Has anyone ever seen a print that has 5 A datum targets (or just more than 3) and use the extra as constrained points with a tolerance? If so, could you provide a picture of how it is called out on a print?
Usually if I see a tolerance on the A datum points, it's a (circled F) free state check prior to clamping. Otherwise, Datum A is Datum A. There is no tolerance, because it's datum A. But, in real life, parts aren't perfect. Depending on how you are measuring the parts, you might see more deviation. If you have a good fixture, you should be hitting +/- 0.05mm easily. On a custom standoffs setup, I'm able to hit +/- 0.10mm mostly (depends on what tools you have at your disposal, .005" is the best I have for fixed height changes).
If it's not specifically called out, your tolerance is technically half of whatever the surface tolerance for that surface is (positive only, since a Datum A should theoretically never be negative, while the surface profile around it can be bilateral).
Usually if I see a tolerance on the A datum points, it's a (circled F) free state check prior to clamping. Otherwise, Datum A is Datum A. There is no tolerance, because it's datum A. But, in real life, parts aren't perfect. Depending on how you are measuring the parts, you might see more deviation. If you have a good fixture, you should be hitting +/- 0.05mm easily. On a custom standoffs setup, I'm able to hit +/- 0.10mm mostly (depends on what tools you have at your disposal, .005" is the best I have for fixed height changes).
If it's not specifically called out, your tolerance is technically half of whatever the surface tolerance for that surface is (positive only, since a Datum A should theoretically never be negative, while the surface profile around it can be bilateral).
Some of the fixtures I get that have more than 3 "A" datums will have what I call 'drop nets' when they want a free-state check on the 4th, 5th, etc. "A" targets. Pull a lever, the net drops (3mm or more) so you can get the full +/- tolerance. Load the part with all nets 'up', clamp 1, 2, 3, drop all the drop nets, check 4, lift & clamp,check 5, left and clamp, etc.
