Info on novel use of drawer slides requested

[Chris Knight]

I want to make a dressing table with a mirror that rises out of the cabinet - similar to say a flat screen TV, so that in the closed position, the top of the dressing table is flush.

I'd use a TV lift if I had enough height in the cabinet but unfortunately, I don't (the motor etc adds considerably to the amount of movement these lifts create) I have a 70 cm height in the dressing table and I need a 60 cm extension.

I have an idea for doing it by mounting the mirror on frame carried on full extension drawer slides and am looking for advice on a high quality, robust drawer slide suitable for this purpose.

I think the drawer slides will have to be used behind the mirror and obviously, they will be used vertically rather than in the normal horizontal position - I had thought of using rails with linear bearings but you can't get these as full extension devices and the cost is very high.

Perhaps folk who use these drawer slides can tell me how flexible/strong a couple or even three are likely to be when used in the way? The mirror itself is not too heavy - probably 15 pounds at max.

 

[MikeG.]

I think the sliding should work fine............but how are you hoping to stop the mirror crashing straight back down where it came from?

Mike

 

[Scott]

...but how are you hoping to stop the mirror crashing straight back down where it came from?

Like a sash window! Pulleys and big iron weights!

 

[wizer]

Accuride is the name to look for if you want top quality drawer slides. These are the ones used on server racks, etc. Tho, they are very expensive. I think three of the normal screwfix type will be fine for this application.

http://shop.comdir.co.uk/Products.aspx?intGroupID=999

 

[9fingers]

If you load the runners with ROCOL Kilopoise high viscosity grease and make the balance weights just heavier than the mirror, It should rise gracefully up when needed and a simple latch arrangement should hold it down.

With further cunning, arranging to release the latch when only two drawers were simultaneously opened would make it a 'secret' mechanism
Lots of opportunity for intrigue here!!


Bob

 

[CWatters]

How about having it pivot about the bottom corner of the mirror? Crude sketchup..

Would need a spring/motor to raise it. Possible a model boat sail winch would do it.

 

[p111dom]

I think full extension sliders will be fine but to make the action work and lock in place I'd use a car electric window arm and motor. Something off a small, old car like a Vauxhall Nova. The motor and arm are easily less than 70mm deep and all the parts you would need would be on the car. They also stay where they stop so in this case it would stop the thing falling down when raised. Would just require a 12V supply. The basic old motors only have three terminals. Two lives for either direction and one negative. From a scrap yard they are around £15. Not a lot for something that's going to look pretty trick when finished.

 

[big soft moose]

or a few gas struts off old motors (like those used on the boot opening) positioned under the mirror when it is on a couple of runners - this would mean that its default position would be up - but you could push it down and latch it.

 

[9fingers]

Gas struts I've played with are far too strong for this application.
They can support a whole tailgate with the effort usually applied only a few inches from the hinge axis ie a large magnification of the tailgate weight.

Bob

 

[Chris Knight]

Thanks for the suggestions everyone.

My present idea as Scott correctly divined is to use counterweights something like the sketch below

The rectangular thing is simply a "placeholder" for a frame that will carry a three piece mirror (one central section with two folding side sections). The idea would be to slightly overweight it so that it has to be pushed down gently to latch it. Bob's idea of a secret latch is a nice idea - might try to include something like that..

I think finding gas struts of the right spring rate would be a problem plus as I mentioned, I have very little room to work in - the closed length of anything cannot be greater than 70 cm and I need 60 cm extension - hence the twin pulleys at each side. The pulleys themselves would be quite small - probably 2cm diameter max with steel wires for lifting the mirror.

The drawer slides will thus have to constrain movement in two dimensions - forward and backward and side to side. Whilst there won't be any force on the mirror once adjusted, I don't want the thing to wobble around too much.

If need be, I think I can arrange three or four slides - two to constrain movement in one direction and the other one (or two) to act at right angles, constraining movement in the other direction. My preference however would be to use a single very meaty slide at the back of the mirror support frame.

 

[wizer]

I really like the idea, can't wait to see it

 

[Shrubby]

Accuride would be substantial enough - look up the specs at Hafele's web site. I bought some from Poole & Waite as they had the size in stock.
Something to hold the folding mirrors in place for retracting might be good. As simple as a sprung ball catch or rare earth magnet under each frame
Matt

 

[Chris Knight]

Tom,
It might be a while!

Shrubby, thanks - it looks as if accuride are the things from people's comments. I do indeed plan a magnetic latch to hold the side mirrors in place when lowering the assembly.

 

[wizer]

Tom,
It might be a while!

Heheh I know how that goes

 

[Jake]

I think it might be more rigid to use two slides, like this (if my ascii art is up to it):


H[ ]H


Where the underlining is the backing of the mirror, and the H's are strips of timber attached to the mirror backing at right angles, carrying the pair of slides (the square brackets) facing each other. The strips would hide the slides from view from the side, too.

 

[CWatters]

What Jake said. Perhaps worth prototyping this before cutting good wood. Make sure that it doesn't bind if pushed down on one side only. Perhaps use one weight and an extra pulley instead of two independant weights? I suspect having the slides closer together rather than far apart would also help.

 

[Dave S]

Thanks for the suggestions everyone.

My present idea as Scott correctly divined is to use counterweights something like the sketch below

So the top pulleys are fixed to the cabinet and the lower pulleys carry the counterweights? If so, then you do realise that each counterweight will need to be the same as the weight as the mirror? Or slightly heavier if you want to overweight it.

Dave

 

[CWatters]

Good point. The size of the weight (particularly it's height) might be an issue. Presumably you have to have a double pulley arrangement to keep the distance the weight travels down.