Circular/Total Runout

[EngJW]

Well, I did search here and on the internet and I think I understand what these terms mean, but I wonder if anyone can give examples of where to use one or the other.

If you have a diameter that is going to be used for something like a needle bearing race I can see using total runout. However, if all you want to do is press a ring or hub or something onto it, it seems that circular runout would be enough. If not, then maybe we should be using total runout everywhere and never bother with circular. I suspect, however, that total runout is over-used, at least where I am.

What do you think?

 

[ctopher]

I normally use TR on circular parts that spin or turn in some way. If the part is stationary, never turns, I use runout.
But ... this not always the case. Depends on the design.

Chris
SolidWorks 07 2.2/PDMWorks 07
AutoCAD 06
ctopher's home (updated 02-10-07)

 

[dingy2]

Both circular and total runout are used on SMALL cylindrical parts and are checked in a divider head or chuck with an indicator and stand.

Circular runout combines two characteristics on the cylindrical feature relative to the centre line developed with the datum diameter. It confirms roundness of the feature and also concentricity. It does not control the shape of the feature. In other words, is the cyclindrical shape of the feature tapered? If one measured it in the centre or at the ends, are they the same diameter. Circular runout does not confirm this.

Total runout is like circular runout BUT it also confirms the shape of the feature. We now control roundness, concentricity and also shape of the feature. When we confirm total runout, the readings we achieve on the dial indicator could be all roundness, all concentricity or all shape but usually is a bit of everything.

Total runout is very stringent and costs $$ to meet the requirements. I would suggest using it sparingly and a Designer must have rational on its use over circular runout.

Go to any tool room and ask them to check the runout. They will always perform a circular runout.

Just a suggestion - If you have 2 cylincrical male features that can be checked for runout (either one) and must fit in some sort of assembly, I would suggest replacing either runout with positional tolerances at MMC.

Dave D.

http://www.qmsi.ca

 

[EngJW]

Sounds like total runout is a composite then. I agree, most shop people I know would just check circular runout. Also, if you had a pilot diameter only .19" long, it would probably be difficult to check total.

If you had a bearing journal and you specify total runout, is it incorrect to also specify roundness and taper?

For example, if you had a crankshaft I think you could only use taper, roundness, and possibly position for the crankpins, but for the main journals you could use total runout by itself.

 

[dingy2]

One would only use circular or total runout on a completely round feature.

On a bearing journal(mains), I would suggest total runout but your shop better figure out how to check it.

If one specified total runout on a journal, the Designer can specify roundness as a component of total runout. The value MUST be smaller than the total runout.

If one wanted roundness and taper as a component of total runout, I would suggest using cylindricity. Again, it is a component of total runout and the value must be smaller.

If we are talking about a rod bearings on a crankshaft, I would suggest positional tolerances in RFS to show the position of the bearing using polar tolerances. Make sure that the true position (theoretical) is shown on the drawing in basic dimensions.

Each bearing would be reflected with cylindricity. We can tighten up roundness as a portion of cylindricity but the value must be smaller than cylindricity.

Wow, heavy duty question for sure.

Dave D.

http://www.qmsi.ca