How to fasten a hinge to granite?

[Dell Littlefield]

I have a piece of granite counter top I would like to use in a drop leaf table. I want to have a white oak leaf on each side and a similar width piece of oak on each end. I'd like recommendations on type of hinge and method of fastening to the granite. Also, could I get away with epoxying the ends directly to the granite with no other support? All of the wooden parts would be about 7 1/2 inches wide and 1 1/4 inch thick. One more question, I'd like to use a center column to support this. This would leave about a foot of granite with no support under it. Would that work?

[Dan Hintz]

Epoxy would appear to be a valid option (assuming a piano hinge with a lot of surface area). Is something like this typically done with the hinges being attached to a wood base and the granite attached to the wood? Gives more surface area to hang onto the stone.

[Dell Littlefield]

Thanks for your help, I did not want to underlay the granite with wood or plywood because: 1. The edge would be exposed when the leaf was down. If necessary to underlay, I suppose I could put a matching wood border around plywood. 2. This would require a thicker leaf (about 2 inches). Any comment on the column support?

[David C. Roseman]

[snip] I did not want to underlay the granite with wood or plywood because: 1. The edge would be exposed when the leaf was down.[snip]

Dell, don't know if it's the best way to achieve your ultimate goal, but I'm puzzled by this specific concern over wood underlayment. Perhaps I'm visualizing this incorrectly, but if a strip of wood (or other material) were fastened along the hinged seam on the underside of the granite, and a piano hinge secured to the edge of the strip under the granite (hinge joint up) and the bottom of the drop leaf, why would anything other than the finished edges of the granite and drop leaf (and the joint of the hinge) show in the down position?

David

[Dell Littlefield]

I was referring to the edge of plywood underlayment showing. If I bordered it with solid wood, it wouldn't look bad but would require a thick leaf. For example, the granite is 1 1/4 inch thick, with a 3/4 inch support piece would require a 2 inch thick leaf. If I can figure out some way to attach the hinge to the granite, I can get by with a thinner leaf.

[Judson Green]

I would definitely use a sub top (underlayment) and dress up the edge as you see fit, a bit of cove or something from the borg, a bit of stain or paint. Not only will it allow for a better place to mount the hinges for the drop leaf. But really its the overhang and center column that you want to use that leave the counter, well not very well supported. Granite counters, and other natural stone, have lots of little fissures, like small cracks, in them running all over the place. Not to mention the poor tensile strength, not a good beam. And let's not for get the weight ~18 lbs a sq ft (depending on density and thickness). And for whatever reason a overhang on a bar/counter invites someone (maybe a really large someone) to aggressively lean on the top, or worse sit on the overhanging edge. Or worst yet a large personal injury attorney.

Adding the sub top won't necessarily make these issues go away buy will provide for more, nearly full glue contact on the underside. Kind of like how plywood gets its strength, the glue bonding many layers together.

Might you have a sketch?

[Jerry Miner]

I was referring to the edge of plywood underlayment showing. If I bordered it with solid wood, it wouldn't look bad but would require a thick leaf. For example, the granite is 1 1/4 inch thick, with a 3/4 inch support piece would require a 2 inch thick leaf. If I can figure out some way to attach the hinge to the granite, I can get by with a thinner leaf.

I think David (in reply #4) was talking about this: (one picture is worth a thousand words)

Drop Leaf 9-5-13.png

As you can see, the leaf does not need to increaase in thickness in order to avoid exposing the sub-top.

[Jeff Duncan]

I'm going to skip the hinge question and go directly to the think this through carefully point. A 1-1/4" slab of granite is very, VERY HEAVY! I can't stress that enough. Make sure you have this project well though out as a single column can be tippy if not wide enough at the bottom. Now add a couple extensions, or let's call them 'levers' for now, and that base needs to become even bigger! I'm not saying it can't be done, but just make sure you've thought through all the potential issues, (like someone half sitting on the edge), as a granite table falling onto someones leg.....well that would be bad

good luck,
JeffD

[Dell Littlefield]

Lot of valid points here, thanks. I may have to give up on the central column idea. The granite slab is 25 X 30 inches, I think it weighs about 75 to 80 lbs. I planned to add 7 1/2 inches of wood on each side resulting in a top that is about 40 X 45 inches. The drop leaf would be in the long dimension. Thanks for the sketch, Jerry, if I mount the hinge as you depict, do you have any suggestions on how to support the leaf? Reckon I'll have to buy some Rockler workbench casters to move it?

[Mark Bolton]

I dont think you'd have any problem drilling and epoxying inserts into the granite to facilitate a direct mount of the hinge. Counter top fabricators do it all the time. And I wouldnt be concerned at all about the strength of the granite either. Its not uncommon for top fabricators to cantilever a 10-12 inch span unsupported. Thats a lot of weight that could be put on that lever when you think of a 350lb whopper with cheese leaning on the edge of that overhang (forget about a whole family's worth).

What I WOULD be concerned with is, is it worth the effort? Accurately boring and epoxying fasteners in any masonry or stone surface is a nightmare. Then you have the issue of mortising, alignment, and my major fear would be the fastener/insert being so close to the edge it could potentially blow the face/edge out if it fails.

Your central column doesnt seem that far of a reach either for the size of the table your building provided you have enough spread at the base.

Ill bet if you spend some time sketching it out in detail or in Sketchup you'll work your way through it.

[Joe Kieve]

Here's another thing you might think about. Build a frame out of 2X2 oak. Rabbet the inside edge 1 1/4" deep, miter the ends or half-lap them, put it together like a picture frame, them drop the granite in. You'll then have the ends and sides with wood to hinge any way you want. You could even put plywood on the bottom to give you something to attach the base to.

Just my 2 cents.

[Judson Green]

I dont think you'd have any problem drilling and epoxying inserts into the granite to facilitate a direct mount of the hinge. Counter top fabricators do it all the time. And I wouldnt be concerned at all about the strength of the granite either. Its not uncommon for top fabricators to cantilever a 10-12 inch span unsupported. Thats a lot of weight that could be put on that lever when you think of a 350lb whopper with cheese leaning on the edge of that overhang (forget about a whole family's worth).

What I WOULD be concerned with is, is it worth the effort? Accurately boring and epoxying fasteners in any masonry or stone surface is a nightmare. Then you have the issue of mortising, alignment, and my major fear would be the fastener/insert being so close to the edge it could potentially blow the face/edge out if it fails.

Your central column doesnt seem that far of a reach either for the size of the table your building provided you have enough spread at the base.

Ill bet if you spend some time sketching it out in detail or in Sketchup you'll work your way through it.

Ive seen fabricators drill into the stone for mounting of a sink, a static load, not for a dynamic load, like the hinges. Huge difference. As to the cantilever I've seen it done but I wouldn't do it or suggested it. At least some brackets, corbels or something. Just saying better safe than with a 80 lbs stone dropping on my toe from 36".

[Jerry Miner]

if I mount the hinge as you depict, do you have any suggestions on how to support the leaf?

One approach would be a sliding support bar, like this:

Drop Leaf Support 9-5-13.png

[Dell Littlefield]

Lots of good ideas and suggestions here. I am going to talk the foreman of the granite outfit that installed my counter. He has a lot of experience and may have some other good ideas. Thanks everyone, keep the suggestions going, I have plenty of time for this project.

[Dan Hintz]

One approach would be a sliding support bar, like this:

Drop Leaf Support 9-5-13.png

I like this method the best, so far... I always seems to whack my knees on the swing-away corbels.