【转帖】runout relative to same features axis

yang686526

runout relative to same feature's axis
hi,
i am working on a legacy drawing that i am reviewing for gd&t correctness. this part is a shaft that is calling for circular runout on the od surface referenced to shaft dia as reference datum(please see the attachment). i know better ways of controlling this shaft but i can only change it if it is against y14.5. i can't question the design intention because they were making these parts before???
is there anywhere in y14.5 that prohibits using axis of same cylinder as ref for run out control of its face?

that drawing is wrong according to asme y14.5m-94. one cannot have circular runout relative to its own diameter. it must be relative to another diameter that shares the same axis.
i would suggest changing that to roundness but make sure the roundness tolerance is inside the size tolerance range. it the size tolerance is +/- .010, then the roundness must be no more than .020 and probably, much less.
if this is the complete drawing, then one does not need a datum on the od.
dave d.
hi dave,
i agree with you regarding the callout. i just can't find the item in asme that backs it up.
i am dealing with a tough checker and definition of runout is not clear on this issue.
thank you,
kaveh  
para 6.7.1.3.1
"where features to be controlled are diameters related to a datum axis, one or two of the diameters are specified as datums to establish the datum axis, and each related surface is assigned a runout tolerance with respect to this datum axis."
i have only seen runout of a datum surface controlled relative to itself in the case of two datums establishing a datum axis collectively, but the above quoted paragraph seems to allow a surface runout relative to the surfaces axis.
when the people fear their government, there is tyranny; when the government fears the people, there is liberty.fff"> - thomas jefferson

use datum targets to establish an area to be used for fixturing (i.e. a portion near the end).  then the rest of the surface is kosher for runout spec w.r.t. datum.
what if you were to use a combination of roundness and straightness of an element?  would that not serve the same intent?
roundness is similar to circular runout except circular runout one sets up on another diameter that shares the same axis. in both cases, the part is rotated with a dial indicator sweeping the circumference. one can confirm either requirement in any location along the feature and report the worst condition.
roundness and straightness could be combined in a cylindricity call out and it would be comparable to total runout if we had 2 diameter on the same axis.
dave d.
in fig. 6-52 page 194 the datum d is referenced by itself in the 0.05 runout callout (see the attachment) is it similar to my case?
wow, this is a can of worms.  i never realized it before, but y14.5m-1994 seems to indicate that runout control of a feature relative to its own axis is legal.  6.7.1.1.1 on page 189 says:
"each considered feature must be within its runout tolerance when the part is rotated about the datum axis.  this may also include the datum features as a part of the runout tolerance control where so designated."
the diagram pointed out by kmansoor supports this.  the circular runout tolerance on the datum d feature references datum d.
i can't say that i understand why this is allowable or why anyone would use this technique.
i agree with thetick that if datum targets near the ends of the feature were specified, then the runout of the remainder could be checked.  if datum targets were not specified, however, it doesn't make sense to me.
evan janeshewski
axymetrix quality engineering inc.
kmansoor,
it might be legal to specify but as you said parts are being produced from quite some time how is quality inspection been done with this kind of condition.