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runout vs concentricity question

runout vs concentricity question

runout vs concentricity question

(OP)
If I mount the following object on a V block at point A and put a indicator at point B, what am I measuring? Basically I want to see if the two diameter's center lines are collinear.

RE: runout vs concentricity question

You are measuring circularity and coaxiality.

RE: runout vs concentricity question

(OP)
what if I trace up and down the smaller diameter? Is that runout?

RE: runout vs concentricity question

If you measure at one point at a time, it is Circular Runout. If you move the indicator longtitudinally while measuring, it is Total Runout. In total runout in this case, you measure circularity, coaxiality, straightness, taper, angularity.

RE: runout vs concentricity question

I cannot see your picture (tinypic.com is blocked in my place), but you are always better off placing your datum feature in chuck/collet when measuring either runout or concentricity.
If your feature A is not perfectly round, using V-block to establish axis of rotation is a major pain.
Just an opinion. smile

RE: runout vs concentricity question

There are situations where a V-block can give false compliance readings. Keep this in mind.

RE: runout vs concentricity question

If you leave the indicator in one position and rotate the part you are measuring circular runout. It is not possible to measure concentricity with a dial indicator. However, since runout will always be greater than concentricity it can be used as a quick check. If the runout is less than the concentricity requirement you are good.

Due note TheTick's statement about v-blocks. If your A feature has significant lobing it can effect the results.

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

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: runout vs concentricity question

tactical14,

Without touching the aspect of proper datum axis establishment by V-block at the moment, depending on how you will rotate and move the dial indicator or the part during the check, you may verify different things - circular runout, total runout or even ASME's concentricity. (dgallup, are you sure that it is not possible to measure concentricity [per ASME definition] with a dial indicator, of course assuming that datum axis is well established?)

What GD&T standard are you working to - ASME or ISO? Concentricity has different meaning in both, so it would be good to know what "Concentricity" means to you. Additionally, assuming you are in ASME world, "I want to see if the two diameter's center lines are collinear" makes me think that you are very close to mix Concentricity with Coaxiality.

RE: runout vs concentricity question

Concentricity vs. runout is a perennial debate in GD&T. The requirements for establishing concentricity are far greater than for runout.

Concentricity simply can NOT be fully verified with a chuck or V-block. It requires more. That is one reason that runout even exists as a spec. Runout is simpler to measure and in most cases is sufficient.

Many people specify concentricity when they really mean runout, and even specify measurement methods for runout. It is "folk GD&T", and not correct.

RE: runout vs concentricity question

TheTick,
Let's say that I have a will, time and money to try to inspect ASME's Concentricity of an external cylinder relative to datum axis derived from other external cylinder with the use of single dial indicator and a chuck. I place datum feature cylinder in the chuck - the axis of the chuck becomes my datum axis. Then I start to probe toleranced cylinder surface with the dial indicator, but not in a continuous way, like I would do in case of circular or total runout check. Instead of it, I probe one point, register the indicator reading, and then rotate the part by 180 degress around datum axis and register second reading. Next I analyze magnitude of difference in readings and divide it by 2. This is the distance of single median point from datum axis.

By doing this I inspected and analyzed one pair of diametrically opposed points. And I can/have to do it for other points in the same cross section and in other cross sections along the axis of toleranced cylinder.

Wouldn't it work as a check of actual Concentricity error?

RE: runout vs concentricity question

No, mostly because it does not account for form variances. No guarantees on the roundness or cylindricity of the surfaces, thus no guarantees on v-block readings for concentricity.

RE: runout vs concentricity question

I mentioned nothing about v-block usage in my example - I want to use a chuck. In my firts comment I also stated that I did not want to touch the aspect of datum axis establishment by v-block.

In the light of that, do you still think that my method of inspection does not lead to proper actual Concentricity error check?

RE: runout vs concentricity question


Pmarc,
Is the technique you describe any different from using a chuck and 2 indicators?
As concentricity is described as condition of two opposite points, chuck and 2 indicators should be perfectly fine IMHO.

The Tick,
As concentricity controls TWO OPPOSITE POINTS, and runout controls ALL THE POINTS, runout is more restrictive control than concentricity.
If part passes runout requirement, it automatically passes concentricity reqirement of the same amount, and THAT IS the reason that runout even exists as a spec.

RE: runout vs concentricity question

CH,
No, geometrical fundamentals behind my idea is no different than in case of use of 2 dial indicators. The only difference - you will need two of them, I will need just one.

RE: runout vs concentricity question

Imagine surface A is an ellipse and surface B is a corkscrew.

RE: runout vs concentricity question

The Tick,

Quote (pmarc)

Let's say that I have a will, time and money to try to inspect ASME's Concentricity of an external cylinder relative to datum axis derived from other external cylinder with the use of single dial indicator and a chuck...

There is no need for envisioning some fancy scenarios with ellipses, corkscrews and v-blocks. I was asking for simple answer to the simplest possible case of all.

RE: runout vs concentricity question

Response noted, pmarc. Wasn't talking to you.

RE: runout vs concentricity question

Does corkscrew have opposite points?

RE: runout vs concentricity question

Trying to help tactical14 understand why a V-block is not a good idea. Remember him? He's the guy we're trying to help.

RE: runout vs concentricity question

So am I.
If corkscrew doesn’t have opposite points, then concentricity doesn’t apply.
Does OP part look anything like a corkscrew? Because if it’s not, you are not helping.
(I won’t post anything else here, I promise)

RE: runout vs concentricity question

Sorry. I asked you to use imagination. That might have been a stretch. An actual corkscrew would be extreme, but a very subtle one is quite possible (and even common in some applications).

Another example:
Posted here is an example of opposing ellipses which would show zero runout when measured on a V-block. Again, this example is exaggerated for effect.

It is also possible to have shapes that appear to have uniform diameter when measured with calipers at different orientations but are not round.


RE: runout vs concentricity question

TheTick,
It would be good if your attachments vere in formats readable to all of us here. I do not have Solid Works, so can just imagine what your "another example" is about.

You seem to stick to V-block issue. The thing with it is that if you are sure that datum feature experiences significant form and/or size errors (within stated limits of size if we are in ASME world), because you previously checked it, v-block should not be used for datum axis simulation, exactly due to the reasons you mentioned. In reality it happens quite often that datum features are of sufficient form and size quality to enable v-block usage. Sometimes v-block(s) is(are) the only reasonable choice.

I have a feeling that v-block was not the clue of OP's question. Of course it is very good that the caution was urged by you and others, but did it bring him any closer to understand what can be measured by dial indicator on feature B? I do not think so.

RE: runout vs concentricity question

I seem to have read the original question and not gone off into the weeds.

I've been over the concentricity vs. runout thing many times in my career. There are thems that gets it and thems that refuses to. Not much in between.

Sorry about the format. I tried to post images but it didn't take. Posting composite image of the model.

batHonesty may be the best policy, but insanity is a better defense.bat
http://www.EsoxRepublic.com-SolidWorks API VB programming help

RE: runout vs concentricity question

Technically, it does not have to be true that for these ellipses zero runout error will be inspected.
If the part stands still and the indicator rotates around datum axis, the error will be there, don't you think?

RE: runout vs concentricity question

The part will show HUGE runout but zero concentricity smile
(Sorry, I know I promised to keep quiet)

RE: runout vs concentricity question

Part was designed to demonstrate ZERO runout when checked in 90° V-block. This is why V-blocks are bad, m'kay?

Are you going to rotate the indicator around the axis? How are you going to set that up without a mandrel? If you had a mandrel, why are you using a V-block?

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