correct datum or feature symbol

[duk748]

hello - i have a shaft that has one diameter & another diameter eccentric to .08" - which is the correct datum symbol to use to have a relationship from the 1st diameter to the other?? - can i use true position?? - any help would be ver appreciated - thank you

 

[ewh]

Depends; true position, runout and concentricity may all be valid callouts. How will this part be inspected?

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[duk748]

hello again & thank you for the reply - i am really not sure at this point how the inspection will be - a reference drawing that was used has the eccentric dia. held parallel to the main shaft datum "a" - this does not seem right - the eccentric axis is dimensioned to a close tolerance to the main axis & the cylindricity datum has been used on the eccentric- this also does not seem right -
any ideas????

 

[TheTick]

Are the Ø's concentric with allowable deviation of .08"?

Or are they .08" apart by definition/dimension?

 

[duk748]

they are .08" apart by definition/dimension - this axle is for a roller assembly to be able to adjust the roller to the rail it travels on hence the eccentric

 

[ewh]

Ah... I think you should use positional in that case.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[ringman]

If you were to dimension the dias with a .08 dimension,bsc, between the centers and give a positional tol to one with respect to the other, that should work.

 

[duk748]

hello again & thank you for all the help - i thought true position was the correct way to go but i also knew this was the place to find the correct answer - just one last stupid question - what does "bsc" mean in the last post ??
"use basic dimension??"

once again i thank everyone

 

[ewh]

Yes, a basic dimension. Way back when, "BSC" was used instead of the box.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[KENAT]

ewh & ringman have you covered.

Rememember the effect that size variation in the two shafts as well as their locations with respect to each other will have given your application.

Sure they're nominally .08 but what are the upper and lower limits to this and how is the tolerance budget best distributed for your application.

KENAT, probably the least qualified checker you'll ever meet...