four bar linkage: design?

[VJ]

Hello,

A friend want to make a piece of furniture, which includes a board that can move. The board has the estimated size 160 cm x 10 cm x 2 cm (horizontal length x height x depth); the movement should be:
horizontal position: 50 cm from the floor, 20 cm from a reference point on the right
vertical position: 20-30 cm from the floor, 0 cm from the reference point
This clearly cannot be achieved with a regular hinge. But I googled a bit and think it is possible with a fourbar linkage, to make the board move on 2 hinge points.

How do you start designing that? Is there freely available software to help with this?

(if it is too difficult, he may have to go with a simpler solution, but he first wants to give this a shot)


Jörg

[Greebe]

Would help to know the function of this sling board. Side to side movement? No forward or back or the other way around? Does it hang suspended or supported from underneath?

Scratch something on a napkin would ya

[VJ]

I finally managed some time to draw it. idea.png

The black rectangle is the one that should move, from the horizontal to the vertical position. It should not have any other movement (ideally, a 90° rotation along its length axis would be interesting, but this would complicate it a lot. The attachment points would have to be inside the red rectangle; no part of the mechanism should be visible above the bar (when in horizontal position). For stability, it will probably have some fold out leg, but that is not the issue.
Ideally, we would like to make it with standard furniture components (e.g. those hinges used on bar doors or those extending ones used for cabinet doors that move upward - not sure what they are called). Main problem is how to design the links that allow for this movement (not even sure it is possible)

[Greebe]

What architectural limitations are there to this design. I see solutions, but they may not look appealing cosmetically.

edit: Oops, forgot to shorten the length in the horizontal position, but you should get the idea

[Greebe]

Cut the lower black/green (white/green expanded view) hinge pin at a 45° diagonal with the flat perpendicular to 225° and the arc pointing to 45°. The lower slot is the width of the dowel pin measured from the points indicated. This hinge pin will entrap the shelf so that it resists going lower than 90° or upright beyond 0°, yet becomes loose when lifted up. There are many ways this can be changed, double compound hinges, mounting from below. But structurally speaking this is the most common method used.


edit: That'll be $50

[VJ]

Thanks! Interesting idea!
I was too much focussed on needing some double hinge system.

However, is there a solution with nothing sticking out above the bar when it is in horizontal position, and nothing to the left of it (the side where it folds out to) when it is in vertical position? Things sticking out below (but not hitting the ground), or to the right are ok.

[Greebe]

Thanks! Interesting idea!
I was too much focussed on needing some double hinge system.

However, is there a solution with nothing sticking out above the bar when it is in horizontal position, and nothing to the left of it (the side where it folds out to) when it is in vertical position? Things sticking out below (but not hitting the ground), or to the right are ok.

It was drawn to show detail, not that the support bar is external. Functionally speaking it could not work external or would bind up when folded. Visualize man Visualize

A double bracing hinge can be used below, but have the nasty habit of guillotined fingers and why they are not used. Have to think that one up, it's not on the ready list in that card file in me head atm


....
Formulating thoughts... would a gas piston linkage work for your purposes? it would replace a cheaper but clanky mechanical spring. Tho spring could possibly be inlaid into the edge with a bullnose router bit. Hmmm still thinking...

[Greebe]

The cross support could be removed and the stop bloc changed. Shelf/hinge pins would need to support total weight and balance so as to not tip forward when extended. Dowel pins and routed notches used to lock the piece into place be it in the horizontal or vertical position.

[VJ]

When I saw your drawing, I also started thinking about a gas piston (e.g. instead of the blue bar you drew).

Still, not sure how to hide it... from the current view, the black bar should end up behind the red one. But the mechansim should not be on the front of the black bar I drew, but it should be behind the red one.

[Greebe]

I see the black bar as a shelf and the red end as one of two panels on the ends supporting the shelf. The blue brace is between the black shelf and the red end. This is normally some thin metal stamped out, but can also be made of (ply) wood. If the blue brace is removed the block can be altered into an upside down L eg ¬ and would function the same. Strength of the shelf must be enough to handle the total weight at the fulcrum. The red end caps must supply support so it doesn't fall forward when, 1. shelf is laid flat, 2. objects placed upon do not cause it to tip forward or 3. hands or arm weight doesn't cause the same issue.

[VJ]

Well, it is not really a shelf, but yes, something like that.

My drawing showed the front view, with the black bar hiding behind the red one (not in front of it). We'll have to rethink some things, because it looks like there may be too much clearance (for support, a leg could be added to the black bar, so that is no problem, but but it may not be very sturdy regardless)... But you have great input, and opened up some new ways for us to consider the problem (we were stuck with a four-bar linkage mechanism). Thanks!

[VJ]

Your drawing gave me this idea:
idea.png
The blue is fixed to the black.
The green are two linkages that hinge on both sides (I've only shown them for the horizontal position, but they should fit for the vertical one as well).
I think it would result in the correct movement of the black bar, but it might not be stable in the horizontal position. I suspect an additional support would be needed. Perhaps a gas piston somewhere might also help for that... Vertically, I would assume gravity would hold it in place well enough.

Edit: just figured out that it would not work... back to the drawing board.

[VJ]

I may actually also put a hinge in the black bar somewhere near the middle...
If the bar than is a bit longer, and covers the red square, it could use a pivot point.
Something like --- to /\ to || (or even '|, it does not have to be in the middle)
(although this might be a less elegant solution)

[VJ]

Had another idea... what if the black bar would move differently:
idea2.png
(I haven't checked the lenghts if it makes sense, but just the concept)

Of course, it would still need something to hold it in place (gas piston or mechanic lock), but it may be simpler this way...