correct gdt symbol to use

[duk748]

hello - always a wealth of info here - i have a small eccentric shaft that was sent to our company from our overseas manufacturing facility - the drawing has the main shaft dia. as the a datum & the eccentric dia as being parallel to a & true position to a w/ a tolerance - this seems to be incorrect to me - i believe that the eccentric dia. should have a circularity datum to the main dia. and/or a parallel datum symbol - any thoughts on this - any info would be greatly appreciated - i cannot post a pic of the drawing do to not having access to the drawing at this time - thank you

 

[Belanger]

Circularity would have nothing to do the eccentricity; it only controls the shape (roundness). So position is the best one (parallelism's effect is already covered by position, so if the parallelism tolerance value is the same as position's, it would be redundant.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[duk748]

hello again & thank you for clearing this up - i had just never seen position used like this between 2 shaft dia.s - i understand now why parallel is not needed too - the part shows 2 datums one true position & the other parallelisum so i knew something was just not right - thank you again for your help -

 

[pmarc]

I am not sure if I am visualizing the application correctly, but if both shafts are nominally coaxial circular or total runout may be a way to go. These will not only control eccentricity of smaller shaft but also its form (circularity if circular runout applied or cylindricity if total runout used).

 

[MechNorth]

Pmarc, I think the intent is for the shafts to be eccentric, not coaxial.

The position callout works well. If the surface is anything other than cylindrical, then surface profile should be used.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com