Cy/Cool Girls are made from high quality materials, but unfortunately removing and refitting the feet or ankles could put a lot of strain on the knee joints, so much in fact that the knee joint can break.
When a knee joint breaks you will probably be shocked and sad, but don't worry, it can be repaired.
The procedure to repair a v1 knee differs slightly from that for a v2 knee.
steel (not brass) threaded rod (DIN M2 in Europe, in any case about 2mm/0.0787in outer diameter)
steel cloth pin (about 0.7mm in diameter)
Using the pin vise and the 0.7mm drill bit, drill a hole in the inner seam of the leg 7mm (0.276in) from the lower edge of the thigh. Keep the drill at a right angle to the leg and aim straight for the center of the leg (i.e. the drill should point to the seam on the other side of the leg).
Drill about 7mm (0.276in) deep, you can feel the resistance lessen when the hole gets about 1.5mm (0.059in) deep then it will increase again when the hole gets about 6mm (0.236in) deep.
The increased resistance means that you are drilling into the axial hinge rod (which is what we want).
Cut the pointy tip of the cloth pin and chamfer the tip with the file, removing any sharp edges. Insert the pin into the hole in the side of the thigh, this will lock the axial hinge pin, allowing you to drill a hole and screw the threaded rod into the hole in the pin.
Put the 1.5mm drill bit in the pin vise and gently drill a hole through the center of the axial hinge rod in the thigh, make the hole about 6mm (0.236in) deep.
Drill a hole through the center of the small disc located on top of the knee hinge disc on the lower leg, aim for the center of the knee hinge disc and drill about 4mm (0.157in) deep.
The pictures show the knee joint with a piece of threaded rod already screwed in.
Cut a 10mm (0.394in) length of threaded rod and cut a groove in one end (using the thin file or the miniature grinding disc). Make the groove fit the blade of the small screwdriver. Use the screwdriver to screw the threaded rod into the knee hinge in the lower leg.
If you have a wire cutter you could use a screw instead of a length of threaded rod.
If you use a screw, put a nut on it before screwing it into the knee joint in the lower leg, once the screw is all the way in the knee joint, turn the nut away from the head and cut the head off.
Use a file or mini grinder to clean up the thread at the cut and then turn the nut off. That way the nut will restore any minor damage to the thread.
Each method has its benefits and drawbacks:
Using threaded rod it is fiddly to get the rod screwed in (depends on how accurate you can cut the groove for the screwdriver) but wear and load on the knee joint is minimal;
Using a screw it is easier to screw it into the knee joint, but cutting the head off and restoring the thread will put quite some force on the knee joint, which may result in the joint getting looser or the screw becoming loose in the joint.
Now take the lower leg, straighten the knee joint and gently screw the threaded rod into the hole in the locked pin in the thigh. Continue screwing until the leg has the same length as the other leg or until the knee joint bits are tightly together, then remove the cloth pin and check if the joint rotates and bends.
If you work carefully, the result will be at least as strong as the original knee joint was.
Save the cloth pin in case the threaded rod comes loose later.
If the threaded rod comes loose, screw it out of the joint (insert the pin to lock the axial hinge first), put some super glue on a long cloth pin and apply the glue to the deepest part of the hole in the joint, then screw the threaded rod back in.
Instead of super glue you could also use Liquid Thread Lock if it doesn't harm the plastic of the knee joint (some brands are safe on plastics, some aren't so better check and test first).
repairing a CG v2 knee
Sofar I haven't seen a genuine v2 body with a broken knee, but there are several lookalike bodies available that appear to be made of more brittle materials.
(Cloned) CG v2 body with broken knee.
Notice that the peg is way forward of the center of the knee hinge, this makes the rear of the knee hit the cover on the thigh when trying to rotate it, so we can not simply insert a piece of threaded rod and screw the parts back together again.
The good news is that the broken peg inside the thigh can only be rotated by some 30 degrees, so this time we do not need to drill a locking hole into the side of the leg.
Fit the 1.5mm drill bit in the pin vise, apply a strip of masking tape at about 6mm (0.236in) from the tip and gently drill a hole through the center of the axial hinge rod in the thigh, make the hole about 6mm (0.236in) deep.
Still using the 1.5mm drill bit, drill a hole through the remains of the knee peg (or the center of the small disc located on top of the knee hinge disc) on the lower leg, make sure to drill perpendicular to the peg and drill about 4mm (0.157in) deep.
Then use the 1.9mm drill bit to widen the hole. In case the diameter of the threaded rod is not 2mm, then use a drill size slightly smaller (about 0.1mm, 0.004in) than the diameter of the rod.
Cut a 10mm (0.394in) length of threaded rod and cut a groove in one end (using the thin file or the miniature grinding disc).
Make the groove fit the blade of the small screwdriver.
Use the file or mini grinder to clean up and chamfer the edges of the rod, then run a nut from one end to the other to restore any minor damage to the thread.
Remove the nut again.
Use the screwdriver to screw the threaded rod into the knee peg in the thigh, leave a length of 4mm sticking out.
Screwing in the rod has rotated the peg clockwise, so rotate it back until it is about in a centered position. This helps the surfaces of the broken edges of the peg to line up properly in the next step.
Now take the lower leg and straighten the knee joint.
Use the clothpin to apply a couple of drops of CA to the inside of the drilled hole.
Apply another drop of CA to the threaded rod sticking out from the thigh and insert the rod into the hole in the knee joint, this should require some force as the rod should fit very snugly.
Make sure you don't spill any CA on the knee joint, gently rotate the axial joint and bend and stretch the knee to make sure the joints move freely.
Let the CA cure for a while and check if the joint rotates and bends.
If you work carefully, the result will be at least as strong as the original knee joint was.
Firming up floppy knee joints
Some of the CG v2 type B bodies come with rather floppy knees that may cause the figure to fall over.
To make the knee joints firmer, apply some cyanoacrylate (a.k.a. super glue) to the seams of the joints.
To apply the CA glue accurately, apply a drop of CA to the tip of a cloth pin, then touch the seam with the tip of the pin.
After the CA is applied to the joint it will creep into the joint, be sure to move the knee joint repeatedly until the glue has cured (this may take up to 15 minutes), else the knee becomes permanently stiff.
