Surface Finish

[rapper]

Does anybody know the appropriate 'profile of surface' tolerance to achieve a surface accuracy of 0.25mm RMS.

 

[costast]

i imagine you mean 0.25 microns RMA and not .25 mm ?

you dont say if your part is round or flat. Normaly 0.25 can be acheeved by fine grinding or superfinishing.

 

[rapper]

Thanks for the reply, a little more background - the part is a 2.5mm thk aluminium curved forming which is a segment of an antenna reflector.

Our customer requires a 0.25mm RMS surface accuracy - the accuracy an antenna assembly is measured by probing approx 500 points and calculating an RMS error.

The reason for the query is that i am trying to equate the RMS value to a 'profile of surface' geometric tolerance to pass on to our toolmaker for machining the form tool surface.

 

[marekmb]

If you still need help with RMS, I think RMS (Root Mean Square) Error- math. formula to describe error from ideal surface at measured points. put in google rms error to find out more

 

[kens356sc]

A .25mm RMS (Root Mean Square) accuracy of the ideal profile is calculated from a formula in Machinery Handbook (surface texture, RMS in the index). I would think your coordinate measuring machine would be able to do this automatically, but the formula is:

RMS Avg. = sq. rt. of ((Ya2 + Yb2 + Yn2)/n)

(the 2 means squared)

The AA average is similar, but does not square the readings and square root the average.