Aha: the scissor-arm. A IK-puzzle to enjoy
The difficulty is mainly that IK relies on a linear hierarchy of objects, whereas at first site a grid is needed for structures like the scissor-arm. Alas : one object = one pivot!
IK isn’t “breaking” (as you say), it acts properly. Indeed Object 23 is child of hinge Object 30, but its own (Bongo-) pivot lies all the way down at the end. Since it is a Hinge is will indeed rotate but it will rotate there, at the end, and not where you want (in the middle). So Object 23 will indeed apparently freely rotate ‘away’ from its parent.
Solution is to release Object 23 from all the IK properties and move its (Bongo-)pivot where you expect it to hinge : at its middle – on top of Object 30. Then, in order to constrain Object 23 at its end an auxiliary object is needed : Object 25 can serve. Make it child of Object 23 and constrain it to its location.
scissor-extended-02 001.3dm (127.2 KB)
PS In fact Object 30 can be omitted. Now that its pivot is at the right spot Object 23 can be directly a Hinging child of Object 22.
Just thought of another even simpler solution to rescue you model. It will work fine when you make Object 23 only a constrain but no longer a hinge.
scissor-extended-02 002.3dm (125.3 KB)
A constrain to an object only defines location but never orientation. So there is no need to make Object 23 hinging. On the contrary, making it a Hinge allows it to turn away from its parent (as I explained earlier). Since Object 23 is child (now firmly attached) of Object 30 the latter will take care of the necessary pivoting.
There are 50 ways to … solve a scissor-arm