Surface finish specifications
Surface finish specifications
(OP)
I have been drawing a machined part based on previous designs and one area requires an Ra1.6 surface finish. However the Engineer checking the job has found another drawing which specifies the same area finished to Ra1.2. Having never had cause to give it much thought I have always assumed that the Ra range was specified in the following steps Ra 0.4, 0.8, 1.6, 3.2 and so on. Having looked into it a little I take it you can define whatever finish the job really needs - fair enough. My question is what is the standard range based on and why are those partiular values used?
In this case I suspect the change is just an error copied from one job to another.
In this case I suspect the change is just an error copied from one job to another.





RE: Surface finish specifications
Roughness sampling lengths, on the other hand, can only be a small number of values. 0.8 is the default if you do not specify it.
I don't know who/how the standards were determined but I keep a list of them stuck on the wall for reference.
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Surface finish specifications
Ra in µin: 2000, 1000, 500, 250, 125, 63, 32...
Ra in µm: 50, 25, 12.5, 6.3, 3.2, 1.6, 0.8...
RE: Surface finish specifications
1000 (25.2) = sand casting, torch or saw cut
500 (12.5) = rough filing, disk grinding, heavy cut and coarse feed on mill or lathe
250 (6.3) = forging, extrusion, permanent mold castings
etc. http://www.engineershandbook.com/Tables/surfacerou...
RE: Surface finish specifications