Rivet the joints!

I have developed a process of creating the smallest hardware possible for the tiniest functioning joints conceivable, and it involves the use of some raw 3D printer filament from your spool, and your soldering iron.

For this step you will need some of your gray 1.75mm PLA filament. (I'm using a bright color for visibility)

Cut the raw filament into 7 - 8mm long pieces (you can eyeball this). You'll need (16) of these pieces. They will be your rivets:

Each (1) leg should have a hip bone and shin that is joined together by (2) tibias and (2) fibulas sandwiching the femur and shin on either side:

The set of tibias (shorter bones) should be above the fibulas (longer bones). The finished leg should match this orientation:

Thread your rivet through all of the holes, so that a small amount pokes out on either side of the bone:

Take your soldering iron, and carefully drag the edge of the tip at an angle along the portion of the rivet protruding from the hole in a slow circular motion until the end piece looks like a bead or round shape. Be careful not to make contact with the actual bone itself:

I found that the easiest way to do this is to connect all pieces to either the femur or shin first. The cap of your rivet should be as low profile as possible but still have a little meat to it:

After shaping your head cap on one side, you can flip the leg over and press it firmly against your bench. By doing this, it will force the rest of your rivets to poke out as far as they can on the side you're about to weld.

Repeat the step of melting the end of the filament pieces. If you did it correctly, the rivets will not be able to slide out in either direction, and will be mostly flush with the bone. Should look like this:

Notice that the rivets are tight enough that the leg bones can't fall straight down with gravity. There should be enough friction that they can stick straight outwards on thrown. This is important to achieve if you want your spawning to be posable!

Now attach the opposite ends of the tibia and fibula to the shin with the bare end pointing in the opposite direction as the bare end of the femur. The shin should fit snugly between the two sets of parallel bones:

Repeat the rivet welding process just the same as before:

Once finished, you should have a fully posable, spawnling leg like this! Isn't it fun to fold and unfold???