True Postion

[B. Jacobs]

:confused: I am still trying to figure out this true postion stuff. I hav a square part that is 3.8in long by 1.4 in wide. There are two circle spaced 1.88 apart. I have a true postion callout I think. The 1.88 dim is basic. In the GD&T box there is o circle with crosshair then .030 dia. Thats it.

Couls someone explain this to me. What am I checking.
Thanks in advance

[B. Jacobs]

Here is a sketch that might help

[kbotta]

Is there a DRF (datum reference frame) ref at the end of the feature control frame (FCF)?
Are there datums identified on your drawing?
1 last thing, could you post a more detailed pic of the drawing?
Thanks,
Kevin

[B. Jacobs]

This is what it looks like. Unfortunitly thats it. I drew the best I could. Hope this helps.

[george frick]

the way i would check it is to align the 2 dias to each other. origin 1 dia. and check the 1.880 dim. theres not much more to the sketch. basically you have a 1.880 +/-.015 dimension

[BSchwark]

I agree with George. Align using the 2 diameters, Origin on 1 diameter and report the other one. You could than use your position tolerance and answer the TP call out X=0 Y=1.880. Or a down and dirty way to do it is check the distance between the two diameters and double the difference of your measured from the basic and you will get your true position answer.


BS

[bob mappes]

This is a definate case where the person who drew and toleranced this part knows that GD&T exists but DOES NOT know how to apply it to a drawing.

myself, I would align off the two "zero" sides of the block, pick up the holes and apply the TP callout.

TP of .030" is pretty wide open anyways, unless this is in mm and then its a wee bit tighter....

bob

[tking]

I agree with George as well. Word for word.

TK

[B. Jacobs]

I did what Goerge said I think. Here is my alignment.

=ALIGNMENT/START,RECALL:DCC-ALN, LIST= YES
ALIGNMENT/LEVEL,ZPLUS,CIR1
ALIGNMENT/ROTATE,YPLUS,TO,CIR1,ABOUT,ZPLUS
ALIGNMENT/TRANS,XAXIS,CIR1
ALIGNMENT/TRANS,YAXIS,CIR1
ALIGNMENT/TRANS,ZAXIS,CIR1
ALIGNMENT/ROTATE,YPLUS,TO,LIN4,ABOUT,ZPLUS
ALIGNMENT/END

This seemed to get the answers I was looking for. Now I am doing TP to circle two. By the way Cir1 is the top cir. and line 4 is right side of part.

[tking]

email me with your phone # if you'd like, it'll take about 3 minutes to walk you through this.

TK

tking@lear.com

[John Kingston]

Like all have said, not the best use of TP. Typical, but wrong.:cool:

[B. Jacobs]

I was just given another one. I wish they knew how to do these TP things. This time it is 4 holes. Same GD&T box as before but instead of .030 it is now .014. I am trying all sorts of things.:mad:

[DaddyBluto]

Is there a block in the corner that says reference X|Y|Z unless otherwise specified and/or datums called out on the drawing anywhere? Quite a few of the drawings I get have the "block tolerance" application. Dang lazy design engineers.

Jaime

[BSchwark]

Get the ASME Y14.5-1994 Dimensioning and Tolerancing Book. Maybe an engineer in your company may have it. Or get Geo-Metrics by Lowell W. Foster.
It is a book for the application of GD&T techiques


BS

[John Kingston]

I'd take it back to Engineering and ask what my datums are. Where is X,Y,Z zero point. That is where all the measuring should start from. A drawing is supposed to communicate the Engineer/Customer needs. Give'em what they ask for , prove it, then show them the "proper" way to ask for it. ;)