Surface Roughness General Coverage Specification
Surface Roughness General Coverage Specification
(OP)
Our notes are headed:
We have a general surface roughness note the value of which gets set as appropriate for each drawing. (I've just added the italics here for clarity - they aren't on drawings.)
We've been using this note since 2005, always believing it to be clear that it was a maximum roughness value, and I don't think we've ever had machine shops complain or be unclear on this. We don't use the symbol as part of the note because these notes are done in an inserted Word document as the text editing abilities of our CAD software are a bit weak and it would be time consuming/error prone to manually position the symbol etc.
We apparently have a new shop as part of a vendor consolidation effort (replacing several smaller previous suppliers) and they seem to be confused by this.
On one print where I'd separately indicated a certain bore to have min & max roughness requirements (125-250) using standard symbol they actually asked for then general roughness to be reduced to 63 Ra from 125. I debated this with purchasing but eventually gave in making some allowance for my (125-250) call-out perhaps being a bit unusual and causing confusion.
However, now they are asking for me to change another print where I have 125 in the general notes and no weird 'minimum roughness' call outs on the drawing. I'm refusing to tighten the roughness for no functional reason (another shop made this part previously with no issues) but have added 'MAX' after the value just to clarify.
I've looked in Global & Genium DRM's but don't see any mention without the symbol and I don't have B46.1. Machinery's does say "It is considered good practice to always specify some maximum value, either specifically or by default" but doesn't really say if a value given in a note is assumed to be maximum.
So to the questions
Q1: Per B46.1 does our standard note clearly specify maximum roughness, or because we aren't using the standard symbol do we need to explicitly say 'MAX' to clarify?
Q2: Am I right to be concerned about how good this shop is if this note that we've been using for years is causing this much confusion and they're actually asking me to tighten requirements?
Thanks,
Quote:
NOTES: UNLESS OTHERWISE SPECIFIED
We have a general surface roughness note the value of which gets set as appropriate for each drawing. (I've just added the italics here for clarity - they aren't on drawings.)
Quote:
SURFACE ROUGHNESS SHALL BE 125 Ra PER ASME B46.1.
We've been using this note since 2005, always believing it to be clear that it was a maximum roughness value, and I don't think we've ever had machine shops complain or be unclear on this. We don't use the symbol as part of the note because these notes are done in an inserted Word document as the text editing abilities of our CAD software are a bit weak and it would be time consuming/error prone to manually position the symbol etc.
We apparently have a new shop as part of a vendor consolidation effort (replacing several smaller previous suppliers) and they seem to be confused by this.
On one print where I'd separately indicated a certain bore to have min & max roughness requirements (125-250) using standard symbol they actually asked for then general roughness to be reduced to 63 Ra from 125. I debated this with purchasing but eventually gave in making some allowance for my (125-250) call-out perhaps being a bit unusual and causing confusion.
However, now they are asking for me to change another print where I have 125 in the general notes and no weird 'minimum roughness' call outs on the drawing. I'm refusing to tighten the roughness for no functional reason (another shop made this part previously with no issues) but have added 'MAX' after the value just to clarify.
I've looked in Global & Genium DRM's but don't see any mention without the symbol and I don't have B46.1. Machinery's does say "It is considered good practice to always specify some maximum value, either specifically or by default" but doesn't really say if a value given in a note is assumed to be maximum.
So to the questions
Q1: Per B46.1 does our standard note clearly specify maximum roughness, or because we aren't using the standard symbol do we need to explicitly say 'MAX' to clarify?
Q2: Am I right to be concerned about how good this shop is if this note that we've been using for years is causing this much confusion and they're actually asking me to tighten requirements?
Thanks,
Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?





RE: Surface Roughness General Coverage Specification
So if you mean Max state Max.
Shop might be on the ball. They might be thinking "the process I'm going to use will leave a much smoother surface. Do they really want a secondary operation to make it rough? "
RE: Surface Roughness General Coverage Specification
It may be purchasing muddling things up, and could be that the shop is actually more competent than anyone else we've used. I asked if they wanted me to speak to the shop and they didn't, whatever.
Thing is on the first drawing, I changed the value to 63 from 125, didn't add 'MAX' and got copied on an email from then vendor where they said they liked it, which is what's making me think it may not just be purchasing.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
RE: Surface Roughness General Coverage Specification
If you, as the designer, can live with a rougher surface then that is the appropriate value to put on the drawing. The supplier may be playing a game to get the spec updated to their typical capabilities which may be tighter than most other shops, thus effectively limiting their competition.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Surface Roughness General Coverage Specification
The thing that makes me doubt the 'knowledgeable supplier' part is that they were happy when I changed it to '63' from '125' on the first print without adding MAX.
