Good afternoon, SF.

I have a small piece of granite here -- almost exactly the size and shape of a sink cutout -- roughly 1-3/4" thick.

I've received a request to turn it into an end table.

Being the geeky engineer sort, I designed a frame for it using 80-20 aluminum extrusions. I'm happy with it, but it's going to be more expensive than it ought to. The benefit: I don't have to weld -- my welding skills are horrible. It's simple -- just four legs from the 1" extrusion, plus four lateral pieces in between them to add some stability.

Whether 80-20 or a welded frame, I'm all set until I get to the point of "let's attach the granite to the legs." With the extrusion-based frame, I figure I can tap the top of each leg (1/4-20) and thread in a piece of threaded rod to stick up about an inch. With a welded frame I could do similar, though we'd have to weld a drilled and tapped plate into the top of each leg.

With either style, my next thought is to drill four pockets into the underside of the granite (I'm figuring 3/4" diameter, an inch deep), fill the pockets with an epoxy of some sort, turn the frame upside down and set the threaded studs into the pockets. Let the epoxy cure, and all should be well, right?

That's the point where I stall. I see plenty of articles on the web about drilling through granite with a diamond hole saw or such, but I haven't yet seen how to drill a pocket instead of drilling through.

What's your guidance, ladies and gents?

High speed hammer drill. Very gently. Use water to keep the hole cool and clear. Drill the smallest hole possible and epoxy threaded bushings into the holes. ⅜" to ½" hole. Smaller is safer.

A carbite-tipped drill bit on regular 'drill' would take longer but be gentler. Water to keep it cool. You can make a 'water dam' using plumbers putty.

I *never* drill into customer countertops because there's too much liability. People want me to anchor a dishwasher, nope, I figure out something else.

Have you considered epoxying the top to the frame without drilling and screws?

There are brackets used for mounting under counter sinks. They are wedged into a groove machined/ground into the bottom of the granite slab. These grooves are made with a diamond wheel mounted on a common 4 1/2" grinder, and only go about 1/2" deep into the slab. Perhaps these could be modified to accept your bolted on legs?

quote:

Originally posted by arfmel:
Have you considered epoxying the top to the frame without drilling and screws?

If the stone has a dropped edge, use a piece of plywood for a base to aluminum then epoxy the stone to the wood.

I personally wouldn't mess with drilling the stone the way described.

It was referenced once already, but I feel it is important to say it again.

If you are not experienced using a hammer drill, practice on “something” first.

They are exceptionally loud and as said, let the drill do the work.

quote:

Originally posted by arfmel:
Have you considered epoxying the top to the frame without drilling and screws?

I hadn't, honestly, but the top of the frame is simply the ends of the extrusion. There's not much surface area there to glue onto.

quote:

Originally posted by architect:
brackets used for mounting under counter sinks.

I'll look into this. Thank you.

quote:

Originally posted by LS1 GTO:
If the stone has a dropped edge, use a piece of plywood for a base to aluminum then epoxy the stone to the wood.

There's no dropped edge -- it's just a flat slab.
But putting together your suggestion and arfmel's, I could bolt a strip of angle aluminum to the front pair and the back pair of legs, increasing the surface area onto which to epoxy the slab. That's far better than having to drill this piece. Perhaps even drill some "lightening holes" into the top of the aluminum, further increasing surface area and giving the epoxy a bit more to key on.

- - - - - - - - -
ETA pics.

The intent:


The top of the frame:


Top of the extrusion:


Revised frame, after LS1 and arfmel suggestions:


- - - - - - -

So in short, the answer to "how should I drill into this small slab" is, "find another method."

I *think* the shops which do fabrication run everything on air. Lots of water. Yellow slickers quantities. A high speed bit with lots of water, possiby even CNC-drilled.

This is a wet/dry bit but I'd think you'd need a jig clamped onto the countertop. It is made for exactly what ypu want to do.

https://www.homedepot.com/p/Mo...e-SCB0012D/303018701

Working from the revised frame picture, the last one, add those same brackets along the two longer open sides to create a continuous frame that will contact the underside of the stone all the way around. Then run a bead of heavy duty construction adhesive all the way around and set your stone.

The weight of the stone is doing most of the work at keeping itself in place. The glue will keep the stone from shifting or falling off the base if bumped or jostled and will insure the legs come along for the ride if the table is picked up.

Anything beyond that is over engineering and an opportunity to damage the stone.

Run 100% silicone around the edge that meets the slab. Once it cures, it shouldn't move.

quote:

Originally posted by TXJIM:
over engineering

Nooo, I'd never do that!

quote:

Originally posted by petr:
Run 100% silicone around the edge that meets the slab. Once it cures, it shouldn't move.

Can do!

I should add that if you can put angle iron around the whole thing to add more surface area for the silicone to grab the better. So long as you are aware of this when moving it so it doesn't loosen up if jarred.

I can do that.

I'm thinking once they place this table, they won't be moving it much.

Also. Use aluminum angle to match the aluminum frame. The whole dissimilar metal thing.

Do NOT use a hammerdrill for such task.

Diamond tip bits using a regular drill (high rpms) will work better, without the added risk of cracking the slab.

Once someone uses diamond tip core bits with a grinder, the hammerdrills end up sitting in the shop.

I had a guy come in to drill a hole in our counter. He charged me $25. That's how I'd recommend doing it.

quote:

Originally posted by vthoky:
I can do that.

I'm thinking once they place this table, they won't be moving it much.

You'd be surprised what a woman can accomplish when she has some strong backs, with weak minds, at her disposal/ under her influence.

3M 5200 adhesive...comes in a tube like caulking...glue some type of angle bracket to the bottom side , let it cure and attach the legs.

quote:

3M 5200

Got it! Thank you.

as a boat builder I love 5200. But for home stuff its probably not the best possible choice. At a minimum you want 5200 fast cure, you will distinctly be unhappy with the cure time of normal 5200 for this. Second if you decide to bond the al to the granite then you might look into Loctite PL s40 as it has a reputation of being better in the al bonding, but has the same cure time issues as 5200. Third, if at all possible in your design I would bond wood to the granite and then fasten the Al to the wood if it allows you a bigger surface area for bonding.