Surface finish (Evaluation Length)

Kostas M

Starting to get Involved
#1
Hello Everyone,

I need your help regarding the parameters that I need to choose for measuring the surface finish on an inside diameter.

The length that the finish needs to be maintained is 12mm and the requirement is Rz5. According to the spec for Rz5 the cut-off length has to be 0.8mm.,
My question is the evaluation length. How many cut-off lengths do I have to use? If the length that the finish needs to measured is 9.6 mm and the cut-off length 0.8, do I have to use 12 cut-off length? (9.6/0.8=12)
I have found a lot of tables that specify for 0.8 cut-off length, the evaluation length have to be 4mm which means 5 cut-off lengths.

Thank for your assistance in advance
Kostas
 
Elsmar Forum Sponsor

Jen Kirley

Quality and Auditing Expert
Leader
Admin
#2
Hello Everyone,

I need your help regarding the parameters that I need to choose for measuring the surface finish on an inside diameter.

The length that the finish needs to be maintained is 12mm and the requirement is Rz5. According to the spec for Rz5 the cut-off length has to be 0.8mm.,
My question is the evaluation length. How many cut-off lengths do I have to use? If the length that the finish needs to measured is 9.6 mm and the cut-off length 0.8, do I have to use 12 cut-off length? (9.6/0.8=12)
I have found a lot of tables that specify for 0.8 cut-off length, the evaluation length have to be 4mm which means 5 cut-off lengths.

Thank for your assistance in advance
Kostas
Hello Kostas, I am sorry for the delay in this response.

I don't want to over-complicate the method for inspection when the requirement seems simple: the surface will have a finish of x.

Finish is usually measured with a profilometer, so I welcome any and all Covers to add their expertise because I am not aware of cutoff unless it is concerng an area to which the finish requirement does not apply. A profilometer will send a stylus along a length determined necessary for that instrument to calculate roughness detected over that distance. It is my understanding that any and all surface identified by specification as requiring this R value would be able to fall into this kind of measurement.

Do I understand your question correctly?
 

Miner

Forum Moderator
Leader
Admin
#3
Kostas,

Let's look at the reason for the various lengths:
  • Cutoff length - this is used to separate roughness (Rz) from waviness. Too large a cutoff, and you start measuring waviness instead of roughness.
  • Evaluation length - this is set up as multiples of the cutoff length to allow averaging of multiple roughness measurements to minimize measurement variation. Five is a common default number used for averaging, but is not a definitive requirement. As Jen said, you do need to control Rz on the entire surface, so there is no reason you cannot specify the evaluation length to be 12x the cutoff length. The point is that this now becomes a business decision on your part to minimize risk. You are in control of this.
 

Kostas M

Starting to get Involved
#4
Hello Mike and Jen,

Thank you very much for your answers.

I did my research and found the ISO 4288 spec for Surface texture: Profile method -Terms, definitions and surface texture
parameters.
Since the Rz is the average of the peak to the valley differences of the cut off lengths, if you use more cut-off lengths and there is just a area with bad finish on the surface the reading will be lower. If you measure the finish only on the rough area using less cut-off lengths, the reading will be higher.
According to the table of the spec, depends on the call-out of the drawing, you set the parameters on the profilometer. The table shows that there is a limit. For example if the specification is Rz 5, you need to use cut-off length 0.8mm X 5 (Total 5 cut off lengths) in order for the evaluation length to be 4mm.

