Bidirectional tol. vs 2 single segment feature control frames
Bidirectional tol. vs 2 single segment feature control frames
(OP)
Can anyone explain the difference between controlling the position of an FOS with a bi-directional tolerance vs. a 2 single segment feature control frame (non-diametric)? Both indicate direction and magnitude relative to specific datums. What are the benefits of one method over the other?





RE: Bidirectional tol. vs 2 single segment feature control frames
One will have a FCF reflecting the length and one reflecting the width.
A single segment FCF is altogether different. The top section or 1st level reflects the position of the pattern relative to the datums such as A, B and C. The secondary or lower level FCF reflects inside the pattern. The lower section may only reflect datum A and B. Datum A usually relates to orientation (perpendicularity) while datum B is dimenioned and oriented to that datum.
Hope this helps.
Dave D.
RE: Bidirectional tol. vs 2 single segment feature control frames
I hope that I understood your question. I think I did.
RE: Bidirectional tol. vs 2 single segment feature control frames
(1) a bi-directional tolerance provides an equal tolerance zone in two directions (wrt the datums) from the basic position of the FOS
(2) two single-segment positional tolerance FCFs specify a different tolerance in each of the two directions (wrt the datums) from the basic position of the FOS
Here's a couple of scenarios;
(1) a tapped hole in a plate must align with a square or circular clearance hole in another plate so that the fastener can move equally in any direction from the basic position; equal bi-directional tolerance would be suitable here
(2) a tapped hole in a plate mates up with a slotted hole in another plate so that the two plates can only move in one direction wrt each other; you would want a looser tolerance in the direction of the slot, but tighter perpendicular to the direction of the slot
Jim Sykes, P.Eng, GDTP-S
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