CLARIFICATION on TRUE POSITION callout

[dfiola66]

3 8mm holes on -A- surface, one of which is -C-. -B- is 12.7mm hole on another surface.

The feature control frame calls out the other 2 8mm holes @ TP .5 max material to -C- only...no other datum callout in the frame.

In my program, I make -C- my xyz zero, but leave my alignment alone since theres no alignment stated in the FCFrame and measure and tolerance the 2 holes to the .5mm TP.

Does this sound right....reason I'm asking is the gage shows the holes to be good (to themselves...pattern check) yet the program is showing them to be way off.

[J Temmen]

You set X,Y,Z origin on [C] but what are you rotated to? Is there a diameter symbol in the FCF? If not, I would align between [C] and Hole #1 and TP the distance to hole #1, then do the same for hole #2. If there is a diameter symbol in the FCF then rotate to [C] and hole #1 then rotate nominal angle and TP both axis, again, same for hole #2.

[dfiola66]

You set X,Y,Z origin on [C] but what are you rotated to? Is there a diameter symbol in the FCF? If not, I would align between [C] and Hole #1 and TP the distance to hole #1, then do the same for hole #2. If there is a diameter symbol in the FCF then rotate to [C] and hole #1 then rotate nominal angle and TP both axis, again, same for hole #2.

Rotated to the original ABC alignment (car position). They are obviously wanting these three holes to be held close in the pattern to -C- but since no other datum was inserted in the FCF, then I left it on the original alignment.

Yes, theres a diameter symbol there. Rotating to -C- is the original alignment (iterative...car position) which when I dimensioned the TP, I didn't change.

callout looks like attachment.

[J Temmen]

The CMM is checking the part one way while the fuctional gage is checking something else,I thought you wanted both to read the same result. If you do then the CMM has to act like the gage and not tie into [B].

[dfiola66]

The CMM is checking the part one way while the fuctional gage is checking something else,I thought you wanted both to read the same result. If you do then the CMM has to act like the gage and not tie into [B].

Agreed and understood and that's the problem.

Based on the callout, in your opinion, is there enough gd&t information to correctly measure and tolerance those holes? In my interpretation, all the FCF tells me to do is move my XYZ datum to -C- and nothing else.

[Paul Barriage]

Dave,

From your pic, it looks as if the tolerance called out is more of a pitch than anything else. Change the work plane to that which would "see" that dimension before you do the true position. Then just dimension that axis that is referenced by -C-.

[J Temmen]

If it were me I would dimension it without any relationship to [B], just the spread beteween [C] and feature, just like the gage.

[Jeffrey Lovely]

When programming always - Think like a gage

[Schrocknroll]

Since there is only one Datum, establish X and Y (assuming your holes are normal to the Z axis). Then you are free to rotate around the -C- axis until you find the best condition for the holes. You may want to try a best fit alignment, with rotation only, using the 3 8mm holes.

[Jeffrey Lovely]

plus you have the gage in front of you !
print call outs dont always match the gage
I include this to cover my #%^$
Measured Dim#xx as gaged on fixture #xxxx

[Schrocknroll]

When programming always - Think like a gage

Within the constraints of the FCF.

[dfiola66]

Dave,

From your pic, it looks as if the tolerance called out is more of a pitch than anything else. Change the work plane to that which would "see" that dimension before you do the true position. Then just dimension that axis that is referenced by -C-.

Hey Paul,

True...and that's another avenue. There are boxed dimensions on the print between the 3 holes. I could make the surface my normal or working plane and make -C- my origin, but in order to match the print boxed dimensions, I'd have to reorient the part from car position.

This pic may help. Left most hole is -C- and 2 holes right are in question. Trihedron shows car position. Basic dims on print are parallel to triangled cutout in part, not to axis in car positon therefore, when I move XYZ origin to -C-, I still won't get the correct numbers (I'd need to rotate the part).

[Jeffrey Lovely]

yes
sometimes I get so wound up that if Im not restrained (FCF)
I start spinning uncontrolably
like an epileptic v brator

[Cumofo]

Hey! Easy on my ears please. Ok the origin is to datum C(fixed), but the rotation is soley to the hole pattern itself(free). So rotate to a line between the two holes in the pattern, and wash your mouth out with soap.

[KillGorack]

I may not know how to do this correctly, however we have some GD&T like this. What we do is keep alignment normal to ABC, Just origin to what ever your tertiary or C axis, and just dimension that feature in that axis only. or a par to axis distance would give you the same thing right? like what Paul Barriage said?