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runout used on rotating parts only?
3

runout used on rotating parts only?

runout used on rotating parts only?

(OP)
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?

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

(OP)
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?

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

Quote (bxbzq)

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
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RE: runout used on rotating parts only?


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_Newsl...

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

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.

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

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 www.profileservices.ca
TecEase, Inc. www.tec-ease.com

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

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.

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?


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)

RE: runout used on rotating parts only?

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 xmastree

- CJ

RE: runout used on rotating parts only?

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

RE: runout used on rotating parts only?

To the OP, my vote is NO!

RE: runout used on rotating parts only?

Frank,
Could you be more specific? I am curious what arguments hide behind this short but absolute statement. Thank you.

RE: runout used on rotating parts only?

OP: “…I think it's legal, but is it really good practice?”
Fsincox: “…my vote is NO!”
Am I right?

RE: runout used on rotating parts only?

IMHO: CH's statement of 15 Nov 12 pretty much sums it up. Book it.

ted kralovic

VisVSA, NX-6, Macbook, iPhone 3GS, Garmin 765T, Garmin Forerunner 405, Garmin eTrex Vista Hcx, among others

RE: runout used on rotating parts only?

CH,
Right, I gave my reasoning before, so I was just trying to keep it on track and simple, I would love to see all of your positions on the OP, too.
pmarc,
It sounds like we basically agree,

RE: runout used on rotating parts only?

I'm still puzzled as to who "we" are in the OP.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: runout used on rotating parts only?

I feel sorry for the state of the industry where someone is questioning legality of using run-out on round part.
sad
Is that a position, Frank?

RE: runout used on rotating parts only?

CH,
I didn't realize there was a question on using runout on round parts, it is the not easy to actually rotate parts I was thinking "we" were concerned about. Spindle housing bearing bores is my common example. The bearing manufactures often specify runout tolerances for mating components so I use them even if the part is not easily rotated.

RE: runout used on rotating parts only?

(OP)
What about a rectangular block with coaxial holes one of which being datum feature and rest of holes are controlled relative to the datum axis with runout tolerances? In this case you can rotate the dial indicator to check the holes. Good practice?

RE: runout used on rotating parts only?

Bxbzq,
In your earlier post you appeared like you objected to using runout on the piston.
No, I would normally not specify runout to check counterbore. If you read my post carefully and followed the link, you would see what kind of part will commonly benefit from using layout.
The good rule of thumb will be: if the part rotates during manufacturing (not necessarily during “function”), it may benefit from using runout during inspection. Nevertheless, one can actually devise a fixture to check “not easy to actually rotate parts” as well. Look at this picture:
http://www.sweethaven02.com/Automotive01/fig0360.g...
There is no need to spin engine head.
(It says “concentricity”, but we all know it isn’t smile)
In thread about partially-opposed FOS I stated that “Every single dimension, tolerance, or geometrical specification can be applied in the way that’s legal, but useless. Every rule can be misused and abused.”
I stand behind this statement. Nobody is holding gun to your head. You are the one to decide what the best tool for the job is.

RE: runout used on rotating parts only?

I would not use runout on a "real" counterbore because it is not a functional requirement, it is a MMC requirement.

RE: runout used on rotating parts only?

Here is the thing: if your counterbore passes, say, 0.10 runout requirement, it automatically passes 0.10 position requirement, either MMC or RFS (not like I would endorse it as "good practice")

RE: runout used on rotating parts only?

But that's overkill, unless you are also worried about the circularity of the counterbore.
So I don't think we should focus too much on how the part is made, nor on how it's inspected. Stick to function!

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: runout used on rotating parts only?

CH,
I understand some in the shop may want to check it that way on a coaxial situation, that is fine by me, as long as they only use it to confirm that it meets the position requirement I placed on it. I would not use runout as the callout for it though.

RE: runout used on rotating parts only?

I agree.
This is why I cannot see why there is so much drama.
If it is your design, you apply requirement that you believe is the best.
If you are manufacturer, and you receive the drawing with runout applied to “counterbore” you have 2 choices:
You device jig similar to the one on the picture and charge customer for it.
In bad case where reliable fixturing is not possible, there still way out. Even though Y14.5 provides no number or formula, it actually has requirement for datum feature to be “sufficient” (sorry, cannot quote exact paragraph right now), so you may claim (rightfully so) that control is not standard compliant.

RE: runout used on rotating parts only?

Off-topic clarification:
"We also say a well drafted drawing tells how the part works."
I am not among this "we", as I was taught that the purpose of a detail drawing was to completely define a part, not how it works or is to be used, or even how to make it (except in specific cases).

"We say inspecting a part is a process of simulating part's function or assembly."
This is not entirely true, especially if there are simpler methods which can be used to ensure that the part meets its definition.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: runout used on rotating parts only?

(OP)
Should I say complete definition is first level of drafting? A complete drawing could have inappropriate specifications.

RE: runout used on rotating parts only?

If the drawing contains inappropriate specifications, would it be considered complete?

All levels of drawings should completely define the part/assy that they are addressing. Component parts should have already been completely defined, unless further operations are required at the assy level.
The purpose of an engineering drawing is not to tell how the part/assy works, just to fully define the item (so that it will work as designed). How the part/assy works is better accomplished thru separate documentation, such as manuals or instructions.
Of course, different industries tend to follow different practices, but in the more strict sectors such as aerospace, my above comments are accurate. In other sectors, where perhaps manufacturing tends to drive engineering, your position may be valid.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

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