Thanks
Kostas


1613421904426.png
 
Thread starter Similar threads Forum Replies Date
Ron Rompen Surface Finish Correlation between Ra, Rz and Tp (bearing surface ratio) General Measurement Device and Calibration Topics 3
J Gear Surface Finish - Print with the word "calibrated" Manufacturing and Related Processes 2
8 Surface Finish - Callout as 8 - 16 Rq Manufacturing and Related Processes 1
GoKats78 Callout on Surface Finish General Measurement Device and Calibration Topics 12
S Difference between Surface Finish (Ra) and Flatness (GD&T) Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
Proud Liberal Surface finish measurement (roughness) - Rz under the ISO standard vs ANSI standard Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
Proud Liberal Measuring axial and radial surface finish (16 Rz) on a broached internal radius Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
B Surface Finish Equipment MSA (Measurement System Analysis) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
kedarg6500 Surface Finish Measurement Methods Inspection, Prints (Drawings), Testing, Sampling and Related Topics 13
P Surface Finish measurement for machined (finished) component/part Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
J Definition Standards for Dimensions and Surface Finish on a Rod Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 11
A Is it mandatory to have a profilometer to inspect >16 surface finish? General Measurement Device and Calibration Topics 8
T Interpretation of Surface Finish Specification Manufacturing and Related Processes 2
D Surface Finish Inspection Company (Laboratory) (Detroit area) needed Manufacturing and Related Processes 1
A Conducting a DOE in Minitab - Improving Surface Finish of an Impeller Using Minitab Software 10
N PCB (medical device) Surface Finish Selection. Manufacturing and Related Processes 2
S Surface Finish - Conversion factor to transform Rz Jis in Rz Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
N MSA (Measurement Systems Analysis) for Surface Finish Equipment Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
P Inner Diameter Surface Finish Ra Value vs. Surface Finish Graph Output Manufacturing and Related Processes 11
ScottK Inspecting surface finish on SS on a piece that can't be measured with current equip. Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
ScottK Surface Finish on machined brass (or other metals)- Attribute or Variable inspection? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
ScottK Measuring Capability on a One Sided Variable (Surface Finish) Capability, Accuracy and Stability - Processes, Machines, etc. 17
W Surface Finish parameters - Mechanical stylus based testing of a cylindrical part Manufacturing and Related Processes 2
W Surface Finish Measurement Technique Manufacturing and Related Processes 3
T Surface Finish Requirements (Ra 150) for Blasted Titanium Surfaces Manufacturing and Related Processes 12
J Surface Finish Tester Recommendations with both Ra and Rz (english and metric) scales Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
Ron Rompen Conversion of surface finish measurements Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
U How to do Gage R&Rs on Surface Finish Gages Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
Geoff Cotton Surface Finish - G5 - Where is this from and how can I measure it? Manufacturing and Related Processes 6
Marc Surface Finish Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
J The best way to define a surface finish General Measurement Device and Calibration Topics 1
J Surface Finish - What is the meaning of the term ?LAY?? Coffee Break and Water Cooler Discussions 4
D Air Gauging: Are the results affected by surface finish of the bore? General Measurement Device and Calibration Topics 1
H Regarding external surface temperature limit requirement for lab incubators. CE Marking (Conformité Européene) / CB Scheme 2
DuncanGibbons Typical Surface Roughness Requirements for Aviation AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
I Good Surface Plate Suppliers? General Measurement Device and Calibration Topics 1
T Capability calculation of surface profile Capability, Accuracy and Stability - Processes, Machines, etc. 20
S Alcohol based cleaner for Food Contact Surface? Food Safety - ISO 22000, HACCP (21 CFR 120) 0
V EN ISO 10993-1, Category of surface device by nature of body contact Other Medical Device Related Standards 2
W Surface Profile All-Around AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
T Is there a direct relation between surface roughness and gloss? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
D CED Coating in Cast iron surface Reliability Analysis - Predictions, Testing and Standards 0
S Surface roughness Rz Manufacturing and Related Processes 1
L GD&T Position for surface Inspection, Prints (Drawings), Testing, Sampling and Related Topics 9
P Surface scratch measurement General Measurement Device and Calibration Topics 1
D Surface Roughness understanding Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
D Calibration of Digital thermometer with surface probe General Measurement Device and Calibration Topics 1
R Design and Manufacture Guidelines for Surface Mount Technology Misc. Quality Assurance and Business Systems Related Topics 9
M Active Surface Disinfectant Claims - FDA vs EPA and Hands vs Objects Other Medical Device and Orthopedic Related Topics 0
P Gas Nitriding Surface Hardening of Stainless Steel 304 ISO 13485:2016 - Medical Device Quality Management Systems 4

Similar threads

Top Bottom