Flatness - Rectangular part using the three jack method

#1
I have always used the three screw method of flatness measurement. I encountered a rectangular part which using the three jack method displayed a flatness .105.

Upon attempting to reject this as it was grossly OOT, I received instruction to try a different method which seemed like a problem to me as I believe the three jack method to be tried, true, and definitive. The suggestion was to place the part on four jacks. One on each corner. Adjust until two opposing corners are at the same height. Then make the other set of corners the same height. So top left and bottom right are now the same height and I have zeroed my height gauge on them and the other two opposing corners are both .038 higher than the two 0 corners. Upon scanning with the height gauge I measured a flatness of .055. The parts are still OOT, but they are profoundly better as the surface now fits in a smaller zone. I don't know if I should accept this method. Is there a fundamental flaw that I am just not seeing? Any feed back would be appreciated.
 
Elsmar Forum Sponsor

Jim Wynne

Staff member
Admin
#2
Try setting the part on 1-2-3 blocks with the target surface facing the surface plate, then check the part with the height gage from underneath.
 
#3
That is just not how it is done. I have seen you reply similarly to an old thread on this site and what you are checking by doing that is parallelism. You have to use adjustable jack stands to remove any influence of the opposing surface's relationship with any point of contact. And you measure the surface face up. Not down. The three jack method is not in question here. I am only looking for insight to a fourth jack.
 

Jim Wynne

Staff member
Admin
#4
That is just not how it is done. I have seen you reply similarly to an old thread on this site and what you are checking by doing that is parallelism. You have to use adjustable jack stands to remove any influence of the opposing surface's relationship with any point of contact. And you measure the surface face up. Not down. The three jack method is not in question here. I am only looking for insight to a fourth jack.
The idea is to isolate the target plane, and the method I proposed will do that. I know the difference between flatness and a parallelism. There is no influence from the opposite surface. If you were to put the part on blocks with the target plane facing up and then draw the height gage across it, that would be checking parallelism.
 
#5
The blocks are parallel to the surface plate. If you rest the surface you are trying to measure on the blocks your surface will be then be subjected to the influence of its potential irregularities which also will not be able to be measured now because you have a 123 block in the way.
 

Jim Wynne

Staff member
Admin
#6
The blocks are parallel to the surface plate. If you rest the surface you are trying to measure on the blocks your surface will be then be subjected to the influence of its potential irregularities which also will not be able to be measured now because you have a 123 block in the way.
I understand the bit about the blocks being in the way of measuring the entire surface. I also understand about the blocks resting on the surface plate, but jacks have to rest on the plate as well. Never mind.
 

Proud Liberal

Quite Involved in Discussions
#10
Since flatness is defined as the smallest distance between 2 parallel planes that will enclose all points on a surface, be aware that anything short a a full 3-D vision scan of the surface will ALWAYS be an estimate of flatness and as such one can only claim that "the flatness is no worse than .XXX". If changing your setup or technique yields a lower value, use the lowest value you can obtain. But you can still only claim a "no worse than" result.
 
