Finish vs. roughness 1

[Tenkan]

On some of my drawings that do not require a finish, I've left the default note "NONE"... this has led to some questions despite the roughness Ra value in the general tolerance block. As if the two callouts contradict each other.... ?

So help me understand finish callouts. I’m not a machinist, but I always thought a machinist would look at the surface roughness callout and adjust his setup accordingly! Is this correct? What are the steps in machining a part to a desired surface roughness, say 32 or 125µin? So why would you call that roughness, a finish?

lightweight, cheap, strong... pick 2

 

[KENAT]

From a colloquial point of view, the word 'finish' is sometimes used to refer to the surface roughness of the finished part.

From a drawing point of view finish usually means plating/treatment etc.

How to make sure this doesn't get misunderstood I'm not sure, could it be as simple as striking through the finish box rather than stating none?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MikeHalloran]

"Finish" normally includes paint, or chrome plate, or if "none", rust.

"Roughness" is a measure of surface asperities. Sometimes the term "microfinish" is used. If a lower number is specified, a machinist will reduce the transverse feedrate.



Mike Halloran
Pembroke Pines, FL, USA

 

[powerhound]

I don't know how it got started but KENAT is right. Sometimes surface roughness and surface finish are used interchangably in machine shops. I know that doesn't make it right. Especially since there really is no such thing as NONE surface roughness. It would seem to only make sense that you are referring to a plating or anodizing process but some folks just don't make the connection. I have not seen many prints with a general note saying there is no finish. In my experience if no finish is required then it isn't even mentioned. I guess the general note is part of a drawing template that forces you to input something so it isn't inadvertently left off.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Vimalmechs]

Hi Koda,

No.finishing process like passivation, anodization, epoxy coating, cleaning etc comes under finish.

Suppose you just want to machine an AL6061T6 block. and you are not at all concerned with the surface finish. Then the part will be having its stock finish or the finish based on your method of manufacturing process.As like general sheet tolerances there should be a separate column for surface finish and finish.
In finish column, indication will be none. surface finish General surface finish value will be indicated.

To achieve your desired surface finish & Lay. The machining process will vary and as well there could be additional process like Hand polishing, buffing etc, after machining.

Suppose you are designing cylindrical part with a sealing surface with 32µin, circular lay. u should go for CNC LATHE turning to achieve the surface and lay direction.

Hope i am clarified you.
Regards
Vimal VV

 

[Tenkan]

Thanks everyone for the replies, I see now that it is a colloquial term used. What I've decided to do is delete the finishNONE note all together on parts that do not require a finish at all. Since the term is colloquial, right or wrong I'm not going to win any argument.



lightweight, cheap, strong... pick 2

 

[UchidaDS]

If I have a part that is come out, let's say from sheetmetal or quartz or other process rather than the machine shop. And at the bottom of the drawing block there is a symbol of 63 v-- finish.
My understanding is that is the maximum or better (smoother) roughness/finish to be achieved for the final product. Meaning that no grit blast (to make it close to 63Ra) or polishing (to make it smoother) required for the second operation. Is that valid?
If it is maximum or better, is there any tolerance apply to this?

 

[ctopher]

There was a discussion last year.
thread1103-318284


Chris
SolidWorks 13
ctopher's home
SolidWorks Legion

 

[dgallup]

Surface roughness is always a maximum unless an upper and lower limit are specified, then the value has to fall within the given range. There are three surface roughness symbols, one requires material removal to achieve it, one prohibits material removal to achieve it and the third is agnostic. Assuming you have the far more common agnostic surface roughness with only an upper limit then nothing is required as long as the roughness is below the limit.

----------------------------------------

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.

 

[UchidaDS]

Thanks dgallup!
That help me to be more certain about this.

 

[Tenkan]

What’s interesting is that Wikipedia’s article defines Surface Finish to include Surface Roughness as a component of Surface Finish. Within this context it seems more in line with typical drafting finish callouts excluding secondary surface operations such as paint, polishing, plating etc. which I normally thought of as a “finish” and where roughness included lay and waviness…

Is it just me, or is the Wikipedia article opposite what we see from a drafting point of view?

[URL unfurl="true"]http://en.wikipedia.org/wiki/Surface_finish[/url]

lightweight, cheap, strong... pick 2

 

[dgallup]

I think the distinction is between "FINISH" meaning a coating, plating, etc. and "SURFACE FINISH" meaning texture, roughness, lay, etc.

----------------------------------------

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.

 

[Belanger]

Koda -- that's how I've always looked at it. Surface finish is a general term that includes roughness, waviness, and other parameters. We can't think of finish as synonymous with roughness.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems