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.
In your first post you said that length is clocking, now you are saying width? As for the rest, isn't that what I said earlier that all the points along each axis should be within +/- 0.125? Doing 4.5 offset makes slot skewed and points at the end of L axis are outside +/- 0.125. I feel like we are going in circles here.
No. You're mixing things up.
1) The hole and slot length are your rotational constraint. The two, together, stop the rotation of your DRF.
This happens BEFORE you check the TP of the width (aka, the clocking of the slot).
2) The TP of the width controls the clocking
of the slot. To pass the TP of the width, yes, all opposed points would need to be +/- 0.125, but
you don't base your DRF on that! You check to see if it's right
after you're set your DRF.
These are two completely separate things.
Yes, this does mean that if the slot is at a 45 degree angle from how it should be, that it won't measure very well
because that means the part is BAD! It doesn't mean that something is wrong with the print.
In your first post you said that length is clocking, now you are saying width? As for the rest, isn't that what I said earlier that all the points along each axis should be within +/- 0.125? Doing 4.5 offset makes slot skewed and points at the end of L axis are outside +/- 0.125. I feel like we are going in circles here.
No. You're mixing things up.
1) The hole and slot length are your rotational constraint. The two, together, stop the rotation of your DRF.
This happens BEFORE you check the TP of the width (aka, the clocking of the slot).
2) The TP of the width controls the clocking
of the slot. To pass the TP of the width, yes, all opposed points would need to be +/- 0.125, but
you don't base your DRF on that! You check to see if it's right
after you're set your DRF.
These are two completely separate things.
Yes, this does mean that if the slot is at a 45 degree angle from how it should be, that it won't measure very well
because that means the part is BAD! It doesn't mean that something is wrong with the print.
