Can a Datum feature reference itself in Y14.5M (GD&T)?
Can a Datum feature reference itself in Y14.5M (GD&T)?
(OP)
If I have a part with 3 datums, datum A is the surface on which I have datum B - a hole and datum C - the width of a slot and I want to tolerance the length of the slot can I use a positional tolerance that references A|B|C or can I only use A|B because the slot is C?
If I do tolerance the length to A|B|C what would that physically mean? How could the length of the slot vary, positionally, with respect to the width of the slot?
Thanks,
J
(Originally posted in ANSI standards forum)
If I do tolerance the length to A|B|C what would that physically mean? How could the length of the slot vary, positionally, with respect to the width of the slot?
Thanks,
J
(Originally posted in ANSI standards forum)





RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
Your datum C controls the rotation of your part. Until this is controlled, there is no rotational datum. Your slot's width is controlled by Datums_A and_B. Once the slot is in place, you have three datums.
If there was a feature you could use to control your slot, *it* would be datum_C, wouldn't it? :)
JHG
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
J
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
Imagine if you were dimensioning a different slot. You could give each dimension (width and length) its own positional tolerance. No difference. Completely legal, just not common. Don't forget to omit diamter symbol.
http://www.EsoxRepublic.com-SolidWorks API VB programming help
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
Slots which mate with a floating or fixed fastener are handled in special way and you should be aware of this method. It's called a 'Boundary' condition (pg 143) which just takes into allowance the special shape and possibly different tolerances to define the feature's virtual condition. If the function of the width of the slot is a mating or aligning and the next important feature then it MUST be chosen as a datum to locate other features that are connected in someway so as to imply their intended purpose too.
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
Picture that the slot position is constrained along the slot centerline (the line symmetrical between the two linear portions). The entire slot can "slide" along that line until it is constrained by another dimension and tolerance.
RE: Can a Datum feature reference itself in Y14.5M (GD&T)?
This with regards to plane C as the orienting feature.