Gd&t True Position

[jessejames]

OK we have a FCF that has a diameter callout an true position to Datums A B C
when generating the report an doing the tolerancing would you output to 2 datum features or 3 datum features.we are have a discussion about this an i am saying that if you call out TP to 3 datums on the print thats how i will report it,if you want it to 2 datums that call TP in FCF to Datums B an C right or wrong. thx

[Matthew D. Hoedeman]

OK we have a FCF that has a diameter callout an true position to Datums A B C
when generating the report an doing the tolerancing would you output to 2 datum features or 3 datum features.we are have a discussion about this an i am saying that if you call out TP to 3 datums on the print thats how i will report it,if you want it to 2 datums that call TP in FCF to Datums B an C right or wrong. thx

If you are already aligned to ABC, just simply report TP without the use of the datums. That is a whole kettle of fish that just stinks!

[Snaggy]

If the call out is for 3 datums then I would report to 3, if it was for 2 then I would report to 2. Do what they ask for and you can't be wrong, CYA.

[wicked_tattoo]

I am with snaggy, but matt makes a good point. If it were me though I would go with all 3 if that is what it asks for.

[Jan d.]

What version do you use?

If you use V4.0+ then use XactMeasure tolerancing. It's easy and quick. If the FCF calls for 3 datums, you have to evaluate against those 3. No way around it.


Jan.

[John Kingston]

Three datums for a TP FCF is legal. It adds control of the entire length of a cylinder (ie, perpendicularity). This eliminates the need for 2 FCFs.

[jkb_mcg]

Yeah, but, when you include 3 features with your reference feature at MMC and another at MMC, 9 times out of 10, your deviation is .000. due to the fact of it borrowing from the MMC to make the best fit.