerance is ?.015 inches but I am unclear how to interpret the tolerance provided concerning the locations of the (88) ?.390 holes and the (8) tapped holes.
I also have to report dimensional results in my PPAP reports and want to make sure I report this properly. Any help would be appreciated.
 

Attachments

D

David DeLong

#9
I don't know where you are getting the 0.065 accrued tolerance but it does appear that your software is, somehow, accruing the tolerances on the datum holes. Most equipment will not calculate the "bonus" tolerance on datum holes and use them in RFS mode. That is the reason a checking fixture would accept a product while the CMM would reject it.

All the dimensions come from the D datum (secondary) and the E datum (tertiary) is used for orientation or anti-rotation only.
 

Jim Wynne

Staff member
Admin
#10
I have attached a portion of a customer drawing that defines some positional characters for hole locations. The general tolerance is ?.015 inches but I am unclear how to interpret the tolerance provided concerning the locations of the (88) ?.390 holes and the (8) tapped holes.
I also have to report dimensional results in my PPAP reports and want to make sure I report this properly. Any help would be appreciated.
There's a problem because there are no basic dimensions associated with the position callout and the person who drew the thing used baseline dimensioning for the holes, which muddies things even further. You have contradictory specifications which should be cleared up before you go any further.
 
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