axis datum - bearing

[cervantes]

Hi,

just a simple question I think,

fig 9.7 from ASME is more or less the only suitable example for this

generally it was hard for me to find any examples for runout with more than one datum (except fi 9.7) so I just to ask if this is correctly described:


I am measuring runout , but for meaurement process, the pin (yellow) goes thru a bearing, which may tilt a little bit which can deflect the measurement - and I want to reduce that effect

in application, surface B is connected to another surface so this effect is decreased

so in the fact - I shall also specify a datum B (which means that tool for measurement shall change its shape), which means that firstly - I am pushing pin thru bearing till it stops on surface N

am I right?

 

[Tmoose]

I'd make the bore for the bearing OD a datum for other features that influence bearing alignment to other stuff.

http://medias.ina.com/medias/infoimg/bilder/imageref_90411787_All.gif

 

[mkcski]

Generally, Datums (motion constraint) should be assigned based on function and not inspection. I think I agree with Tmoose, but can you give us more of how the part works?

 

[3DDave]

I would use the bearing bore and make sure that it's runout/orientation are not larger than the installation will accept.

The bearings will be very closely built per their spec so there is no need to bury that contribution in a case where angular misalignment capacity of the bearing can exceed (which it should) the requirements of the installation.

Plus it means finding out early in the process, possibly while still on the mill.

 

[cervantes]

didn't have too much time lately but I read all your opinions

we are already proceeding with solution which is similar to 3DDave proposal

thanks

 

[powerhound]

As a side note to an already solved problem: you can't add a planar secondary datum reference to an axis as primary and expect a different result. The only way a plane is used in the construction of a datum axis is when it is primary with an axis as secondary.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[3DDave]

tmoose - that example image is scary. I'm sure there is some significance to applying two datum symbols to the a single feature. I don't see what is gained by making a feature parallel to itself, though maybe the parallelism callouts are intended to apply to surface elements only in an attempt to augment the circularity callouts to create cylindricity, which would be the expected callout.

 

[Tmoose]

Hi 3DDave,

GD&T is not my first language by a long shot.

The image I linked was INA/FAG.
I believe the A and B are separate datums for the diameters, which have their own tolerances that I guess they want to exist separately and not be mucked up by the coaxiality/total runout, perpendicularity etc.

SKF is similar but different.

http://www.skf.com/pages/jsp/catalogue-table.jsp?id=tcm:30-6533