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enter image description hereI have two alum plates (45cm x 20cm x 1mm) that are hinged on the long side with two 30 x 80 hinges (30 x 40 each tang) in the middle, and "L" bracket / 20mm brace at the ends secured with a M4 loc nut and bolt. As you might imagine, however much you tighen the lock nut on the M4 mushroom bolt, it cannot keep the flap up due to the "mechanical advantage" of the plate weight. Or, if tighten to the nth degree to hold plate ... the latter cannot be repositioned!

I have looked at 'stays', but they will only 'lock' in the fully open state, (I need to hold the flap between -90 (closed) to +20 from horizontal)

My idea at present is to construct a stay using two flat alum bars constucted as a "V" with the outer points at around 4" on the unit and barn door, and the pivot at about 7" (ie pointing forwards) The pivot will have a fixed bolt / thumbwheel.

It's this latter part I seek advice on. Even though the surface area will be larger - and so I could use a M6 bolt - is there any action I can take to make the friction grip between the approx 1" diameter area on each bar stronger? (A fibre washer will reduce the contact area of metal, so that might not be an option)

In an ideal World, I'd opt for something like a plastic 'crown' gear fixed on each component. When loosened, you can turn the item to a new angle before re-engaging teeth again. (A system used on some cheap Chinese photo light fittings)

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  • $\begingroup$ A sketch would be appreciated. hard as I try, can't see what you have in mind. $\endgroup$
    – kamran
    Apr 12, 2019 at 19:25
  • $\begingroup$ Your last paragraph contains a solution but these have been made in metal as well... $\endgroup$
    – Solar Mike
    Apr 13, 2019 at 6:14
  • $\begingroup$ Solar Mike, you say these devices have been made in metal as well. Can you give a few pointers? $\endgroup$
    – Cristofayre
    Apr 13, 2019 at 17:47
  • $\begingroup$ kamran.As requested, have added a picture which may help explain the various concepts mentioned in text $\endgroup$
    – Cristofayre
    Apr 13, 2019 at 18:27
  • $\begingroup$ I admire you drawings and attention to detail. Good luck. $\endgroup$
    – kamran
    Apr 15, 2019 at 3:50

2 Answers 2

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As stated above, I went for 'parallelograms' As it happens,the wing nut clamping against a square M6 nut between bars has proven sufficient to hold the doors in any fixed positionThe bars holding the flap open

The bars in the closed position along case edge

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Caravans use friction stays to hold their windows open. You might be able to obtain them and use a couple to keep the barn doors open with slight modification.

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  • $\begingroup$ I looked into those, but they require a sliding channel down side of window, and only open about 80 degrees (if a 'limiter' is the same mechanism) $\endgroup$
    – Cristofayre
    Apr 22, 2019 at 17:50
  • $\begingroup$ I am going to create something called a "parallelogram" Basically, the 175mm upright stays level with the casing, whilst the 75mm shorter arm mimics the position of the barn door. Where the two meet will be a 20mm diameter area,so will place a rubber washer in that area. When closed, it will be 200mm long, (the arm pivot point is 175mm from top,and the short arm will swing in a downward radius) and thus shorter than the door itself $\endgroup$
    – Cristofayre
    Apr 22, 2019 at 17:55

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