fallow your code, i build a robot int threejs. But when i change the Joint2 angles, the axis just don't move around the own axis，it seems like the axis was around the (0,0,0). I checked my code and it just like yours, is there any problem about my *.stl files?
Best wishes,

1 the ScrittaKuka can not added to the fourth, because the fourth is not loaded yet.
So I chaged the code:
loader.load('KR5_850/Fourth.stl', function (geometry) {
var material = new THREE.MeshPhongMaterial({ color: 0x404040, specular: 0x111111, shininess: 60,map: text});
fourth = new THREE.Mesh( geometry, material);
fourth.position.set(-75, 0, -335-360-90);
//fourth.castShadow = true;
//fourth.receiveShadow = true;

				rt_block.add(fourth);
				
				
				loader.load('KR5_850/ScrittaKuka.stl', function (geometry) {
					var material = new THREE.MeshPhongMaterial({ color: 0xcc0000, specular: 0x111111, shininess: 60,map: text});
					var scritta = new THREE.Mesh( geometry, material);
					//scritta.castShadow = true;
					//scritta.receiveShadow = true;

					fourth.add(scritta);
				});
			
			});

2 can not render