I think welding works fine, I weld parts to my rigs all the time and I never face any issues. The only thing you need to remember is to always weld the parts to the moving part itself, meaning you can’t weld, for example, a “blade” part to the “handle” part, and then the “handle” part to the “hand” body part, the handle will move fine but the blade part will not move, I’m sure this isn’t related to your issue but you can use it as future reference I guess.
There could be several issues here but it’s hard to pinpoint what it is with very limited information. For example, you might have welded the tool in the order of “Hand --> Tool”, where instead it should be “Tool --> Hand”, basically the tool needs to be the parent of the actual weld. Since the hand is the one moving, you can’t weld the hand to anything, because you are essentially “locking” it to the part you’re welding it to, which means that the part that the hand is “locked” to is the part that will ultimately end up moving the hand (if it were to be movable).
Any other issue that i can think of should be detectable by Den_S’s warning prompts in his plugin, like naming issues or decals and such.
That’s all I can help you with, good luck!