A quick question on total runout

[MacomMech]

My question is this:

If I specify a total runout of 0.05mm on an OD of 6.05 +/-0.05mm, does that mean when it gets inspected by QA the maximum allowable diameter is 6.15mm or 6.1?

 

[ringman]

6.1

 

[powerhound]

The size of the feature cannot exceed 6.1 but when the feature is at 6.1 it can run out .05 which gives it an actual mating envelope of 6.15.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[dingy2]

Total runout is always in RFS and is inspected on its actual size as long as the feature meets the size requirement. The maximum allowable size is 6.1 mm so 6.15 is nonconforming - it exceeds the size requirement.

Dave D.

http://www.qmsi.ca

 

[ringman]

Perfect form at MMC I suspect?

 

[powerhound]

Rule #1 would apply to the size of the feature but it would not apply to runout WRT whatever datum is specified.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MacomMech]

I'm having problems getting a tube manufactured without variations in a diameter making assembly more difficult than it should be, the diameter varied depending on where you measured the part, but still within the specified tolerance band. I'm hoping total runout will make things clearer for the manufacturer and for us to inspect.

Thanks for your answers, it comfirmed what I thought was the case.

 

[powerhound]

So to what datum(s) are you specifying total runout? You cannot just point to the tube and specify total runout alone. It must be referenced back to a datum or datums. If the tube is one diameter along the entire length then you must create datum target points or axes and measure WRT to the same ones every time. The other option is cylindricity but that one is very difficult to check.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MacomMech]

Oh sorry, information on a need to know basis.
I've specified a straightness tolerance on the tube axis of 0.2mm diameter. The tube axis is the datum and runout is relative to that datum.

 

[powerhound]

If you have a datum identifier attached to the centerline then that violates the ASME standard. You need to specify whether it's the axis of the OD or ID but you can't call the OD the datum and then specify a runout WRT the OD unless you have the datum points as I referred to earlier.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[fcsuper]

I agree with Powerhouse on this. It sounds like MaconMech is already applying it correctly, and that this is just a question of interpretation, which I think was well answered.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ewh]

I agree. The straightness tolerance should control it sufficiently, if the diameter tolerance is indeed appropriate. Adding runout will just confuse things, as well as making the part more expensive.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[ringman]

Macomech,
I believe that an axis is by definition straight.
I think what you are attempting to control is the 'derived axis' per the committee. NOt sure whether or not the proper method used.

 

[ringman]

Has straightness of an element been considered for the control? Just a thought.

 

[TheTick]

You need to rethink your original question. Runout is only a measurement of variation (indicator movement) through rotation and is independent of diameter.

Your part could have zero runout (perfectly straight centerline and circularity) but be too large or small diameter. Your part could have perfect nominal diameter everywhere but be bent so that it has excessive runout.

Honesty may be the best policy, but insanity is a better defense.

http://www.EsoxRepublic.com

-SolidWorks API VB programming help

 

[MacomMech]

Now correct me if I'm wrong, but putting a tolerance on the diameter fixes the limits of what is acceptable size wise, and the Total Runout is how much that dimension is allowed to vary over the length of that particular feature so long as the runout does not take it either side of the dimension's limits?

If I specify a dimension eg 10mm +/- 0.2 then when it comes to QA inpection any measurment between 9.8 and 10.2 is acceptable. However what I have been having are variations in the diameter depending where that feature is measured, could be 10.1 at one end and 9.9 at the other - still within spec.

It may be the manufacturer but the previous issue of the drawing had a GD&T paralell tolerance on that diameter and that didn't cure the problem, and we're talking over a length of 25mm.

Rant over.

Any other suggestions of alternatives to Total Runnout?

 

[Xplicator]

MacomMech,
First off in this case when dealing with a diameter, Total Runout controls simultaneously form (cylindricity), orientation and location of all surface elements of the diameter relative to the datum axis. It does not control size!

You say in a subsequent post that

"I'm having problems getting a tube manufactured without variations in a diameter making assembly more difficult than it should be, the diameter varied depending on where you measured the part, but still within the specified tolerance band."

So what you are describing as the issue during assembly is the actual local size measurement of the component. Perhaps the specified feature of size tolerance range is your problem here and it has nothing to do with form, orientation or location.

Please clarify so that we can best assist you.

 

[ewh]

If the diameters are within spec and the parts don't fit, perhaps the tolerance isn't what is functionally required(?)

"the drawing had a GD&T paralell tolerance on that diameter"
Parallel to what?

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[TheTick]

Now correct me if I'm wrong, but putting a tolerance on the diameter fixes the limits of what is acceptable size wise, and the Total Runout is how much that dimension is allowed to vary over the length of that particular feature so long as the runout does not take it either side of the dimension's limits?

Yes, you are mistaken. Runout is independent of actual diameter. Runout is a measurement of the "wobble" of a revolved surface.

Picture a bent or bowed rod of perfect uniform diameter.

 

[MacomMech]

Thanks for all the replies

The part is used in an assembly where a copper coil is wound around part of the 10mm diameter, so it doesn't have to fit into anything.

Variations in the diameter along the length of the feature cause problems getting the coil to operate within spec. The result is the coil winding company spends time re-measuring the part to confirm the best place to wind the coil.
The dimensional tolerance of the part is chosen to meet the requirements of the coil, it is the variations in diameter along the length of the feature that is causing problems.

If I was to use only a dimensional tolerance I would be looking at 10 +/- 0.025mm and that will be getting expensive