How do I properly lable a surface roughness dimension?

[bnmorgan]

I need some advice and clarification about specifying surface roughness and finish.

I've spec'd out a simple Ø.125" pin from 302SS, grand total of 1.750" long, with simple corner breaks to take care of burrs. Along the center of the pin, I put a simple leader and the familiar "checkmark" and 16 in the “elbow” of the check, intending to denote a 16 ?-in finish. No units or anything else. The print has a standard note that all dims are English unless otherwise specified. Now, a producer, a fairly reputable one, has sent a message back asking "is that surface finish 16" or 16mm?"

This scares me.........I don't know if I want parts produced by somebody even capable of fathoming a 16mm RMS surface roughness.....much less 16"....although it'd be an interesting paradox to see on a Ø.125" pin.

My actual question is how I should properly specify a 16 ?-in finish so that nobody gets all confused. The old draftsman here seems to think what I have is proper and sufficient, as does what I can decipher of Machinery's Handbook. I just want to be sure there's a consensus and not something I've overlooked.

Materials department (responsible for the quoting of the parts) thinks I need to do a revision of the print and give some sort of clarifying notes for the convenience of this potential supplier, but it seems unnecessary to clarify something that appears to be an established drafting standard.

All help is appreciated.


SW2007 & NX4

 

[eromlignod]

Your supplier is an idiot. This is an age-old marking and you are doing it correctly. I've used and seen these markings for years and years. If he sees a check mark with a 16 in it, he should know immediately what you meant. It's a very common mark and it's intuitively obvious what you meant.

I'm guessing he wants to know if it's micro-inches or microns. But if he used his head, he'd know that 16 microns would be basically the finish you'd get from cutting with an oxy-acetylene torch.

It might be his smart-ass way of telling you that he thinks that a 16 u-in finish is too fine. That is pretty fine and would have to be ground or very-finely sanded on a lathe, but it's not a big deal. I believe standard machine dowel pins come with at least that fine a finish.

Don
Kansas City

 

[KENAT]

What you have should be OK.

We have an overal finish note "SURFACE ROUGHNESS TO BE ____ RMS PER ASME B46.1. " and then any surfaces with a different roughness have their own callout using the symbol.

You could always reference the ASME standard to cover yourself, in fact I'd be tempted to recomend it.

Many will argue that you don't need to reference the relevant standard on the drawing and that general industry practices are adequate etc but then you hit a situation like yours.

If you'd referenced the ASME standard there'd be less chance of misunderstanding.

 

[btrueblood]

Better is to call out "Interpret drawing per ASME Y14.5 1994"; this document includes by reference everything from threads (B18) and surface finishes to GD&T and drawing line and note interpretations (14.1, 14.2, etc.).

 

[KENAT]

Our first note is usually a ref to 14.5, however where we call upon a specific standard we normally specifically reference them.

14.5 doesn't always lead directly to all the other related standards, Y14.100 is a bit better but still you're relying on the person reading the drawing to be familiar with the standars.

If you explicitly state the relevent industry standard for each aspect you're reducing the chance of error.