What hinges can I use?

[dilligaf76]

I have a square hole in the concrete floor and I want to cut down to size a paving slab roughly 40mm thick to fit perfectly inside so the surface is flush with the rest of the floor but I want this paving slab to be hinged so I can open it about 90 degrees, however I want a hinge that can be fixed on from underneath so that there are no protruding parts from the top.
Obviously I cannot just use a normal hinge underneath as the pivot point would be in the wrong place and it wouldn't open.
I hope one can understand what I mean... what hinges can I use for this?

 

[He who knows]

Any point looking for hinged manhole covers? Or (as I guess) is the size so non-standard that you'd have no chance?

All I can think of is cutting shallow rebates in the floor and slab to allow hinges to lie flush.

Finding ones strong enough to take the weight may be another challenge....

 

[dilligaf76]

There's something out there it's just the case of finding it. The weight shouldn't be an issue really as it's only about 16 inches by 12 inches so not all that heavy considering the size of it!

 

[He who knows]

Ah - OK - I was envisaging something large enough to climb down through.

No - I have no idea why I was.

Will you need to open it frequently? Does it need to be hinged? What about a recessed frame it sits on, with a keyhole slot in it and you just use one of those manhole cover handles to lift it out?