runout used on rotating parts only? 3

[bxbzq]

I don't see the standard states a runout can only be used on a rotating part. But to verify it, you need to rotate it around an axis and read the errors from a dial indicator running through the part's surface. We say inspecting a part is a process of simulating part's function or assembly. We also say a well drafted drawing tells how the part works. So if a part does not rotate, why would anyone put runout control on the drawing? I've always seen drawings of stationary parts have runout control on it's cylinder surface or surface perpendicular to the datum axis. I think it's legal, but is it really good practice?

 

[CheckerHater]

Let say, you have to make a piston for hydraulic cylinder.
Piston does not rotate. Why use lathe to make it?

 

[bxbzq]

I don't follow you. You are talking about manufacturing while I'm talking about function and inspection.
Why use lathe to make it? Because it's the easiest way to meet functional requirement, capable of holding tight tolerance at relatively low cost.
Are you saying a piston is lathed therefore it is defined by runout on its drawing?

 

[CheckerHater]

I am saying, the answer to both questions is “BECAUSE IT’S THE BEST TOOL FOR THE JOB”

 

[JMarv]

Because it's the easiest way to meet functional requirement

I think you pretty much answered your own question. Runout is often used as an alternative to concentricity "because it's the easiest way to meet functional requirement."

Joe
SW Premium 2012 SP3.0
Dell T3500 Xeon W3505 2.4Ghz
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ATI FirePro V5800

 

[CheckerHater]

Not only Runout is simple, inexpensive, well understood on the shop floor, but it is virtually the most powerful control.

I am sure someone else may explain it much better than I ever will. Please take a look at the following Newsletter:

http://www.mechsigma.com/newsletters/2003_10_Newsletter.pdf

 

[TheTick]

Runout is unique in GD&T because it actually prescribes a specific method to measure.

 

[pmarc]

I will try to express what CH said in a different way.

From purely geometrical point of view runout is a very powerful composite control - it simultaneously controls location and orientation of the feature to the datum axis (if we are talking about a cylinder) and its form (circularity or cylindricity depending on the type of runout control). This is pretty a lot in one.

From inspection point of view it offers even more - being able to verify so many characteristics in single set-up is really beneficial. Form controls, as separate callouts, can be really painful to check, position at RFS may be challenging too. Runout has them all in one with relatively simple set-up and inspection equipment, so why not to take the advantage of it?

The fact that something has to rotate during runout check (either part or dial indicator) does not mean there has to be a rotational movement in reality. Imagine a static cylindrical sealing surface. In most cases it is a functional reuquirement to have it as round and straight as possible (apart from being smoooth), but can you imagine circularity inspection without rotating one of the elements of the setup?

Of course runout is not a cure for everything. It has some disadvantages - it cannot be modified by MMC, LMC, MMB and LMB, but still as a composite tolerance it is relatively user-, time- and money-friendly tool.

 

[Belanger]

On the grand scale, the only thing that "trumps" runout is profile. When teaching a class, I often ask students to name other GD&T symbols that are encompassed within total runout applied a cylindrical shape. (There are 7, well 8 if you count angularity which can be a generalized version of parallelism.)
But people often say that profile of a surface is controlled by total runout. Not quite, because a profile tolerance requires a basic dimension on the diameter of the cylinder, thus controlling size. Runout can never control size.
Just thought I'd throw this in

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

http://www.gdtseminars.com

 

[powerhound]

I don't think there's a question that runout is a powerful control but sometimes "with great power comes great responsibility" - Uncle Ben

I think the OP is a valid question. Clearly a runout spec on a non-rotating part is still legal, but you're depriving yourself of the potential use of an MMC modifier. I'm not saying a non-rotating part can always use one but position does seem to make more sense anyway.

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

 

[MechNorth]

I think pmarc and J-P described the situation well enough. Picture long pins (leader pins, guide pins, ejector pins, etc.); how else do you easily control them? As J-P noted, Profile (my personal favorite). Concentricity is a non-starter as it doesn't control what most people think it does; we aren't dealing with highschool concentricity here, but rather Y14.5

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[powerhound]

Sorry for interfering with an already well-stated situation.

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

 

[fsincox]

Tick,
When it comes to GD&T runout I think of it more as a "concept" than the method (as we all know ASME does not prescribe methods, see book). You just have to show it would pass if you could.

 

[CheckerHater]

as we all know ASME does not prescribe methods...

O yes it does, big time

 

[fsincox]

Wow, I meant it as a smiley when I wrote it.

 

[CheckerHater]

So I smiled and even laughed.

But I found “we all knows” in OP disturbing.
I still remember times when drawing was required to contain all the information necessary to manufacture and inspect the part.
When did it change to “drawing shall be prepared with complete and utter disregard to shop process”? When function became the only requirement?

(Don’t pay any attention to me; just an old man at the end of the week)

 

[ctopher]

It started changing when mfg went to China. ;-)

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion

 

[KENAT]

Well the principle of defining the end item goes back to at least 1994 and I suspect long before that.

Posting guidelines faq731-376

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

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

 

[johnchrc]

Checkhater,

More love today.... must be xmas spirit. I respect your opinion as mucch or more than anyone on this board. I'm not sayin your are alwaays correct becasue I only monitor this forum when I'm needing help or occasionally to provide input (I try to give back).

I started using GD&T in 2010 due to departmental move. I wasn't happy at first but quickly understood the necessity. Later...

Marry Xmas

- CJ

 

[CheckerHater]

Thank you CJ,
I am terribly wrong from time to time, but what’s the best way to support lively discussion?
Merry Christmas to you too