Controlling Positional Tolerance of a Slot Axis

[jmarkus]

I have a slot (elongated hole) on my part which I wish to give a positional tolerance. The size tolerance for the slot is given, but I wish to control the centre of the slot within a diamteral zone. Can I use the diameter symbol in the FCF? I am getting conflicting answers within my organization, so I thought I'd throw it out there.

Thanks,
Jeff

 

[ewh]

No. Since this is a non-circular element, you need to control the center planes, as opposed to the axis.

 

[ctopher]

maybe check out thread1103-115899

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP1.1 / PDMWorks 05
ctopher's home site

 

[jmarkus]

Umm...Thread1103-115899 is the one I started on a different topic (using the slot as a datum). What I am asking now is can I control the axis of the slot in a diametral tolerance zone. The alternative is a square tolerance zone - which, from what I understand, was one of the reasons GD&T improved over simple dimension tolerancing.

Jeff

 

[ewh]

Slots are best controlled with two FCBs, one for the vertical axis and one for the horizontal. Granted, you do end up with a rectangular tolerance zone, but you have more control over it than you would with the square tolerance zone that +/- dimensioning would give you.

 

[ctopher]

oops, sorry. I did a search, didn't realize it was yours.
Anyway, I agree with ewh.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP1.1 / PDMWorks 05
ctopher's home site

 

[jmarkus]

Okay, I think I understand. Now when would a "BOUNDARY" callout be appropriate?

Jeff

 

[drawoh]

jmarkus,

The GD&T positional tolerance is not just for round things and holes. Check out page 92 in ASME Y154.5M-1994, where they apply it to a pitch circle of rectangular slots.

I have only one objection. The whole point of a slot is that you only need to be accurate in one direction. The positional tolerance controls two.

JHG

 

[looslib]

In the Y14.5 training I had, we did a slot with the width controlled by True Position of .001 and the length controlled by True Position of .020.


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