Surface Texture - Roughness & Waviness 1

[JustinMEEE]

I am trying to correctly measure the surface roughness of a part I am developing. I do not have a long length over which I can measure, so I am not sure if I am getting accurate measurements. What I need is a handbook (or something similar) that will explain to me how cutoff length relates to maximum roughness values. Unfortunately, my cutof length (& evaluation length) is dictated by the length of my part so I have to accept compromises in the repeatability of my measurements.
I need detailed knowledge of how surface roughness magnitudes relate to evaluation & cutoff lengths so that I can choose the best compromise for my circumstance.
Does anybody know of a handbook or textbook that completely explains surface roughness (height & spacial parameters), waviness, and filter (cutoff) selection?

Thanks,
Justin
Mechanical Engineer
Electrical Engineer

 

[sreid]

Perhaps a place to start.

http://en.wikipedia.org/wiki/Surface_roughness

 

[boo1]

try
ANSI/ASME B46.1
or tutorial at

http://www.nist.gov/calibrations/upload/89-4088.pdf

 

[btrueblood]

The Machinery's Handbook also has a pretty good writeup.

 

[TVP]

Michigan Metrology has some good info on their website:

http://www.michmet.com/texture_parameters_index_by_name.html

 

[tbuelna]

JustinMEEE,

It's good that you want to fully understand the implications of requirements that you specify on your designs. Unfortunately, surface roughness, like so many other inspection requirements, can end up being quite complex. There are various statistical formulas for characterizing the surface micro-profile (RMS, AA, etc.). There are also various topological characteristics to consider, such as perpendicular lay, radial lay, axial lay, etc. And finally, you must consider the dimensional limits over which that surface roughness/profile will actually apply.

On one hand, you want to be quite specific in your specifications, so that what you truly require is made clear. On the other hand, the more specific you make your requirements, the more likely your supplier will end up rejecting marginal parts.

The best thing to do is to get input from your manufacturing source on what they think they can achieve cost-effectively. And then specify that. Basically, make the drawing look like the part.

Good luck.
Terry