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.
Thank you. Except your graphics are based on slot actually located at 4.5, -17. If the slot is at 3.7, -17.15 when squared, than after rotating to 4.5 offset line it will be skewed in relation to the rest of the assembly and this part will never pass hard gauge which would be: one pin simulating B at MMC of the hole and another pin with the shape of the slot and size of L (MMC) - 0.25, W (MMC) - 0.25. There is only 0.02 bonus from B and size of the slot is only bigger than it's MMC by 0.02 in L and 0.02 in W. Centers of the 2 pins would be at exact basic distances from the drawing.
Thank you. Except your graphics are based on slot actually located at 4.5, -17. If the slot is at 3.7, -17.15 when squared, than after rotating to 4.5 offset line it will be skewed in relation to the rest of the assembly and this part will never pass hard gauge which would be: one pin simulating B at MMC of the hole and another pin with the shape of the slot and size of L (MMC) - 0.25, W (MMC) - 0.25. There is only 0.02 bonus from B and size of the slot is only bigger than it's MMC by 0.02 in L and 0.02 in W. Centers of the 2 pins would be at exact basic distances from the drawing.
I suppose there's a question we've overlooked. What is master? The print, or CAD?
If the print is master, then:
The slot
can't be 3.7 in the X direction. The print defines the location of the slot in the locating direction as 4.5. Not the other way around.
If your gage is built with a slot shaped locator,
it's wrong. The GD&T defines a DRF which rotates to the major axis of the slot. It should be a two-way locator in the length axis.
If CAD is master, then:
The slot
still can't be at 3.7 in the X direction, because, again, the location of the slot in the alignment direction is defined, not by the part, but by the GD&T. So, it would be at whatever it shows to be in CAD.
In CAD part is only squared in Z but slot is skewed in relation to X and Y. I can see your point about two-way locator. I was just simply going by ASME Y14.5M 94 GD&T standard which, for noncircular features at MMC states:
In terms of the boundary for an elongated feature. While maintaining the specified size limits of the elongated feature, no element of its surface shall be inside a theoretical boundary of identical shape located at true position. The size of boundary is equal to the MMC size of the elongated feature minus its positional tolerance.
I guess at the end it still comes down to interpretation of the print. To me what defines direction is slot L axis and 4.5 is only to be used for TP evaluation, specially that there are 2 TP callouts of the slot. Using 4.5 offset and evaluating only center makes perfect TP for one of those callouts.
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.
The way the Slot Position works is the midpoint. The Midpoint along a single axis. The 0.25 AB True Position in example represents deviation of 4.5 Basic axis only (Length of slot is defined by brackets)
The second direction along the 17 Basic would need to be defined and in a Slot typically is with a second Position FCF defined with Basic 17 or an angle basic Polar etc.
yes True position could be in tolerance with form that along the second axis rotated described.
Will part function?
Is there more geometry on drawing that constrains slot?
This isn't a slot with a boundary TP. This is a slot that is Datum C in one axis, and has a separate FCF for the other axis. In fact, you shouldn't even think of it as a slot. It's a feature that, as Rich said below, is a midpoint on one axis, and a midplane on the other axis.
Is there more geometry on drawing that constrains slot?
This is it.
The way the Slot Position works is the midpoint. The Midpoint along a single axis. The 0.25 AB True Position in example represents deviation of 4.5 Basic axis only (Length of slot is defined by brackets)
Does this mean that, if let say, slot L axis should be parallel to the bottom edge of the part but is suddenly rotated 45 degrees, as long as it's center is still at 4.5, -17 from B it's position is perfect?
No, because you still have to meet the position of the slot's width. The slot width has a TP, this TP is what is controlling the orientation of the slot, to A|B|C.
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. 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.
]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.
