Using Runout to Measure Concentricity

[@nandhu150390]

Useful mate👌

[@PT-qv6bu]

Best explanation I have found! thank you very much!

[@kslats916]

Please explain more about how 'Datum A is Fixed axially + rotated' as shown in the lower left view. I suppose in practice there are multiple ways this may occur like that end is still in the lathe and freshly machined. What if it's been removed from the lathe and the part has been passed over to metrology? They would likely place Datum A in a Vee Block and rotate but datum A has the .05 tolerance and may not be circular.

[@Gdandtbasics]

Without doubt, our desire would be to inspect this while the part was still in the lathe. This is because our reference was for the machinist to use Runout as the method of measurement. Though not our desired method (and less accurate), I think that many of us have been forced to use a set of vee blocks to inspect Runout. If this must be done, I have always used the strap clamps that come with the match set vee blocks as a method of keeping the part from “bouncing” due to Circularity error. However, I will not drive the metal clamp straight down onto my part. I will place something in between that will allow me to apply very slight pressure while still being able to rotate the part. Again, this is not desired, but desperate times call for desperate measures! Hope this helps!

[@vishnunair6675]

So both concentricity and run out can be checked using the same setup (dial gauge and collet). If during measurement of runout, the derived median point is ascertained from diametrically opposite points, then we can measure concentricity too.

[@Gdandtbasics]

Checking concentricity is similar to checking runout except it involves a bit more math and an understanding of how far away your indicator is from the axis of the rotation when you collect your diametrically opposed elements so you can then calculate how far away the derived median point is from the datum axis. Like we mentioned though this requires measurements to be taken exactly 180 degrees from each other so that we can calculate where that derived median point is with respect to the datum axis. This is alot more work than simply reporting the total indicator reading during a full rotation, as you would when checking runout.

[@sem7207]

Circular runout is more stringent control than concentricity, because it also rejects form error such as the oval feature that was shown. That oval shaped feature could have near perfect concentricity with all midpoints accurately centered to the datum axis. So if runout is checked instead of concentricity, no non-conforming features would pass. Total runout check does not have an advantage over circular runout check as an alternative to concentricity inspection, because concentricity, despite of the continuous cylindrical tolerance zone, doesn't limit taper, barreling, waisting, or waviness in the axial direction.

[@tcteoh57]

Base on the lower right diagram, if got to define concentricity in diameter zone, it should multiply by 2 from the indicator reading?

[@Gdandtbasics]

For runout and total runout, the total indicator runout is the reported value and it must be less than the listed value in the feature control frame to pass. For concentricity, it is not simply enough to multiply the indicator reading by 2. You must take 2 opposing measurements 180 degrees from each other to find the exact midpoint between these two measurements. Then that midpoint must remain with in a cylindrical tolerance zone that is centered at the datum axis. This is very hard to inspect without the right equipment. For this reason we recommend utilizing position or runout to control coaxial features instead.

[@crazyingenieur3277]

Total Runout = Concentricity + Cylindricity If you measure total runout and it is within 0.030, then concentricity is within 0.030 as well. When you refer to Y14.5, you must always provide the version! In 2018 version, they removed concentricity and symmetry.

[@孙小圣-d8u]

Can Total runout be used instead of coaxiality? For the same geometric tolerance value, which one is more stringent than Total runout or coaxiality?

[@Gdandtbasics]

By Coaxiality im assuming you meant Concentricity? If so, i would recommend using total runout instead, as its much easier to inspect and generally is more applicable to the functional intent of the part. The value however is not directly translatable as they are very different tolerance zone shapes. As far as which one is more stringent, it depends on the tolerance value chosen for each symbol.

[@CAMER_21]

can you do it practically ???

[@chrisb8776]

hi i would like to ask you how is it possible to measure runout on a surface that is perpendicular to the datum or is this a possible engineering mistake?

[@Gdandtbasics]

Definitely no mistake. Total Runout is the "preferred" control as it is a 3D control. The Runout controls require a Datum Axis and it is simply interpreted as "Perpendicularity". Place a dial indicator parallel to the Datum Axis and on the face/surface to be inspected. Move the indicator towards the axis (center) and then to the O.D. and this is Total Runout on a surface perpendicular to the Datum Axis. Hope this helps! Thanks

[@virenderthakur1611]

Can i coll