Position Tolerance Called to Datums with MMC

jameslaz

Involved In Discussions
#1
I have a question regarding a position called out to datums that have a MMC modifier. From what I have read is seem like any bonus tolerance shifts the allowable position tolerance location from the stated datum. What I need clarification on is this. Is I have a feature called out with a position to datum A at MMC and say datum A is dimensioned 1.000 +/-.005 from my feature and I get .002 bonus tolerance from datum A. Does that mean I can be 1.007 (1.000 +.005 tolerance + .002 bonus tolerance = 1.007) from datum A and still be good? I hope this is clear enough to understand.

Thank you for any help,
James
 
Elsmar Forum Sponsor

Michael_M

Trusted Information Resource
#2
Max material condition adds to the tolerance frame not to the feature size. The tolerance frame dictates 'where' the hole is located. Max material allows for more 'error' in location.

For example, you have a 1.000 +/-.005 hole with a tolerance frame of .005m A Bm C. For our example, the 1.000 hole is right at 1.000

The hole diameter gives an additional .005 so your .005 frame adds another .005 giving a total of .010. So your dimension could read 1.000 +/-.005 TP .010 A Bm C. The tolerance frame changes every part depending on the actual diameter of the 1.000 hole.

If the hole diameter is .997, the feature frame would be TP .007 A Bm C


Bm is a bit more complicated. I will say datum B is another hole. As this diameter gets bigger, you add more tolerance to the feature frame. If datum B is another 1.000 +/-.005 hole, it adds to the feature frame. Depending on they type of feature datum B is, hole, slot, boss, plane, etc, this can really confuse things.

To keep my sanity, I typically only calculate max material from the actual feature itself and not from any bonus datum's (unless I really really need it). However, if I really need the bonuses from the datum's, someone did not make the part well.
 

Proud Liberal

Quite Involved in Discussions
#3
The bonus only applies to the positional tolerance. The size tolerance is not increased. The bonus = (actual feature size) - (nominal size @ MMC). Also note the bonus cannot exceed the total size tolerance. The bonus stops accumulating when the size of feature reaches the LMC limit of size.
 

jameslaz

Involved In Discussions
#4
Thank you the answers but I still don't understand what is gained by any bonus tolerance from a datum with a MMC modifier.

I have attached a small sketch that I hope will help.

Looking at the sketch. if the datum C dimension is at 2.495 how would that affect the position callout of .005 to A, B and CMMC?

Thank you again,
James
 

Attachments

Michael_M

Trusted Information Resource
#5
In essence, the print you have is incorrect. The 2.500 and the 1.500 dimensions should not have tolerance. They would be basic (wrapped in a square).

The true position frame is what gives the 'tolerances'.



Maybe off topic: How to calculate true position.

Take the error of X and square it, add to that, the error of Y squared. Take the square root of the sum and multiply by 2. This number needs to be less than or equal to the feature frame reference.

Example: the 2.500 is actually 2.4983, the 1.500 is 1.5025, and the .500 hole is .502.

The .502 gives us a 'bonus' of .007 as it is .007" over the smallest hole size allowed. This directly adds to the .005 from the frame meaning the frame is .012.

the error of 'X' is .0017 (which we square getting .00000289). The error of 'Y' is .0025 (which we square getting .00000625). We add .00000289 + .00000625 getting .00000914. We take the square root of this number .00302 and double it getting .00604 (we double it because our calculation uses radius and we need to convert to a diameter).

This formula may look familiar as the Pythagorean therm (Asquared + Bsquared = Csquared).
 

jameslaz

Involved In Discussions
#6
let me try one more time with a new sketch that shows the actual part (sorry I had to block off a lot of it for proprietary reasons).

As you can see I have a diameter .220 +/-.005 with a position callout of .014 to A, B-MMC and C-MMC.

On the print the A datum is called out as 1.180 +/-.002, the B datum is a diameter 5.1893 +/-.0010 and datum C is a diameter called as .477 reference dimension.

You can see my confusion. We have problems with the parts and I am trying to see if any bonus tolerance can help. I do not know what to do with the MMC for datums B and C.

