What is "Cut off Length" in Surface roughness tester

[psavijay]

Could anybody explain What is Cut off Length in Surface roughness testing instruments and what is it's effect on measurement with respect to various cut off lengths

 

[Jim Wynne]

Cutoff length refers to the distance a profilometer stylus travels across a surface when taking a measurement. In general, the shortest distance that provides uniform results is best.

 

[Claes Gefvenberg]

and what is it's effect on measurement with respect to various cut off lengths

You can find advice on how to choose cut-off length in ISO 4288, Geometrical Product Specifications (GPS) -- Surface texture: Profile method -- Rules and procedures for the assessment of surface texture.

Usually, an evaluation length equal to five consecutive cut-off lenghts provides a good result.

/Claes

 

[psavijay]

Hi

thanks Now I understand Cut off length is equal to a sampling length and Evaluation length is equal to n*sampling length.
I am happened to use Mitutoyo SJ 400 and finally I got the user manual

 

[Claes Gefvenberg]

Now I understand Cut off length is equal to a sampling length and Evaluation length is equal to n*sampling length.
I am happened to use Mitutoyo SJ 400 and finally I got the user manual

Great. I always find it commendable when people find out about the inner workings of the equipment they use instead of just running it and accepting the output.

/Claes

 

[Jeff Chang]

Hi
But if samples surface length not enough or very close to 5~6x cut off length to be measured 5*cut off length.
Can I get result from short cut off length? how short?

Another quesiton: the measured probe moving direction is red arrow or blue arrow in attached which one is incorrect direction of measuring.

For my understanding, according to DIN EN ISO 4287 the blue measuring direction is incorrect. Am I right?

 

[dgriffith]

I agree with red. If the tooling marks are parallel to the edge, you'd want to know the roughness of the surface, which is the combination of the peaks and valleys, yes?. If you drag the stylus parallel to the marks, which may actually be grooves, it might be smooth, but you're only measuring one valley.
The red direction drags the stylus across the peaks and valleys and is better indication of roughness/smoothness.

 

[Claes Gefvenberg]

Ok, here's a late reply Beware of getting surface defects (for instance scratches) mixed up with surface roughness (which is indeed the profile - peaks and valleys, but not surface defects).