In this video, Brandon compares a Composite Feature Control Frame and a Multiple Single Segment Feature Control Frame to show the effect of each on Position tolerance.

What is a Composite Feature Control Frame? 

A Composite Feature Control Frame (FCF) contains two tolerance zone frameworks. It is shown to be a composite tolerance because there is one geometric symbol that spans across the two frameworks. Figure 1 shows a Composite FCF controlling Position tolerance of a pattern of holes. The tolerance indicated by the upper control frame is shown in green. The tolerance indicated by the lower FCF is shown in red. 

Note: for all images below Datum A is the back side of the part. This is simply not shown to reduce the width of the images.  

Figure 1: Composite Position Feature Control Frame (Datum A is the back side of part)

The top frame is the Pattern Locating Tolerance Zone Framework (PLTZF), which is pronounced “plahtz.” The PLTZF locates the pattern to the datum reference frame and is going to be a more generous tolerance. It behaves the same as a normal position tolerance.

The bottom frame is the Feature Relating Tolerance Zone Framework (FRTZF), pronounced “fritz.” This framework refines the location and orientation of the pattern itself. Meaning, for our example, the FRTZF refines the location and orientation of the holes only in relation to each other.

Another characteristic of the Composite FCF is that the bottom frame must match the top frame. In the Figure 1 example, the top frame locks location and orientation of the pattern to datums A, B, and C. The bottom frame locks the orientation of the pattern to datum A and the rotation of the pattern to datum And B. You can see that the datum callouts in the bottom frame align under the matching datum callouts in the top frame. What if it was not necessary for the pattern to lock to datum B, but locking to datum C was required? For the bottom frame to match the top, datum C could not be placed under datum B. All three datums would have to be called out in the bottom FCF, even though datum B would not be used.

In summary, there are four Composite Feature Control Frame rules:

  1. The Position symbol must span across the two frames.
  2. The bottom frame (FRTZF) refines the location and orientation of the holes only to the other holes.
  3. If datums are called in the FRTZF, it only refines orientation to the specified datum(s), not location.
  4. The bottom frame must match the top frame.

What is a Multiple Single Segment Feature Control Frame?

A Multiple Single Segment (MSS) Feature Control Frame (FCF) also contains two tolerance zone frameworks. However, the two frames are completely independent of each other.  The position symbol is shown on each frame, rather than having a shared symbol as in the Composite FCF. Figure 2 shows a Multiple Single Segment FCF for the same part shown in Figure 1.


Figure 2: Multiple Single Segment Feature Control Frame (Datum A is Back side of part)

In a Multiple Single Segment FCF, the top framework is the same as the top framework for the Composite FCF.

The difference between Composite and MSS feature control frames comes into play in the bottom framework. In the Composite FCF, the bottom framework only refines the orientation of the pattern to any referenced datums and the location to itself. In the MSS feature control frame, the bottom framework refines both the location and orientation of the top frame.

Another difference between Composite and Multiple Single Segment FCFs is that the bottom frame of the MSS feature control frame may call out any datums in any order – unless it is an exact copy of the top datum. Because the top and bottom control frames in a Multiple Single Segment FCF are completely independent, an exact match of datums on the bottom frame would cause redundancy. This would cause the bottom frame to wipe out the requirement in the top frame altogether because the bottom frame has a tighter tolerance.

A Multiple Single Segment Feature Control Frame has the following rules:

  1. Both Feature Control Frames are completely independent.
  2. The bottom frame refines the location and orientation of the top frame.
  3. The bottom frame can have any datums in any order but cannot be a repeat of the top frame.

How is Tolerance Affected by Using these Feature Control Frames?

Let’s look at how using a Composite FCF versus a Multiple Single Segment FCF affects the tolerance.

In Figure 3, the same part is shown using a Composite FCF callout on the left side and a Multiple Single Segment FCF callout on the right side.

Figure 3: Composite Tolerances vs. Multiple Single Segment Tolerances (Datum A is Back side for both parts)

The part shown on the left side in Figure 3 calls out a Composite tolerances. The Ø0.2 tolerance zones in the bottom frame are locked to each other with basic dimension but are allowed shift within the Ø0.8 zones; They are allowed to shift in any direction, as the lower frame is only keeping the pattern from rotating and orientated to datum A.

The part shown on the right side in Figure 3 calls out Multiple Single Segment tolerances. With datum B listed in the bottom frame, the red Ø0.2 tolerance zone is locked to the basic dimension of 20. This results in a “slotted” tolerance zone. The tolerance zone can move from left to right from that basic dimension of 20 but cannot shift in any other direction.

As you can see in this example, with the tolerance values and referenced datums being the same between the Composite and Multiple Single Segment Tolerance frames, the Multiple Single Segment FCF results in a tighter tolerance. This is because the MSS frames are independent, and the bottom frame refines location and orientation of the top frame, where the bottom frame of the Composite FCF only refines the location of the holes to the other holes in the pattern and orientation to any datum referenced.


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