DIY Doctor

Locking Mechanism Help and Suggestions for Folding Wood Board

Postby Nac2311 » Tue Apr 24, 2018 5:00 pm

Hi,
I hope I have the right forum.
I have a 2 x 4 board project that i'm working on (images open and closed below). Think of a paste table without the legs. The prototype in the image is basic wood and mdf, but the final version will be birch plywood base and rim. The two halves are held together by 2 hinges.

My question is what sort of locking mechanism could I use to hold it open.

When it's open against the hinge, it's fine - it's when you have it flat side up, the weight wants to fold it closed. I've tried using some wood and dowels, but its too heavy to support itself. I'm now trying to find something more rigid that will hold it open.

Does anyone have any suggestions?
Many thanks
Attachments
board-2.jpg
board-1.jpg
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Postby Sometimewoodworker » Wed May 02, 2018 8:04 am

Sorry to say that there is no easy way to do what you want.

Why do you need to use it with the hinges up? There may be a way to work around your desire to have the hinges on top.
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Postby Nac2311 » Wed May 02, 2018 1:19 pm

Hi there,
Thanks for your response sometimewoodworker.

I've been looking around and think I might have a possible solution - although I've not bought them yet - so I might be to soon with that comment.

Ratchet hinges (something like this:https://www.aliexpress.com/item/1Pair-2-PCS-LOT-Furniture-Adjustable-Angle-Adjuster-Mechanism-Hinge-Hardware-Sofa-Bed-Bedding/32687007808.html). If I put a ratchet hinge on either side of the frame, i'm hoping it will keep it open.

From a wood working point of view - what suggestions of fixing is best? What screws if i'm going into birch plywood and realistically - do you think it'll work? Am I overthinking the solution?

Many thanks again
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Postby Sometimewoodworker » Thu May 03, 2018 6:03 am

Nac2311 wrote:Hi there,
Thanks for your response sometimewoodworker.

I've been looking around and think I might have a possible solution - although I've not bought them yet - so I might be to soon with that comment.

Ratchet hinges (something like this:https://www.aliexpress.com/item/1Pair-2-PCS-LOT-Furniture-Adjustable-Angle-Adjuster-Mechanism-Hinge-Hardware-Sofa-Bed-Bedding/32687007808.html). If I put a ratchet hinge on either side of the frame, i'm hoping it will keep it open.



Your original question suggested that you wanted it to open 180 degrees with the hinges on top and to hold like that with weight on it

It very much depends on exactly how you want to us it. You haven't explained yet, so I can only guess without mor information.

The way those hinges are designed is that you have 80% of the weight on one part (the horizontal bed) and up to 20% on the other part.

It is not clear the exact range of movement but could be 90 degrees with 7 locking positions. Starting at 180 then 165 included are 120, 105.

You really need to see the range of movement. They will be available from a UK supplier

Nac2311 wrote:
From a wood working point of view - what suggestions of fixing is best? What screws if i'm going into birch plywood and realistically - do you think it'll work? Am I overthinking the solution?

Many thanks again


Are you overthinking? I have no idea because I don't know the usage.

As to fixing;

First, fixing screws into the edges of plywood and expecting them to hold against a shear force of any significance will not work, the plies will be forced apart. Fixing into the face is the only way you're going to have resistance against shear forces, guessing something like 10 or more times the resistance. Also with plywood you get the quality you pay for there are no bargains, the cheaper the plywood the weaker the glue bonds will be.

Second, those hinges will need to be roughly centred on the material you fix to they are 29mm wide so you need material with an absolute minimum of 40mm with a tough hardwood and probably I would not use them in much less than 50mm in a brittle hardwood or softer wood.

Third, the screws you will need should probably be no.12 or no.14 that is 5mm, 5.5mm or possibly 6mm the length will be dependent on the load, minimum 35mm probably longer


All of this is guess work as I've no idea of the loads involved or what you want to do .

Your question is a bit like saying "I've got some string, will it be long enough and strong enough?
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Postby Nac2311 » Thu May 03, 2018 10:59 am

Thank you sometimewoodworker. Apologies about being vague - got so much rattling around in my head that I didn't realise I hadn't said what i'm trying to do. The board is a 2 x 4 game board. The idea is that I can glue a vinyl sheet (which will have pictures and things on it) onto the smooth side so, when opened flat, you can play board games, the other side has a 60mm high rim which will have 3d terrain in it for miniature wargaming. The terrain is fiberglass so not too heavy. In gaming, on of the main problems is having the proper space to play the game. If you have a 2x2 kitchen table, but need a 2 x 4 space, then you simply open up the game board i'm making and lay it over the smaller table. It's fine when you have it terrain side up and the hinges are on that side (I can't put them on the flat side as that'd cause problems when laying out a board game). When you flip t the other way round on a smaller surface, it naturally wants to close - making that side unusable.
I'm thinking of making some buffer bars to push onto the side which might be a good locking mechanism in its own right, but if I didn't do that, how could I open this board and have it lock into position.
Really sorry for not saying this to start with, but many thanks for your help :)
Attachments
board-4.jpg
And the full size prototype from the inside (the frame height is wrong on this one - it will be 2x as high in the next version)
20171011_180119.jpg
and the inside
20171011_180043.jpg
This is a small visual prototype I made
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Postby Sometimewoodworker » Fri May 04, 2018 5:35 am

Okay it's now much clearer exactly what you're trying to do. The first point is that I wouldn't use those small hinges, I would use a length of piano hinge. The reason is that piano hinge is very much stronger even though the screws that you need to use to hold it will be much smaller.

The second point is that nothing that I know of will do the job you want, but having said the making a custom designed fitting is not rocket science it's really quite simple. You want something a little like the simple door bolt you have already fitted except with a much longer bolt.

You can modify the existing bolt holder by cutting it into about 3 sections (giving a total of 4) and drilling screw holes into each of the new sections (taking the bolt out first). You then attach them, one the hinge end of each of the boards (almost exactly as it is now) and then the other two about 20 cm away from those (longer is better but you will be limited by the handle you have fitted. You then buy a 50cm length of round silver steel the same diameter as the original bolt. This will lock the boards open when it's slid into the 4 guides

Repeat this on the other side for security. You should be able to work out how to make something to stop the bar sliding out.
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