Thank you,
James
 

Attachments

Thread starter Similar threads Forum Replies Date
F Position tolerance check gage manufacturing Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
L GD&T Bonus Tolerance - Checking True Position of a Pierced Hole Inspection, Prints (Drawings), Testing, Sampling and Related Topics 9
C Using a Pin Gage to check True Position of Inline Holes, Design, Tolerance. Etc Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
J Datum B and C are each both vertical and horizontal - Tolerance of Position Question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
optomist1 Tolerance of Position - Pattern of Holes at MMC - Datum Feature Reference Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
A Bidirectional True Position Tolerance Call-Out for Holes for Process Capability Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
G Clarification on Position with Bonus Tolerance - Feature Control Frame Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
J CMM Programmer position - Baltimore Maryland Job Openings, Consulting and Employment Opportunities 0
T Question about Quality Department employee position titles Quality Manager and Management Related Issues 10
L Form-dependent position prevention control FMEA and Control Plans 1
B Minitab Type 1 Gage Study on True Position Question Measurement Uncertainty (MU) 1
M Informational EU – Official position on EUDAMED delay Medical Device and FDA Regulations and Standards News 3
F Position of Quality Manager - Can the organization's Quality Lead be shown as Quality Manager of the lab as well? ISO 17025 related Discussions 5
Proud Liberal Cp / Cpk on position using multiple MMC bonuses Capability, Accuracy and Stability - Processes, Machines, etc. 2
F Conversion of coordinate dimension holes to position dimension Design and Development of Products and Processes 3
B Design of fixture checking including Position of hole and slot General Measurement Device and Calibration Topics 5
CCaantley Stepping Down from my quality manager position soon After Work and Weekend Discussion Topics 18
was named killer AS9100 FAIR - True Position hole out by .0011" on 50 parts AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
M Informational COCIR Position Paper Harmonisation of Standards for Medical Devices Medical Device and FDA Regulations and Standards News 0
B True Position Measurement Inspection, Prints (Drawings), Testing, Sampling and Related Topics 9
F Holes position inspection - Calculation of centre distance and plug sizes of a gauge Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
M Position paper Team NB Statement - Patient safety EU Medical Device Regulations 0
P True Position vs X and Y Dimensions Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
Q How to perform Process Capability for true position Statistical Analysis Tools, Techniques and SPC 10
Ron Rompen Ford Method - Position Capability with MMC Modifier Capability, Accuracy and Stability - Processes, Machines, etc. 14
M True Position / GD&T - I'm staring at this drawing and I'm lost Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
O How to deal with Multiple Datums - Position with respect to Multiple Datum Feature Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
J New position and AS9100 audit is 1 month away- need advice AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 8
Proud Liberal Cpk on Position w/ MMC on Location and Size Capability, Accuracy and Stability - Processes, Machines, etc. 3
E Position of a milled hex - Print Callout Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
N True Position of slot Boundary with MMC Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
J True Position Question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
N Procedure for determining pinhole position in condom Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
M Measuring the True Position of a Cylinder's Pierce Point Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
M Offered Management Position - Limited Experience - Any Concerns? Quality Manager and Management Related Issues 13
C Dose Mapping - How to relate back to Routine Monitoring Position ISO 13485:2016 - Medical Device Quality Management Systems 3
T Optical Comparator measuring of Position of a Threaded Hole Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
A Shall I apply for this job position (Quality Manager)? Career and Occupation Discussions 5
E Composite Position Calculation on a 12 X 4 Hole Pattern Inspection, Prints (Drawings), Testing, Sampling and Related Topics 13
M Manager IMS (9001, 14001, 18001) Position in Organisation Chart ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 17
V GD&T Interpreting Datums in Two Single Segmented Position Tolerances Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
M True Position and MMC (Dilemma Between Engineers) AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
D Just starting out looking to get into a quality engineer position Career and Occupation Discussions 2
P MDD position on Final Inspection/Release Employee Experience/Training EU Medical Device Regulations 1
S Tab to circle True Position? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
S GD&T Callout for Diametrical True Position Manufacturing and Related Processes 6
S Moving to a New Company for a New Position Coffee Break and Water Cooler Discussions 3
M Zero Tolerancing on True Position using MMC (Maximum Material Condition) Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
L ASME Y14.5 Coaxial Feature Toleranced with Position w/o Reference Datum Design and Development of Products and Processes 2
M Surface Profile and True Position Question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5

Similar threads

Top Bottom