Strange Datum Targets Advice Welcomed!!!!

[zoolander303]

So, this datum target scheme I've never seen layed out this way before for datum D, I was going to go iterative for alignment, then what I was going to do is fixture the part on standoffs on datum A surface for my Z, then use B as my X origin and C as my Y origin. They dont require any callouts to datum D so I thought that was odd, as far as defining datum D I was going to use a 3mm ruby, measure a circle around the O.D. and then create theoretical points in the 4 target locations, but kinda confused on why they have this in here if nothing is relating to it in the FCF's, wondering what you guys think for tackling this or how you would align to datum D if you needed too???

[UKCMM]

Not sure why you do not just take the target hits as marked on the drawing why complicate things with making theoretical points from a circle.

[marcc]

B would be my X,Y origin, C stops rotation with 22.5 degrees offset alignment, 4 points at 0, 90, 180 and 270 degrees make datum D. Check other views, sections for D being called.

[zoolander303]

D isnt called out in any other views, I think D might be how they want the part fixtured for measuring???? What do you think, I dont know how id fixture that one

[MikeD6]

What is datum A?

[bfire85]

Align to A B and C. Pretty simple. Use the 4 target points to measure Datum D as a circle. If Datum D isn't used in a FCF anywhere on the print, then ignore defining it, or go back to the customer or engineering and see if they missed something. I have seen Datums called out on a print that are referenced to another drawing for an assembly.

[zoolander303]

I took A as a plane leveled to zplus, then took b as a circle for my x,y origin, then c i also used a circle but when i rotate to xplus 22.5 it spins my cad, so i made a line from C to B and rotated that 22.5 degrees offset and it didnt spin my model, how would you go about that issue if I didnt want to use a line?

[zoolander303]

B would be my X,Y origin, C stops rotation with 22.5 degrees offset alignment, 4 points at 0, 90, 180 and 270 degrees make datum D. Check other views, sections for D being called.

I tried that and its spins my trihedran im using a auto circle for C, if i construct a line from C to B and offset align that by 22.5 then it doesnt spin my cad or trihedran

[louisd]

If Datum D isn't referenced at all on the print, it could be used to clarify how they expect you to measure that feature of size Ø423 ±1 [TP][Ø1][A][B][C] on its own.

Or it could just be remnant crap from a drawing revision that was done by someone who had no idea what they were doing.
--They likely removed a FCF reference to D, and didn't remove the datum targets. (this is where i would place my bet)

as far as ABC align:
Construct a line between B and C centroids

Level A to Z axis.
Rotate to BC line about Z
Translate Z to A
Translate X & Y to B
then Rotate about Z -22.5° to take your four D target hits.

Like marcc said, make sure D datum target points don't have a defined location (depth from A datum) in another view. if so, be sure to take your hits relative to that basic offset from A.

[zoolander303]

YEAH!!!, that worked nice thanks louisd