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drilling granite worktop

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Terry - Somerset

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These are for materials which on the MoHs scale are below 5 - eg: marble is about 3. Granite is usually rated at 6-7 so I suspect they are unlikely to be much use.

Not actually sure of the answer - it may be that a local worktop supplier may give some advice as it is not an unusual requirement.
 

Phil Pascoe

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I can't see why any diamond hole saw wouldn't go through a granite top - we use them to go through random stone walls and concrete blocks which are full of pieces of granite, granite being what the area is made of. They'll go through blocks with elvan chippings in them, which is harder than granite.
A cheap one won't last long but so what if it serves your purpose - you're not doing the job day in day out.
 

Eric The Viking

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^^^ Wot Eee said (as usual!).

Slow speed, water lubrication (if you can contrive that) and/or dust clearance, probably quite a lot of "remove-drill... clean... continue". If dry, you need to have a vacuum running to remove dust as fast as possible and keep the hole as clean as possible.

I'd do the pilot hole first - it will give you a feel for the material and a chance to correct any alignment before cutting the perimeter of the hole. Drill through electrical or masking tape to get the pilot started (stops skidding). For porcelain glazed tiles I also use a big masonry pin to indent the surface, as masonry bits have a blunt point and/or an offset centre - infuriating if you want accuracy. You should be OK with just tape, but if not there are cheap diamond burr sets available that would do the same thing. If you use carbide for the pilot hole, that drill WILL heat up. I can't be the only person to find I was trying to drill using a bit with no carbide tip on it any longer! Slow speed, NO hammer action, etc. You just have to be patient

The big issue with diamond hole saws in my experience is clogging and then jamming. I have a really large one for doing extractor fan ducting, and you have to be rather careful driving it because it will jam easily. I've been very grateful for the slipping clutch on my Makita SDS (and I think I knackered it using the diamond core drill!).

I've had good results with the Marcrist brand. The smallest I have, however, is 40mm, which gets used for bath and basin waste pipes, and through building materials (usually not granite! It's limestone mostly round here, which is softer). It would be no good if the hole was on show though, as it's way too large to look neat. Smaller ones are available. But there is a trade off between snugness and difficulty of alignment - probably worth allowing 5mm on the diameter as a compromise.

At a guess (and it IS a guess) anything suitable for porcelain ought to do granite too - after all diamond tooling is what's used in the factory to cut and polish. That said, the size of the diamond particles probably matters - tooling for brick and blockwork is possibly too aggressive for granite.

By the way, it's not impossible, by any means. This is how it used to be done by hand (top left) - thump, rotate, repeat:

 

RogerS

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To stop the drill bit wandering I sometimes make an identical hole in some MDF or ply and clamp that in position as a guide.

Rubi also do a rather neat gizmo that has a large sucker and a water feed built into a V-shaped guide that also works well.
 

MikeK

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Two years ago I had to bore a 45mm hole in a 40mm thick granite surface. I used a core drill similar to these:

https://www.atsdiamondtools.co.uk/produ ... esaws-m14/

We knew this was going to take a long time, so I mounted my Wabeco B1230 drill stand on a double thickness of 19mm plywood, with the drill mount turned 180 degrees from the base. After drilling the 45mm pilot hole in the plywood using a hole saw, as RogerS described, we changed the cutter and positioned the rig where we wanted to bore the hole. There was another piece of plywood on the bottom surface of the granite in hopes that it would prevent chipping or damage as the core drill exited the slab.

Since the plywood was sacrificial and was needed for only one hole, we didn't care about water damage once the boring started. I think it took about 30 minutes to go through the granite, with frequent progress checks and adding water to the cutting area. The exit edge was clean, but I don't know if this was due to the plywood backing or because we took our time. We didn't realize we had actually gone through the slab until we retracted the core drill to add more water.
 

