Finish Requirements 2

[KimBellingrath]

I have a drawing submitted to me by a vendor and he has noted the finish as:
"ALL MACHINED SURFACES 125 FINISH OR BETTER"
My question is: Is it always assumed that a smoother finish is 'better' or should the wording be:
"ALL MACHINED SURFACES 125 FINISH OR MORE"
or:
"ALL MACHINED SURFACES 125 FINISH OR LESS"
or:
"ALL MACHINED SURFACES 125 FINISH OR HIGHER"
or:
"ALL MACHINED SURFACES 125 FINISH OR LOWER"

I only want to do this once so it's important that I get it right the first time.
Any suggestions?
Thanks, Kim

 

[ctopher]

"Generally speaking, the ideal finish is the roughest one that will do the job satisfactorily".

http://www.mfg.mtu.edu/cyberman/quality/sfinish/

The note should read "ALL MACHINED SURFACES 125 FINISH".

 

[KimBellingrath]

Thanks for your fast response. The problem I have is that there are times when you WANT something rough and in those cases a 63 or 32 finish would be rejected. So how do I let the vendor (and QC) know that a smoother part would be okay if I don't specify it?

 

[ctopher]

I think maybe use MIN or MAX after finish is the proper term.
Also, after I think about it, depending on the part, I don't think you would want "All machined surfaces...". There may be some surfaces you don't care what finish they are. Maybe "All machined surfaces...except where noted".

 

[drawoh]

KimBellingrath and ctopher,

My understanding, with which my Machinery's Handbook agrees, is that the number attached to the surface finish symbol is the maximum allowable roughness. You have the option of applying two numbers representing the MAX and MIN values for roughness for when you want the surface to be rough.

JHG

 

[KimBellingrath]

drawoh and ctopher,
I agree that's the best way to handle it - thanks both of you. One other thing - the phrase in the notes, according to ANSI is "UNLESS OTHERWISE SPECIFIED..." followed by the note. I've even seen it as "UOS" on Hamilton Standard drawings. The spec says that it should be the first part of the note.
Thanks again,
Kim