Thread starter Similar threads Forum Replies Date
hogheavenfarm GDT Flatness measurement question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 10
F Flatness VS parallelism Design and Development of Products and Processes 6
B How to do a control chart - Machining product that requires flatness control Capability, Accuracy and Stability - Processes, Machines, etc. 1
S Difference between Surface Finish (Ra) and Flatness (GD&T) Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
G From an ISO 17025 auditor perspective must micrometer calibration check anvil flatness? General Measurement Device and Calibration Topics 4
N Do I need to approach galvanized steel sheet flatness issue with DOE? Problem Solving, Root Cause Fault and Failure Analysis 9
G How to compute or estimate a micrometer or caliper flatness using optical flat General Measurement Device and Calibration Topics 2
W Standard for Micrometer Anvil Flatness Oil and Gas Industry Standards and Regulations 5
G Caliper or Micrometer's Dimensional Flatness General Measurement Device and Calibration Topics 5
C Flatness Measurement Errors from a Datum - Test Method General Measurement Device and Calibration Topics 3
P Checking flatness with Go and No Go Jig Manufacturing and Related Processes 2
J Flatness measured to locations of a plane Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
B Result of a Flatness MSA on a CMM Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
C Measuring Flatness of a Pump Cover General Measurement Device and Calibration Topics 14
N The right method to Measure and Evaluate a Flatness Callout Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
F Reason a plane would have a runout applied and not a flatness callout Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
E Flatness Measurement of Plastic Molded Parts - Clamping / Holding Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
C Micrometer Parallelism and Flatness Calibration Requirements and Specs General Measurement Device and Calibration Topics 10
G Determining flatness and parallelism rapidly Manufacturing and Related Processes 2
Q Micrometers to Measure Coating Thickness - Failed Calibration Flatness & Parallelism General Measurement Device and Calibration Topics 9
optomist1 GD&T Flatness Automatic Indirect Control Rule #1 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 20
B Flatness Call Out confusing me - What they are wanting and how to check it? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 42
C Surface Plate Calibration - How to verify the flatness of a granite surface plate General Measurement Device and Calibration Topics 1
A Ovality and Flatness generated after Heat Treatment of Rolled Rings Manufacturing and Related Processes 3
B Inspection Tools for Flatness and Channel Depth of Bipolar Fuel Cell Plates Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
C Techniques for Measuring Flatness General Measurement Device and Calibration Topics 37
Z Inspection of Flatness of a part using an electronic device Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
W Warping / Flatness SPC - X bar-R chart - Control is Max 0.15 Statistical Analysis Tools, Techniques and SPC 5
D Flatness tolerances for tempered cold rolled stainless steel coils Manufacturing and Related Processes 3
Proud Liberal Flatness / Straightness / Bow specification Various Other Specifications, Standards, and related Requirements 12
D Optical flats - "FLATNESS INTERPRETATION CHART, Light Wave Band Pattern Guide" General Measurement Device and Calibration Topics 4
D Looking for 100% sort testing equipment for overall length, flatness, and parallelism General Measurement Device and Calibration Topics 1
S What is the best method for checking the flatness of a flexible part? General Measurement Device and Calibration Topics 4
G Uncertainty Experts - ISO 17025 - If the Distribution is Rectangular Measurement Uncertainty (MU) 2
B Treating Resolution - Rectangular or Triangular Distribution Measurement Uncertainty (MU) 6
J Blueprint Note: Rectangular Distribution is Permissible - Concentricity of Two Holes Capability, Accuracy and Stability - Processes, Machines, etc. 5
W MU - Type B estimation - Which distribution to use? Triangle? Rectangular? General Measurement Device and Calibration Topics 3
D Partial FAI - AS9102 -One single drawing has 10 part numbers AS9100, IAQG 9100, Nadcap and related Aerospace Standards and Requirements 2
A 21 CFR Part 11 - Steps to take if we want to validate an electronic system Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 2
T ISO 13485 8.3 - Non-Conforming Materials - on-line rework or part of process? ISO 13485:2016 - Medical Device Quality Management Systems 11
DuncanGibbons Should the requirements FAA/EASA Part 21 be addressed within the QMS and AS9100D quality manual? AS9100, IAQG 9100, Nadcap and related Aerospace Standards and Requirements 5
K IEC 62304 compliance - Code reviews as part of verification strategy IEC 62304 - Medical Device Software Life Cycle Processes 5
G Gage R&R - Where am I going wrong? Part of a FAIR submission (Aerospace) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
A 21 CFR part 11 - section 11.100 - Electronic Signature Certification Other US Medical Device Regulations 6
M AS9102B Detail Part/Assembly FAI Form 1 box 13; AS9100, IAQG 9100, Nadcap and related Aerospace Standards and Requirements 2
M 2xMOPP insulation for Applied Part B. IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
A ISO 41001:2018 - Clause No.8 Operations Part Quality Management System (QMS) Manuals 2
NDesouza Getting Rid of Part Marking Errors Benchmarking 39
L Wearables 21 CFR Part 11 compliance Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 1
DuncanGibbons How are part cut out specimens made and tested? Manufacturing and Related Processes 1
Similar threads


















































Top Bottom