As to your theory about tightening specs to limit competition, I'm pretty sure we already have one other shop that does this, so it's definitely possible.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
Personally I like dealing with small shops on a personal level; I get the best out of them, and we both know where we stand. Lots of tales from the trenches I could share over a pint/shot some day.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Surface Roughness General Coverage Specification
"The specification of only one [roughness average] rating shall indicate the maximum value and any lesser value shall be acceptable."
RE: Surface Roughness General Coverage Specification
RE: Surface Roughness General Coverage Specification
Frank
RE: Surface Roughness General Coverage Specification
For reasons mentioned above we state ours in note form without the symbol.
Thanks for looking though.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
However, I don't think that has anything to do with the issue. A single surface roughness value is always an upper limit. I would stay away from using "max" in this case because Rmax is another surface finish parameter that is completely different from Ra. Stating Ra max. is just redundant and confusing.
----------------------------------------
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 Roughness General Coverage Specification
I'll hold off changing our standard note for now, as based on this thread (and the vendor) it appears there's room for doubt but that just saying 'max' could also confuse.
On the print I just sent out I manually overlaid the symbol on the notes just to be sure!
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
See this form: h
I also do not use "surface finish". It can lead to confusion as a final finish such as paint, etc. Another topic...
Chris
SolidWorks 11
ctopher's home
SolidWorks Legion
RE: Surface Roughness General Coverage Specification
h
(although on quick read it doesn't answer the question asked here)
RE: Surface Roughness General Coverage Specification
That is if using the symbol, then if a single value is stated that is the max Ra roughness.
Sadly it doesn't say anything about use of the term in text.
(Funnily enough, our sister site makes the measurement equipment they talk about & we make the AFM they mention around page 99. So you might think we'd be experts but apparently not on the specification aspect!)
Chris - that's why the note says 'surface roughness'
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
"The allowed value of surface roughness .... can be specified either as a maximum value, which may not be exceeded, or as a range of values ...."
So a single value is always an upper limit (with zero as a lower limit since negative values are impossible). I don't think the presence of a surface roughness symbol is necessary if you spell out surface roughness. Symbols are just a convenient shorthand for when you don't want to explicitly write things in text.
----------------------------------------
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 Roughness General Coverage Specification
Using the symbol, "Ra MAX" is the default with a single value; an absolute or range of Ra values can be specified as needed.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Surface Roughness General Coverage Specification
I agree.
Chris
SolidWorks 11
ctopher's home
SolidWorks Legion
RE: Surface Roughness General Coverage Specification
RE: Surface Roughness General Coverage Specification
RE: Surface Roughness General Coverage Specification
RE: Surface Roughness General Coverage Specification
ASME Y14.36 para 4.3 "Roughness Average (Ra)" states "The principle parameter specified for roughness average, Ra, defined in ASME B46.1. It is the value shown in position "a" of the surface texture symbol (i.e. directly above the V of the surface texture symbol)."
Also Figure 5 of ASME Y14.36, which shows samples of surface texture symbols staes in the primary example that "The specification of only one rating for roughness average shall indicate the maximum value, and any lesser value shall be acceptable."
For this reason, in accordance with the standard, maximum roughness average the interpretation, and adding the word MAXIMUM to the drawing only muddies the waters, IMHO. Note that ASME Y14.36 SURFACE TEXTURE SYMBOLS, is specified in ASME B46.1 as the drawing standard for surface texture symbology. Having a copy of B46.1 is probably not necesary, but you should get a copy of the 8 page ASME Y14.36 if you can.
RE: Surface Roughness General Coverage Specification
My issue is just that it's difficult/error prone to have the roughness symbol embedded in my general notes the way we do them.
So then we just have the text statement per my OP.
However, it seems the relevant ASME std only talks about the value in context of the symbol.
When I remember I've been changing the note to:
I haven't had any more complaints, but I'm hesitant to change the default template in case it does get some other vendors confused between Ra & Rmax. Given I explicitly state 'Ra' and the 'Max' is in parenthesis I'd sure hope not but then I wouldn't have expected any machine shop to complain about the note as is so...
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
RE: Surface Roughness General Coverage Specification
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Surface Roughness General Coverage Specification
Nice to be back. A former client dragged this old job shopper out of retirement and brought him back to check again, for a while. We may be a dying breed, but not just yet.
RE: Surface Roughness General Coverage Specification
I'm not really checking anymore though (since Jon got let go in 2009) so I guess I get to go back to the dark side!
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?