Cy Girl - CG v2 Style Hip Joint Repair

This page shows how a CG v2 style hip joint is assembled and how to repair a broken joint.

The best way of repairing a hip joint broken like this one was, is actually to cut the hip section apart, take the broken part out and repair and reinforce the broken part.
However as the hip section holds both the hip joints and the spring-loaded pelvic joint, I'd prefer not to open it unless I really need to.
So I came up with a less complicated repair which is described below.


Disassembling the broken hip joint

The CG v2 hip joint is a clever complex joint allowing movement along 3 axis (forward, sideways, axial rotation), resulting in a range of movement similar to a human hip joint.
ZC Eve bodies come with a type of hip joint that is virtually identical to the CG v2 hip joint. The body shown here is a ZC Girl/Walking Paradise body with a partially broken hip joint.
I tried to repair this so I took some pictures disassembling the broken joint.

imageThe hip joint consists of a disc sandwiched between two semi-spheres, the spheres end in a pivot that is mounted in the pelvic section, the disc ends in a pin that is mounted in the thigh.
Each of the semi-spheres provides half of the pivot pin that is fitted to the pelvic section. In this case the pivot pin from the right front semi-sphere is broken.
imageIn the rear semi-sphere a small screw is fitted, I started dis-assembly by removing this screw using a size 1 '+'-blade screwdriver.

Note that it makes no sense removing the screw if the hip pivot pins are still intact as this will only loosen the joint, the joint will not come apart.
The screw only serves to add friction to the sideways movement of the leg.
imageIf not broken, the semi-sphere in which the screw is mounted could be lifted off by bending it (Note that this will probably cause it to break near the hip joint !), but the semi-sphere on the other side has a hollow hinge pin that runs all the way through the joint and there is no room to lift the leg off that pin.

Here it becomes clear that the broken part can not be repaired without cutting the pelvic section open or modifying some parts of the joint: the sphere-shaped part of the hip joint can only be assembled before the pivot is inserted into the pelvic section, there is no way to fit the disc of the leg between the semi-spheres (actually: replacing the fixed hinge pin by a removable one could do the trick but this requires a second screw which will end up in plain sight and might make the joint less stable. Replacing one defect by another one is not a successful repair IMHO).

(Using a nut-and-bolt might work though: cut the hollow pin off along the edge of the semi-sphere, firmly attach a nut inside the semi-sphere, cut the hollow pin to the exact width of the disc and replace the screw by a bolt. Enlarge the hole in the hollow pin so that the bolt will rotate freely (otherwise it will be impossible to screw the bolt through the pin) then insert the hollow pin into the disc. Now the disc can be slipped in and out of the two semi-spheres, so the broken semi-sphere could now be repaired.)
imageBroken part removed, showing the hinge pin that runs straight through the joint.
Note that to remove this part the disc on top of the leg needed to be rotated by half a turn.
imageBroken part reassembled, this is what the joint would look like after the broken part is repaired.
Note that the disc in the leg can not be inserted into the joint because of the hinge pin.

To repair a hip joint that is completely or partly broken off the body, the hinge pin between the semi-spheres needs to be made removable.
Assembling the joint means that the semi-spheres have to be rotated several times before the pin is inserted and fastened, it is likely that the repair will break again when the semi-spheres are being rotated.

Repair

To repair the broken part I decided to fit a piece of steel wire to keep the broken parts aligned, then use some gel-type CA glue to join the broken parts and hope for the best.
Tools and materials required for this repair:

imageUsing a pin vise, drill a 1.5mm hole about 4mm deep into the center of the broken semi-circular pivot.
Mark the edges of the hole with a fine tipped water-based fiber tip pen, then fit the broken semi-sphere in its place and remove again. This should leave a circular mark on the outside of the tab on the semi-sphere indicating where to drill.
Drill a 2.0mm hole at the marked location on the tab on the semi-sphere.
The picture shows both holes.
imageUse a fine file, fine saw or cutting disc (in case of cutting disc: wear safety goggles !) to cut a slot in one edge of the threaded steel wire, then cut a 5mm length of wire and run some nuts along the piece of wire to restore the thread at the cut.
Use a flat bladed screwdriver to screw the wire into the hole in the hip, leaving the tip of the wire protrude just below the level of the unbroken half.
Use the fine file to remove any sharp edges.
imageClose up view of threaded wire in place. The hole in the tab of the semi-sphere is just large enough to fit tightly over the protruding bit of wire.
imageTo assemble the hip joint, rotate the disc on top of the leg as show (the disc is symmetrical so either side of the disc can be on top).
Then push the hinge pin of the semi-sphere into the hole in the disc, it will take some effort to get the edge of the semi-sphere past the edge of the leg.
imageAfter the semi-sphere is snug against the disc, rotate the disc and the sphere axially, then rotate the semi-sphere until the tab fits the recess in the front of the leg.
imageUse cloth pin to apply small amounts of gel-type CA glue at the locations marked in violet. Make sure the glue can not spill into the pivot.
imageFit the leg to the joint, making sure the hole in the tab of the semi-sphere fits over the wire and the hinge pin fits into its recess in the semi-sphere.
imageAfter verifying that the hole for the screw lines up with the hole in the hinge pin, leave the leg for a minute or so to allow the CA glue to set, then carefully move and rotate the hip joint to make sure the glue has not fused any of the pivots.
imageFinally after the glue has set and movement of all parts of the hip joint are verified, fit the screw using the size 1 '+'-bladed screwdriver, tighten the screw just enough to have the leg hold any spread positions. Do not tighten the screw too much as this puts extra strain on the hip joint when the leg is moved sideways.




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