Paul200

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Hi Marcros

I would endorse everything Eric said, with the addition of Roger S' comment. You need an industrial diamond core bit of reasonable quality (Marcrist are good). Don't mess about with the holesaws - they're just not up to the job. And don't use a TC core bit - these are designed for hammer action only and you don't want to use that on a worktop! With that in mind, the pilot bit for use in a diamond core is TC tipped and, in granite, you could be spinning that drill for ever in rotary only mode. I would take Roger S' tip and use a pre-drilled piece of mdf as a guide, clamped hard to the worktop, and dispense with the pilot.

Take it slow, don't use hammer action, don't force it (you actually slow down the process), use a drill with a clutch (if you value your wrists) and keep everything cool (frequent breaks and a wipe down with a wet sponge). Also ensure that the core size will give clearance for whatever it is you're fitting in the hole - you don't get a second go!

Good luck!

Paul (ex tool shop owner and dispenser of free advice)
 

flying haggis

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"keep everything cool (frequent breaks and a wipe down with a wet sponge)." but what about the drill bit......................
 

Bod

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flying haggis":2vemddut said:
"keep everything cool (frequent breaks and a wipe down with a wet sponge)." but what about the drill bit......................
Give a beer after the job.

Bod.
 

D_W

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ditto to above - a hole saw type that uses a pilot hole for alignment.

If the holesaw is diamond and relatively new, you'll be surprised how fast it goes through granite. Fairly sure the advent of cheap granite counter tops has much to do with how much cheaper (chinese import) shaping tooling is for granite.

Neighbor had a two man shop custom cut, shape and deliver/install about 20 linear feet of granite two weeks ago for $2100, less than the cost of the blank unshaped countertops about 15 years ago, and typical cost was 3 times as much once you added shaping and installation.
 

Sideways

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If you have a one of the handful of Metabo drill models blessed with "impuls" mode, this is perfect for starting a pilot hole into glass, ceramic and no doubt granite without the bit skidding and having to risk the adhesive tape trick.
Switch to standard action once the hole is started.
 

Phil Pascoe

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D_W":3bkp86kl said:
Fairly sure the advent of cheap granite counter tops has much to do with how much cheaper (chinese import) shaping tooling is for granite.

Neighbor had a two man shop custom cut, shape and deliver/install about 20 linear feet of granite two weeks ago for $2100, less than the cost of the blank unshaped countertops about 15 years ago, and typical cost was 3 times as much once you added shaping and installation.
A late acquaintance told me he could buy granite gravestones from China cheaper than he could cut the granite out of his own quarry.
 

Geoff_S

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Quite by coincidence. I refitted my kitchen 2 years ago which involved removing the old granite which has been leaning against a wall for the last 2 years awaiting my plans for it.

I've finally got round to dealing with the intended project. I've got one piece that's 2100mm x 700mm and I want it polished on all edges
and a hole diameter 550mm. It's to be a table top for a kettle barbecue.

There are 3 other large pieces that I also want cut and polished on all 4 edges.

So, I of course considered doing this myself, how difficult can it be? I have absolutely no experience and if I get it wrong? And I have no intention of ever doing it again.

So, I contacted a local granite mason (is that the term?) and he's going to cut and polish a length of 16 metres in total, plus a 550mm hole with polished edge and the circle that's cut out also polished. And he's going to do it all on site. All for £360.00!

Have you considered getting a professional to do the cut? Just wondering.
 

marcros

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I don't know of any pro but I did think about it. The project has been pushed back a bit because I have a greenhouse arriving 3 weeks ahead of expectation and some gravel arriving sooner than expected too. I need to get some ply and some metalwork sorted for the table.

I want to go and measure the parasol at Costco when I next go to check the size, it is stated as 38mm online and I had misremembered it as being 2", so the hole will be a bit smaller.

I am tempted to take it slowly and do it myself, starting the hole using an MDF or ply template. The seller of the diamond drill that I linked to said that it is fine for a one off hole. I might drop a line to a pro and see what the cost would be before I buy anything. It would probably take me as long to take the piece somewhere and back than to do the job myself.
 

Phil Pascoe

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Drill a bigger hole and make a grommet to take up the slack. If you make it to accept a 38mm tube and at a later date you want to use a larger one you'll have a pig of a job cutting it again.
 
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