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Discussion Starter · #1 · (Edited)
HELP PLEASE: Tension/Torque/Torsion Hinges for Angled Sink Mirror

Our master bathroom has an angled mirror above the two sinks. The mirror is 12.5 inches tall, but spans the full width of the counter (66.5 inches). Above the angled mirror is a window, which explains why the builders could not install a full size flat mirror. The mirror is held at a fixed 19 degree angle by triangle wedges that the builder cut from a 2x4.

The problem is that my wife is short and has to stand on her toes to put on makeup, and I have to bend when I shave. We want a mirror with an adjustable angle.

I plan to replace this mirror with one that is mounted on friction hinges at the top of the mirror. This will allow us to adjust the angle of the mirror as needed, so the mirror will hold the new angle. I have yet to decide whether I need two or three friction hinges.

(Note: Friction hinges are also known as torque hinges or sometimes torsion hinges. What I need are hinges

HERE ARE MY QUESTIONS:

* Which hinges should I buy? Can you recommend a particular make and model of tension hinges for this application?

* What torque spec is the correct value so that the mirror will stay at any reasonable angle, but not be too stiff to move? (I assume that I will use two or three tension hinges at the top, to hold the mirror in place.)
 

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Discussion Starter · #2 · (Edited)
Addendum: I have done some math, which I will share here, but there are some many tension/torque/torsion hinges on the market, it is difficult to choose. Here is my math:

Mirror Dimensions: 12 5/8 x 66 1/2 inches

Weight estimates:
Weight of 3/4 inch plywood backing, at 2.3 lb/sq.ft. = 13.4 pounds
Weight of 1/4 inch mirror: 17.5 pounds
Weight of primer, mastic, mirror supports, etc. = 1 pound
Total weight = 32 pounds

Torque formula = Weight x CG distance x cos(angle)
(Because the weight is distributed evenly, the center of gravity in this case is 1/2 the 12 5/8 inches length, which is 6.3 inches.

TORQUE CALCULATIONS:

* 0 degrees (mirror held in place horizontally, like a shelf, which may not make sense for this application, but is the MAXIMUM torque necessary):
32 pounds x 6.3 inches x cos(0 degrees) = ANSWER: 211 inch pounds of torque
Two hinges = 105.5 inch pounds each. Three hinges = 70 inch pounds each.

* 71 degrees (current mirror angle):
90 - 19 degrees mirror angle = 71 degrees.
32 pounds x 6.3 inches x cos(70 degrees) = ANSWER: 69 inch pounds of torque.
Two hinges = 34.5 inch pounds each. Three hinges = 23 inch pounds each.

That's a lot of difference between the two measurements (211 vs. 69 inch pounds). I want hinges that will definitely hold, but they can't be so stiff that the mirror angle is difficult to adjust. I could use some help choosing the correct torque spec makes sense.

I would appreciate any advice or experience that you can share, regarding which brands and models of tension hinges to consider, as well as the proper torque spec necessary for the angled mirror adjustments.
 

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Call me a skeptic, but I don't think you will be pleased with your plan for an adjustable mirror. You will be trying to hold and adjust the angle on a mirror over 5' in length.
I would remove the existing mirror and use the side panels to install a hinged mirror on each side. (2)
I think you will more pleased.
 
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