okay so ive seen them around a lot, and i know there are lots of differnt types butbut i dont understand them very well, and i was wondering if someone could answer these questions n_n what purpose do they serve? are they nessasery? (i think they have something to do with double joints?) how would you go about making them? thankyou in advance for any advance n_n
Locks keep a joint from moving unless you want it to, giving it a much more solid grip than a normal ball or hinge type joint would. For example, you might want a hip joint to lock for a good, solid standing position, and also lock when the doll is sitting, or you might have a lock in the elbow to keep the elbow straight, and another for it fully bent. They may or may not be necessary. Factors that may affect its necessity would include things like the amount of friction (which can be increased by the amount of surface area of the joint and cup in contact with each other, or changing the texture of the joint by making it not so smooth in casting, or by sueding or hot glueing), the weight of the parts, the size of the doll, and the design of the joints. Locks usually consist of two parts - a groove, dip, or other "negative" space, and a matching notch, bump, or other "positive" part. You can carve away a small groove inside the cup part of a joint, and then add a matching bump to fit into that groove. I've also seen very advanced "locks" that one side looks sort of like a golf ball, with lots of little divots all over, and the other side has a set of matching bumps, so the entire surface of both the cup and ball become locks. I haven't been able to be hands-on with that kind of joint though. You can also have a lock that has no corresponding "negative" exactly - a little set of "teeth" on the back of a double jointed knee, which hook onto the back of the upper thigh, to keep the knee joint from moving when the leg is straight, for example (my ResinSoul doll has a locking knee sort of like this). Purely my opinion: I think locks should be used sparingly, because they are difficult to design well, and doing them not just so means that they actually make the joint work less well except when locking... The "positive" part raises up the ball off the surface of the cup, resulting in less friction, and also changes an otherwise round and smoothly moving joint into a slight ellipse. The result of this is that in certain parts of the rotation, the elastic is shorter than in other positions, so the joint will want to snap back to its shortest path, making the joint "kicky." How big an issue this is, of course, depends on how the joint is designed, and a joint can be kicky without a lock on it, but... it doesn't help.
