I am looking to simplify drawing for a sheet metal component. It's a custom handle used on a standard ball valve so the tolerances can be pretty loose. The complex shape makes it difficult to clearly and completely dimension. I know that the vendor is going to use the model to laser cut the flat shape. Our quality team is going check the important dimensions and for the rest, they will hold it up to a clear overlay. Considering all this, I am looking to call out the important dimensions and then create a global tolerance that ensures that the general shape matches the model. I was thinking of placing a global profile tolerance in the notes that cover all undimensioned surfaces. Can I do this? If there a better way? Drawing is attached.
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GD&T Question - Properly Defining a Global Tolerance
- Thread starter efulm4444
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The primary datum feature should have the most influence on the installed orientation of the part. The small fragement surfaces that make up datum feature A don't do that.
Secondly, the item that is functional is the width of the slot. The valve can be operated with channel locks. The tab is serving to stop people from going too far and closing the valve.
Mainly I would indicate a small area as a datum target area where the handle fits flat on the valve as the primary datum feature, with a flatness applied to that area, the narrow width of the slot as the secondary at MMC, with a perpendcularity to the primary datum feature and the length of the slot as the tertiary feature at MMC, also with a perpendicularity to primary datum feature.
The sides of the tab need to have a better control than all the rest, maybe a position tolerance on the width of the tab. Profile on each side is also an option.
The rest can have a relaxed profile tolerance overall, but you may want to make it easier and have separate, as in SEP REQT, applied to the plan view profile and the side view profile of the handle as it relieves having to make a 3D fixture to lock in the part. The result should not be different but it may relax some arguments about how tough it would be.
Not sure how to handle the undimensioned geometry - unless the drawing says the model is the source of all dimensions not included on the drawing.
Secondly, the item that is functional is the width of the slot. The valve can be operated with channel locks. The tab is serving to stop people from going too far and closing the valve.
Mainly I would indicate a small area as a datum target area where the handle fits flat on the valve as the primary datum feature, with a flatness applied to that area, the narrow width of the slot as the secondary at MMC, with a perpendcularity to the primary datum feature and the length of the slot as the tertiary feature at MMC, also with a perpendicularity to primary datum feature.
The sides of the tab need to have a better control than all the rest, maybe a position tolerance on the width of the tab. Profile on each side is also an option.
The rest can have a relaxed profile tolerance overall, but you may want to make it easier and have separate, as in SEP REQT, applied to the plan view profile and the side view profile of the handle as it relieves having to make a 3D fixture to lock in the part. The result should not be different but it may relax some arguments about how tough it would be.
Not sure how to handle the undimensioned geometry - unless the drawing says the model is the source of all dimensions not included on the drawing.
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