Here's a way to repair a broken CG v1 or v2 knee joint.
Tools and materials needed:
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 wire 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 wire already screwed in.
Cut a 10mm (0.394in) length of threaded wire 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 wire 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 wire.
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:
Now take the lower leg, straighten the knee joint and gently screw the threaded wire 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 wire comes loose later.
If the threaded wire 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 wire 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).
Cheers,
-- Eric.
Tools and materials needed:
- Pin vise
- 1.5mm (0.059in) and 0.7mm (0.0276in) drill bits
- small screwdriver
- wire cutter or screw cutter
- thin file or motor tool with miniature grinding disc
- threaded steel (not brass) wire (DIN M2 in Europe, in any case about 2mm/0.0787in outer diameter)
- steel cloth pin (about 0.7mm in diameter)
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 wire 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 wire already screwed in.
Cut a 10mm (0.394in) length of threaded wire 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 wire 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 wire.
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 wire it is fiddly to get the wire 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 wire 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 wire comes loose later.
If the threaded wire 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 wire 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).
Cheers,
-- Eric.
