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.
]So in my case slot, which should be at -4.5, -17 is at -3.7, -17.15 when rotation is based on L axis[/B]. Using 4.5 offset puts -3.7 at perfect -4.5 and makes -17.15 very close to -17 so position is good? Now, if the slot was at -3.7, - 16.85 instead (moved to the right and 0.15 up instead of to the right and 0.15 down), using 4.5 offset would make -16.85 even shorter and position out (let's assume hole and slot are the minimum allowable size so there is no extra bonuses)? I don't see the difference.
No. Your slot is not at -3.7. Forget that you ever did that.
Your slot has an
offset basic of 4.5.
That is where your slot is. Its location along the 17 axis is
controlled by a separate FCF to
ABC.
]So in my case slot, which should be at -4.5, -17 is at -3.7, -17.15 when rotation is based on L axis[/B]. Using 4.5 offset puts -3.7 at perfect -4.5 and makes -17.15 very close to -17 so position is good? Now, if the slot was at -3.7, - 16.85 instead (moved to the right and 0.15 up instead of to the right and 0.15 down), using 4.5 offset would make -16.85 even shorter and position out (let's assume hole and slot are the minimum allowable size so there is no extra bonuses)? I don't see the difference.
No. Your slot is not at -3.7. Forget that you ever did that.
Your slot has an
offset basic of 4.5.
That is where your slot is. Its location along the 17 axis is
controlled by a separate FCF to
ABC.
