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True position of... length?

Erikir
I have a round slot, 17 mm from edge of radius to edge of radius and 4mm wide.

My drawing says
17 +/- 0.3
|TP|0.5 MMC |A|B|C| (length)
Boundary

4+/- 0.3
|TP|0.2 MMC |A|B|C| (width)
Boundary

How do I report that?
  • I run into slots using TP (Ø in the FCF tol. box) at times, and TP them as mentioned in the thread because I am told to. I do not think a slot should be TP, based on the different size of the width and length tol., not to mention the pos. tol. difference. Maybe someone can answer this, if you TP a slot in one axis, would not the TP formula figure out the location in a diametrical zone, possibly impeding into the other axis, making it possibly out of tol.? I was told by my GD&T instructor, slots should be basic dimensioned due to their function. As the Tec note shows, two separate positional call outs with no Ø symbol in the tol. box. My understanding of this means ±. Am I misunderstanding this? Or when a slot is TP, the person that made the print made an error? I always let the powers that be tell me what they want and report as such, but it would be nice to have a clear understanding.
  • The thing is to unselect the "Ø" in the XactMeasure FCF builder and choose the vector to evaluate the TP in by clicking "Planar zone". Make sure you select the correct axis under the "Advanced" tab in XactMeasure as well. That way, the TP should be calculated using one axis and ignoring the others. And yeah, if you boil it down, it really is the basic dimension ± the TP tol / 2.

    I agree with Obelix though, that tolerancing the two halfcircles of the slot would make it (a lot) easier.

    I get one-axis TP on slots that are MMC, rotated and whatnots and that can take quite a lot of work to get right (programmatically).

    It's up to the designers to tolerance the slot correctly. If you follow the print, noone can blame you for following it, right? The designer can't say "Well, my intention was..." because the print should reflect his intentions.
  • Advantage of TP in one axis(vector) over +/- dimension is MMC/MMB
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