Runout includes profile?

[Belanger]

This is a two-pronged question for all of you regarding total runout...

First, I claim that total runout may be applied to a cone, IF the angle of the cone from the datum axis is given as a basic angle.

A colleague insists that it can't; his main evidence is that Y14.5 doesn't give an example of one (flimsy, eh?). But I point to paragraph 9.4.2.1 (of 2009 std), which glaringly omits "cylindricity" from the list of other characteristics covered by total runout. Thoughts?

Second, that same paragraph mentions "profile of a surface" as one characteristic that total runout may control. We know that profile of a surface must be applied to a true profile (meaning a basic diameter), but I maintain that runout tolerancing is not meant to control size -- the diameter of the part should not be basic. Though the standard doesn't say this latter item, I infer it because they make no mention of the dial indicator being zeroed at a specific distance from the datum. Thoughts?

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

 

[dingy2]

J-P:

Either runout does not control size but circular runout controls a combination of roundness and coaxial while total runout controlling, in addition to circular runout, "straightness, angularity, taper and profile of a surface" per 6.7.1.2.2 in the 94 edition.

Yes, if the feature was tapered, the taper must be reflected in a basic dimension.

Dave D.

http://www.qmsi.ca

 

[TheTick]

Good luck measuring total runout on a taper. I'd like to know how that goes.

 

[Belanger]

I don't see why it's any more difficult than checking total runout on a straight cylinder.

For a regular cylinder the dial indicator has to be rigged so that it travels parallel (0º) to the datum axis.

So for a taper, the dial indicator is rigged so that it travels at a prescribed angle (say 10º). Either way, the angle of travel must be calibrated first!

But yes, both of these are more difficult than checking circular runout.

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

 

[Belanger]

Right Dave, but do you read that as saying that total runout controls size? (Since it mentions profile in the explanation.)


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

 

[TheTick]

Total runout measures the total deflection over the entire length of a revolved surface. A tapered surface will eat up a lot of that deflection just by the taper. Effectively total runout contains a surface within a cylinder of a given thickness.

There is nothing in the definition of total runout that makes adjustment for the indicator deflection changing due to surface taper.

 

[Belanger]

But Tick -- I'm saying that "what if" the taper is given as a basic dimension?

If you say that it's not possible since the standard says nothing about a basic dimension, then I think paragraph 9.4.2.1 of 2009 should say that it controls cylindricity also. (It does say "taper" but I can control the taper even on a cone.)

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

 

[dingy2]

J-P:

TheTick is correct when it comes to confirming total runout on a taper. Circular runout on a taper is easy using a divider head or chuck but total runout?? The only way is to use a machine chuck setting the tapered angle but that is not a measuring instrument. I know that there must be equipment out there that can do it but it would have to be a special purchase.

Figure 6-48 example explains the meaning of total runout and it is not about a true profile. It states "The feature must be within the specified limits of size.".

Dave D.

http://www.qmsi.ca

 

[Belanger]

Thanks Dave.
I was right in thinking that runout does NOT encompass profile of a surface. ASME needs to revise paragraph 9.4.2.1.

But regarding inspection of total runout: we all agree that circular runout is easy (relatively). But are you saying that total runout even on a straight cylinder is difficult?

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

 

[mfgenggear]

depending on the geometry,a taper can be checked for total runout. if it's a shaft it can be located between centers on top of a sin bar, tilted to the correct angle.
then the entire surface of the taper can be verified.

an other way would be to have a 4 th axis index head & that can turn & tilt to the correct angle.

 

[Belanger]

That's exactly what I was thinking.

If total runout has the indicator move along a rail parallel to the axis, what's the big deal about tilting the rail (or the part) to a prescribed angle? The real question is whether the standard even allows a basic angle to be mentioned.

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

 

[axym]

John-Paul,

Here's my take on it.

First, I would say that total runout can be applied to a cone. Or a sphere, or any surface of revolution. It would just be very difficult to inspect these shapes using a dial indicator method, because the indicator would have to be tracked normal to the feature's basic profile. This requirement applies to circular runout as well, although it is often overlooked or ignored.

Second, the statement in Y14.5 that total runout can control profile of a surface is incorrect and should be removed. A runout tolerance does not control the size of the feature.

There is another example in Y14.5 that muddies the waters even more. See Figure 6-24 in '94 or Figure 8-18 in '09. Before I begin my rant, what do you guys think of it?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Belanger]

Hmmm Evan,

I see what you're getting at. That profile of a surface is not applied to a "true profile" because of the +/- dim on the diameter.

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

 

[axym]

John-Paul,

Yes, the diameter is plus/minus and not basic. So the profile tolerance's usual control of the "magnitude" of the feature is overridden in this case. Of all the things in Y14.5 that drive me nuts, this might be number one. The profile tolerance ends up controlling the form, orientation, and location of the cone - everything but the size. This is exactly what a total runout tolerance would do. So why did they avoid using total runout on the cone, and choose to use a mutated profile instead? To me this doesn't make sense, and is an example of Y14.5 being example-based and not rule-based.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[fsincox]

John,
I think it can too, The reference you stated says circularity and taper, I believe that is cylindricity, just like they say coaxiality not position or concentricity. They slipped in some generic terms. I asked this in another thread, isn't runout just an inspection method not really a functional requirement?

 

[mfgenggear]

I have seen where a profile geometric tolerancing is specified, to control diameter, angle & so on.
in addition runout or total runout is also applied.
where that feature needs to more precise.

but it appears to me total runout is specified normally to parts that simply rotate & are not static.

 

[mfgenggear]

run out & total runout (when perpendicularityis required) are very easy to verify on rotating shafts, gear shafts, & so on.

 

[fsincox]

This is why they love it so, it is easy, some here are worried we apply tolerances that are too complicated for the down stream, I say this is the opposite case, it is easy for them but what does it mean to me, nothing. How much taper? How much eccentricity? How much roundness? This is what I need. When it doesn't pass then we have to sort it out.

 

[mfgenggear]

The importance & cost of the product will dictate the quality required. GD&T is that tool to make sure the designers requirements are satisfied.

GD&T is not that difficult, once one is trained for it.
and if applied correctly it can improve you drawing.

back to the original post
runout is a seperate feature it should not be used to
control size of diameters.
It is one of the more easier attributes to check
& so is roundness, taper,cylindricity & true position.
I have done it all.

The one I dislike is profile of any surface. however
it can be easily checked with the right equipment.
if the manufacture doesn't have the right tools.
thats an other story.

 

[fsincox]

"Runout doesn't control size". If the relative tolerance numbers are small to the size tolerance that is not really true. So to ignore it beacause it was not stated there is silly, they make general statements, these standards are not tablets from GOD.