# How to calculate MMC when is placed after datum

R

#### Reality99

Hi,

I'm trying to calculate MMC for one dimension, but honestly speaking I forgot how to do it.
Our CMM routine is not calculating automatically, and we have few true position and profiles out of spec, but I see that MMC is not being considered, even though the drawing calls for it.

This is the example:
Female hole
3.4 +/- 0.1 MM Actual result is 3.42
TP 0.2m A Bm

And datum B is another female hole:
6.7 +0.2 -0 MM Actual result is 6.92
TP 0.4m A Bm

Basically I forgot how to do the calculation in paper . I know that these are simple operations.
To clarify, I'm looking how to calculate bonus tolerance in TP's.

Thank you.

Last edited by a moderator:

#### Michael_M

Trusted Information Resource
Hi,

I'm trying to calculate MMC for one dimension, but honestly speaking I forgot how to do it.
Our CMM routine is not calculating automatically, and we have few true position and profiles out of spec, but I see that MMC is not being considered, even though the drawing calls for it.

This is the example:
Female hole
3.4 +/- 0.1 MM Actual result is 3.42
TP 0.2m A Bm

And datum B is another female hole:
6.7 +0.2 -0 MM Actual result is 6.92
TP 0.4m A Bm

Basically I forgot how to do the calculation in paper . I know that these are simple operations.
To clarify, I'm looking how to calculate bonus tolerance in TP's.

Thank you.
for max material, take the actual and subtract the smallest. in your example, 3.42 - 3.3 is .12. this is added directly into the true position. In your example, .2 + .12 means you have a true position of .32. for the Bm (and for simplicity) you will do the same thing. However, be careful of Bm. It is not always as simple as taking the actual and subtracting the smallest, depending on how it is called out and what the print actually makes 'B'. I typically will use max (or least--calculated; largest - actual) on the TP .2m and will not add any max from Am Bm Cm. it has gotten me in trouble before.

Last edited:
R

#### Reality99

Ok, now I got it. But what about Bm? There is no additional bonus from Bm in the first TP?
The other hole has a 0.42 mm bonus tolerance, so I'm wondering if it should be taken in consideration for first TP.

T

#### True Position

Ok, now I got it. But what about Bm? There is no additional bonus from Bm in the first TP?
The other hole has a 0.42 mm bonus tolerance, so I'm wondering if it should be taken in consideration for first TP.
The MMC bonus tolerance on secondary and tertiary datums does not give you additional position tolerance, it allows your datum reference frame freedom to shift or rotate to accept the part.

Similar to how you'd rotate a part slightly to get it to fit on a position gage.

#### optomist1

##### A Sea of Statistics
Super Moderator
True Position is right on, this is = Datum Shift

B How to calculate Cpk on Perpendicularity (Cyl Tol Zone at MMC) Capability, Accuracy and Stability - Processes, Machines, etc. 32
M How to calculate a True Position toleranced at MMC - Capability of True Position Statistical Analysis Tools, Techniques and SPC 12
How to calculate Effective Number of People for ISO 13485 Certification? General Auditing Discussions 2
Need to calculate tolerance Intervals with a set of non-normal data and 3-Parameter Weibull distribution Using Minitab Software 0
Calculate acceptance of equipment reading after calibration General Measurement Device and Calibration Topics 2
Calculate acceptance of calibration reading Measurement Uncertainty (MU) 1
How would you calculate this? Capability, Accuracy and Stability - Processes, Machines, etc. 4
Bend allowance formula to calculate per degree per radii Manufacturing and Related Processes 2
Commercial excel templates that calculate overhead, hourly rates, fee proposal Excel .xls Spreadsheet Templates and Tools 0
M How to calculate benefits? Moving some developed non controlled software/automation systems Service Industry Specific Topics 2
Calculate number of people in processes, considering cycle time/takt time = quantity of people Lean in Manufacturing and Service Industries 9
How to calculate the maximum allowable hysteresis of a pressure gauge General Measurement Device and Calibration Topics 1
S How to Calculate the producer Risk AQL - Acceptable Quality Level 25
Methods to Calculate Available Production Rate ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 0
Why calculate LCL in P-chart? Statistical Analysis Tools, Techniques and SPC 4
How to calculate CPK with n = 1 Manufacturing and Related Processes 2
Add-On software for VMC to calculate setting time, Idle Time, OEE etc.. Manufacturing and Related Processes 2
L How to calculate the Probability of Deficiency of the AQL of an Inspection AQL - Acceptable Quality Level 16
V How to Calculate Unbiasing Constant C4 Statistical Analysis Tools, Techniques and SPC 1
J How to Calculate OEE Indicator for a Workshop (15 Machines) Lean in Manufacturing and Service Industries 6
R How to calculate UCL (Upper COntrol Limit) and LCL (Lower Control Limit) Statistical Analysis Tools, Techniques and SPC 5
I want to calculate reliability at 750 hours Reliability Analysis - Predictions, Testing and Standards 8
R How To Calculate & Print CDF and Lower Bound CDF value for some t(time) with Minitab? Using Minitab Software 1
N How to calculate the Premium Freight charges Service Industry Specific Topics 4
A How to calculate Mean and standard deviation without sample size in Minitab Using Minitab Software 5
When do I need to calculate Process OEE? Manufacturing and Related Processes 12
How to calculate Thread Pitch Diameter for non standard TPI like 5/8" 17.75 NF3 Manufacturing and Related Processes 3
C Definition and Way to Calculate some Metrics Lean in Manufacturing and Service Industries 6
M How calculate P value for Linearity and Bias using Excel Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
N Formula that will calculate the NoGo Major Diameter of an M20 x 1.5 6H Thread gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
M How to calculate Cg and Cgk for a 2-Dimensional Area Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
T Calculation Question - Calculate the runner weight for a part Manufacturing and Related Processes 2
M Spreadsheet on How to Calculate SMT Capacity wanted Manufacturing and Related Processes 2
F How to Calculate the unbiased Standard Deviation in Excel using Minitab Formula Capability, Accuracy and Stability - Processes, Machines, etc. 6
S Spreadsheet that will Calculate Audit Duration times based on IAF MD5 and MD11 Excel .xls Spreadsheet Templates and Tools 8
Calculate PPMs by going back to Date of Production or Date Noticed Quality Tools, Improvement and Analysis 7
M How to calculate MTTF (Mean Time to Failure) Reliability Analysis - Predictions, Testing and Standards 1
H How to calculate the Lot Reject Rate Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
L How calculate the number of samples Statistical Analysis Tools, Techniques and SPC 2
A Simple 125 piece part Capabilty Excel .xls sheet to calculate Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 3
S Which one is better to calculate, Cpk or Ppk? Statistical Analysis Tools, Techniques and SPC 11
C How to calculate P value on Probability Plot Statistical Analysis Tools, Techniques and SPC 1
S Supplier Disruption Score and how to calculate it Quality Tools, Improvement and Analysis 4
IAQG OASIS - New tool to calculate Audit Time AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
M How to calculate dimensions of trapezoid ? Quality Tools, Improvement and Analysis 3
How to calculate Surveillance Audit Days in Corporate Audit Scheme IATF 16949 - Automotive Quality Systems Standard 4
S How to calculate Supplier PPM at Receiving Inspection Document Control Systems, Procedures, Forms and Templates 2
How to Calculate Sample Size at 95% Confidence Interval on Surface Roughness Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
R How to calculate the value add time? Lean in Manufacturing and Service Industries 2
G Should I calculate both Cp and Cpk for a Unilateral Tolerance? Statistical Analysis Tools, Techniques and SPC 8