The turret bearing
The Tiger I had a fully rotating turret carried on a ball-bearing race.
This diagram, extracted from a manual [3, see plate 65] , represents the first version of the device. Ball bearings are trapped in a "race" between two concentric steel rings. The overall diameter ("Außendurchmesser") is 2100mm [3, see page 9] in all versions.
The original design
The original design of the device had 158 ball-bearings, their centers lying on a circle of 1990mm diameter. Every second ball was load-bearing [1] with diameter 40mm. Between them were "spacer" balls of diameter 39mm. The ball race was "crowded", with very little space between balls, as this model demonstrates.
The steel rings have been sectioned in this model. The inner one has a complex shape because it also carries a sealing mechanism for submersion, which is not shown here. We can see bolt holes in the top surface of the outer ring. The inner ring has bolt holes in its bottom surface.
This is the complete bearing seen from below. The inner ring has 24 bolt positions for attachment to the hull, with apparently no "front" direction. Interspersed among them are 8 positions for screws that attach a "toothed ring" under the bearing ring.
This view from above shows that the outer ring also has 24 bolt positions where the turret's "support ring" can be attached. But we can see two additional details: both rings have a small notch.
These two "filling notches", when brought together, form a "filling hole" through which ball bearings can be inserted into the space between the rings. I don't know if these notches were supposed to be put at a specific place when the device was attached to the vehicle, but it's safe to assume that the notches should not align until the turret is turned to an unusual angle.
The outer ring's notch was located 45 degrees to the right (1:30 o'clock). I don't know if the inner ring's notch had a mandated position. I have modelled it as found in the Saumur Tiger during restoration, but that turret may have been attached wrongly. [3, see page 9]
A "new" turret was introduced on Tiger 250391 in July 1943 [2, see page 81] . It introduced many changes, including a redesign of the ball bearing race. There were now 113 load-bearing balls, each one carrying a loose ring of 55mm diameter [3, see page 9] . Trapped in the vertical alignment by the ball races, these rings kept the balls evenly spaced. Also, the balls were moved slightly outwards, so that they now lay on a circle of diameter 1995mm.
Although we have not found documentation about it, there was apparently a third and final arrangement of ball bearings. The preserved Tiger at Saumur Museum has it. In this case, there is a ring on every second ball. The number of load-bearing balls is now 130.
Bearing race rings
This model shows the assembled ball bearing race. It's the final version, which is the simplest version.
This is a cutaway of the mechanism. The spacer rings fit loosely in the gap between the bearing rings.
in the outer ring, as this image shows, there were some gaps in the sequence of bolt holes. Equipment in the turret made it impossible to use those positions. The upper ring therefore attached to the turret in only one orientation.
