【转帖】what is the difference between runout and concentricity

yang686526

what is the difference between runout and concentricity???
1. what is difference between runout and concentricity, esp. just want to get a coaxiality.
2. does runout applied on rotating part only? if not, then i thought it is same as concentricity. am i right?
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one more question about the concetricity vs runout.
can i use cmm to measure the concetricity and runout? and does cmm can get the exact measurement?
they are just about the same. total runout is for a rotating part. i don't use concentricity because i believe it is more difficult to inspect than runout.
chris
solidworks 07 4.0/pdmworks 07
autocad 06
runout measures the variation at the surface level of the part.
concentricity is used to identify the axis of the part.
in general, concentricity is most often used in highspeed rotating parts where balance is desired, such as crankshafts and camshafts to name a couple.
runout is measured by rotating a part, but it is not necessary that the part be rotating in its application.
concentricity is much more difficult to measure and verify.  concentricity requires verification of size, circularity (roundness) and position of features.
often i have seen concentricity called when runout is actually what is measured. this can be a problem for iso or qs documentation.
unless you are dealing with extreme precision and speed, runout is almost always a sufficuent measure of whether features are coaxial.
i don't know if we beat this question to death at one time but here it goes again.
runout (both circular and total) is a surface condition on a cylindrical feature relative to a centre line created through another cylindrical feature sharing the same centre.
circular runout combines roundness and off centre while total runout has the addition of shape of the feature along its length.
both are performed on small cylindrical products (such as screw machine products) that one can set up in a chuck or divider head and is perform using a height gauge (stand) and dial (digital) indicator.
concentricity is the median points of diametrically opposing sides of a cylindrical feature relative to a centre line created through another cylindrical feature sharing the same centre.
this is tough stuff to measure and most people who think they are checking concentricity are really checking the position of a feature in rfs. keep away for concentricity.
it is usually measured using a cmm and is always in rfs.
dave d.
very well stated dave d. a star for you.
bradley
solidworks premim 2007 x64 sp4.0
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the others have explained what you ask.
my 2c worth, from my experience once you think it through concentricity is rarely the correct tolerance.
more often one of the runouts or position is more appropriate.
the above is a sweeping generalization but hopefully gives you some food for thought.
kenat, probably the least qualified checker you'll ever meet...