Usually, when printing with PLA material the printed parts can change their size by 1-3% since this material has issues with shrinkage. MWO 3d printing models in our marketplace are modelled in such a way that all their parts are movable because of the joints. But in case of material shrinkage, friction of the joints may become insufficiently rigid, or vice versa, very loose.
First of all, we should note that the ball joint is not supposed to enter the claw/basket easily. Fitting one into the other should occur with an effort, then you’ll get a good hold. This is done to increase the duration of the frictional force of the joints and thus you can change the position of the model's parts more often without losing the necessary fixation of these positions.
Recommendation: connect the joints first to the claws/baskets with each other, and only then insert them into the necessary parts of the model. So, in case the joint will break, you will not suffer to get the broken detail from model part.
If the joints have such a tight fit that it causes the splitting of some parts then this problem can be solved in two different ways:
1. All parts of joints should be printed at 100% infill to withstand the pressure force during the insertion of the joint into the claw/basket, as well as when moving parts with rigid friction.
2. You can try to decrease the scale of ball joints at 1-3% in your slicing program. An example of how to do it in Cura - http://prntscr.com/jeu46t. If you print the ball joints 1-3% less you will able to easily insert them into the claw/baskets, while the ball joints itself will also enter the body of the model. The rigidity of friction can be reduced but this can be solved after painting.
Moreover, if the joints happen to be too loose, it may also help if you prime the model and paint it, or add a thin layer of any nail polish in places where joints are connected if you do not wish to paint the model. We have found out that after some time the material may undergo some more shrinkage, but this may be avoided if you prime/paint the element at once to block oxygen from leaving the printed element.