Query on true position geometric tolerance

[Bob Fairbrother]

I have just been trying to get my head around a true position geometric tolerance for some holes that references 4 (yes 4) Datum features.
These holes are machined perpendicular to a face (Datum A) and
positioned to centrelines (Datums B and C)

Datum Description
A Face
B Centreline of main bore
C Centreline of main bore @ 90° to B

No problems so far, but the then the geometric tolerance calls up Datum D which is a group of 4 holes machined in the same face

I think the draughtsman has got it wrong and there should be 2 seperate geometric tolerances.

The first one referencing Datums A B C
The second on referencing Datum D

Then I would report the holes twice, first time to Datums A B C, second time to Datum D.

Any thoughts?

Bob Fairbrother

[why me]

is this an extruder barrel? I have seen this in the past and I reported the true position to each datum ABC then to D

[tking]

I have just been trying to get my head around a true position geometric tolerance for some holes that references 4 (yes 4) Datum features.
These holes are machined perpendicular to a face (Datum A) and
positioned to centrelines (Datums B and C)

Datum Description
A Face
B Centreline of main bore
C Centreline of main bore @ 90° to B

No problems so far, but the then the geometric tolerance calls up Datum D which is a group of 4 holes machined in the same face

I think the draughtsman has got it wrong and there should be 2 seperate geometric tolerances.

The first one referencing Datums A B C
The second on referencing Datum D

Then I would report the holes twice, first time to Datums A B C, second time to Datum D.

Any thoughts?

Bob Fairbrother

Bob,

Any basics from -D- to the holes? Wondering if the A/B/C is for alignment and maybe the center of the -D- pattern is origin.

Just thinking. Kbotta can help on this, my bet.

TK

[Paul Barriage]

Possibly look at it this way.

The boss says, "Mount the durn wheel, I don't care if it had to be 1 inch off position to balance the deck."

So, hence, the TP to the bolt pattern is greatly important, while the position to A/B/C is not so inflexible.




Remember, if it doesn't fit, FORCE IT. If it breaks, it needed replacing anyway.

[Jeffrey Lovely]

Normally there is a tighter tolerance to D
Would the part be good to D if its ok to ABC using the same tolerance?