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.
It has a diamond pin and I agree with you. All I am saying that 1 of the 2 parts stopped fitting (it actually has to fit inside injection mould not a fixture). Punch making this part was loose. But when the part is measured with offset alignment, position along W axis is still good because it is shorter axis (and actual slot is off more to the right than down). Points at the end of L axis are no good but they are not checked, only center along L is checked showing perfect position since it is based on offset from the drawing.
Ok then. First, inspect the part to the datum structure. If the slot
is shifted, then the entire rest of the part
should fail.
After it fails, you go back and add more data where needed to prove that C is the failure point.
How do you know that "Points on the end of L axis are no good" if they "are not checked"? If you are only checking a single point on the width of C, of course you won't be able to prove that the slot is shifted. Like I said, If you're trying to prove what is failing, then you need more data.
Measure 3 sets of opposed points. One set towards each end, and one set in the middle. If you are right about the slot, the sets of points on the ends should fail. Viola, there's your proof.
The center point of the width can also potentially fail, if the slot is shifted far enough right/left.
It has a diamond pin and I agree with you. All I am saying that 1 of the 2 parts stopped fitting (it actually has to fit inside injection mould not a fixture). Punch making this part was loose. But when the part is measured with offset alignment, position along W axis is still good because it is shorter axis (and actual slot is off more to the right than down). Points at the end of L axis are no good but they are not checked, only center along L is checked showing perfect position since it is based on offset from the drawing.
Ok then. First, inspect the part to the datum structure. If the slot
is shifted, then the entire rest of the part
should fail.
After it fails, you go back and add more data where needed to prove that C is the failure point.
How do you know that "Points on the end of L axis are no good" if they "are not checked"? If you are only checking a single point on the width of C, of course you won't be able to prove that the slot is shifted. Like I said, If you're trying to prove what is failing, then you need more data.
Measure 3 sets of opposed points. One set towards each end, and one set in the middle. If you are right about the slot, the sets of points on the ends should fail. Viola, there's your proof.
The center point of the width can also potentially fail, if the slot is shifted far enough right/left.
