Hello, have been reading this forum for a while now, great source of information. Recently question came up about measuring method so I would like to get advise from the experts. Based on the drawing datum A is the surface of the the stamped part, datum B is is a hole without any positional tolerance and than there is a round slot. Length and width of the slot are dimensioned separately. Length of the slot is marked as datum C and has non diametrical TP 0.25 MMC, A, B MMC with the associated basic dimension of let say 4.5 mm in X direction (looking at the drawing length is in X and width is in Y). Width of the slot has also non diametrical TP 0.25 MMC, A, B MMC, C MMC with the associated basic dimension of let say 17 mm in Y direction. Both hole and the slot are on the same plane A . At some point insert stopped fitting so measurements started at both ends (our company and supplier). My results were showing TP out with center of the slot being only 3.7 mm in X and 17.15 in Y. Company which makes inserts admitted their punch was loose but said position is still in spec. I was setting alignment by measuring 2 radiuses of the slot, creating line between their centers and rotating alignment to it, they simply used 4.5 mm basic to create offset alignment which also automatically made 17.15 in Y shorter and almost perfect. They are also reporting TP of the slot's center in only one direction since in the other direction would be perfect based on the offset. I presented position in 2 directions (thanks to all the posts regarding generic features and variables), also tried explaining that TP callout is not only for the center but any point along slot's axis. I need some confirmation or correction to my method.
Create 2 generic circles. One that has a diameter from the slot length and one that has a diameter from the slot width.
Dimension TP the X axis and D of the slot length. (Yes, this will be 0. The only deviation you could get would be if it was not perp to A, if it is a slot with significant depth.)
Dimension TP the Y axis and D of the slot width.
Thank you guys. So I understood correctly your method.. One position will be perfect and only center is being evaluated (dimensioning TP of slot width evaluates only center point in Y so even slot at 45 degrees in relation to how it should be and perfect center location will show good position). I guess I am in square one.
The TP on slot width controls the clocking of the slot. If you think you need to, you can construct a set of mid-points along the slot width to show if it is out of tolerance.
If you want to do that, do 3 sets opposed points, one set in the middle, and one set towards each end. Create mid points and dimension those in Y. They should all be 17 +/- half of TP tolerance.
The TP on slot width controls the clocking of the slot. If you think you need to, you can construct a set of mid-points along the slot width to show if it is out of tolerance.
If you want to do that, do 3 sets opposed points, one set in the middle, and one set towards each end. Create mid points and dimension those in Y. They should all be 17 +/- half of TP tolerance.
