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I've been unable to find a clear explanation of the design principle behind a ball bearing door hinge.

In the image below, the casing for a ball bearing assembly is highlighted.

enter image description here

One description states:

Ball bearings are engineered to throw the knuckle weight against specially hardened steel raceways, which ride on the bearing surfaces. The one-piece cup protects the bearings from moisture and dust.

Can anyone clarify what this means, and the internal layout of the assembly?

I'm also wondering about their durability, given that the mechanism isn't solid metal, but has internal (presumably moving) components under the casing. How thick is the casing, and does it carry all of the vertical load, or is the load shared with the internal components?

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    Note that any out-of-plumb conditions will be revealed with low-friction hinges. Doors that might've stayed put with conventional hinges will now wander to their lowest point. it only takes a very tiny lean in the jamb to cause this. For that reason, I tend to avoid them.
    – isherwood
    Commented Oct 9, 2019 at 13:22
  • Are you asking how a ball bearing works?
    – Harper - Reinstate Monica
    Commented Oct 9, 2019 at 16:55
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    I think the main point of confusion is that a typical "ball bearing" allows a shaft to rotate inside a hole, but in the case of these hinges, the balls are allowing a top plate and bottom plate to easily rotate (the balls support the weight of the door, not the rotation of a shaft).
    – JPhi1618
    Commented Oct 10, 2019 at 15:34
  • It's all ball bearing these days
    – LarsTech
    Commented Oct 11, 2019 at 13:53

2 Answers 2

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The casing is very thin and its purpose it to keep the bearing's balls in place, protect them from dust and grime and to hold in some lubricant. It doesn't share any load. The hinges are very durable as the friction load is much less than with a regular hinge. They are also quieter.

Below are a few diagrams on what might be inside a ball bearing hinge:

enter image description here

enter image description here

Hope this helps.

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    Congratulations on finding the diagram! Dramatically improves the quality of the answer.
    – Martin Bonner supports Monica
    Commented Oct 9, 2019 at 13:56
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The casing is just to stop the balls falling out. It doesn't take any of the vertical load. Inside the case there is a series of ball bearings arranged around the hinge pin. The ball bearings take all the load. When the hinge is turned, the balls rotate. The result is that there is no sliding of metal surfaces over each other, so there is very much less friction than with a normal hinge (where the two parts of the hinge just slide over each other). It is the same reduction in friction when you try to drag a bike with its wheels jammed, compared to when the wheels can turn.

They should be much more durable than normal hinges because of the reduced friction (leading to less wear). They can also take much heavier loads without sticking.

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  • Given that even solid core doors move fairly easily on normal pin hinges, I hate to think of what sort of door needs a ball bearing hinge, and what sort of attachment it has to have to the both the door and the frame.
    – Sherwood Botsford
    Commented Oct 9, 2019 at 12:59
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    @Sherwood - it's not just for people, but so that automatic door closers can use a lighter spring.
    – Robin Bennett
    Commented Oct 9, 2019 at 15:28
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    @ Sherwood Botsford Some of those plate glass doors are extremely heavy and have threaded holes for the hinges.
    – JACK
    Commented Oct 9, 2019 at 15:49
  • Great explanation. + I only posted an answer because I found the diagram.
    – JACK
    Commented Oct 9, 2019 at 15:53
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    Think of a heavy fire door, that needs an auto closer, but must also be easy for people to open. The ball bearing hinge allows an autocloser that is easier to push against.
    – Walker
    Commented Oct 9, 2019 at 16:11

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