a question about surface roughness

From: F. L. (fl200240@hotmail.com)
Date: Sun Mar 24 2002 - 06:25:44 EET

Deal All,
    I am working on a kind of rapid prototyping technique and want to
comapre the surface roughness of parts fabricated by our machine with those
by other RP machines. We have a portable surface roughness gage in our lab
so it is very easy to test Ra with the unit of micrometer. But for certain
other RP parts, we can only find Ra value with the unit of microinch from
the literatures. Do you think we can simply covert microinch into micrometer
with the following relation:1 micrometer = 40 microinch? I read a paper
before, the author listed both micrometer and microinch in a table for the
same part in their paper. that is why i am a little confused here. If we can
convert the unit directly, why the author listed both of them. And also I
want to know the relation between the RMS and Ra.
I know the questions seem silly. please tell me something about this. Thanks
a lot.


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