Safe Hinge Theory

[djed]

I’ve been rethinking about how a safe hinge is supposed to work.

When a door swings open, is the weight of the door supposed to ride on the hinge pin - OR - is the weight supposed to ride on the hinge body with the hinge pin only being a guide to ensure the hinge upper and lower body stays aligned?

[MartinHewitt]

Yes.

I believe that it depends on the design of the hinge. With modern safes where the hinge pin is adjustable with a screw it rides on the hinge pin, but I do see also modern cheap safes, where the hinge is only the guide. I think there are a lot of designs out there.

More questions: Does the door ride only on the bottom? Only on the top? On all? I have a safe which has an adjustable hinge pin only on the bottom and I have one which has all three hinge pins adjustable.

PS: Is the hinge pin in the door or in the body, top or bottom? Adjustable hinge pins often have a securing grub screw. Some have bearing balls on top of the hinge pin. Very, very few have grease nipples to inject grease to the hinge pin. Proper maintenance guidelines for hinges without a grease nipple would be very interesting. I can find from manufacturers only instructions to put oil into the gap. Is this good procedure?

[demux]

I am not a physics major (though I took some in college), but I think the answer would be yes to both. There's the weight of the door itself (force of gravity) which is pulling the door down and being countered by the bottom of the hinge pushing up. However, at least with the door open, the center of gravity of the door is outside of the box of the doorway, which means there's also a moment that is trying to pull the top hinge away from the safe body and push the bottom hinge toward it. These are the forces that would be counteracted by the pins.

(It's been almost 20 years since I've been in college so anyone here that is a physics major will have to forgive me if I messed up some of the terminology, but I believe the basic concepts above are correct.)