Diamond core drills.
 

I need one, 78mm, for about half a dozen to a dozen 40mm deep holes in stone walls in France.

I've found them on ebay at £13.63, I already have an arbor.

After that they rise to £22.50, same size. My question is, will the cheaper one be ok for a dozen or so holes?

http://www.ebay.co.uk/itm/TURBO-LASE...item3cb96effd4

or, http://www.ebay.co.uk/itm/Diamond-Co...item19c5604e13

Without actually looking at the links I'd advise against cheap ones. I cut hole in walls all the one to install pipework for A/C and fridge units. I paid about £35 for one 2" cutter and it's awesome. Bought it from a Makita outlet but it's not made by them. I can't remember who did but they're yellow! I'll have a dig about to see if I can find who it was.

Edit: just looked at the links. First one looks very similar to what I have. Same notches in the "teeth". Stone will be tough enough to cut no matter what you have. Whatever you do, don't wet them!

Don't wet them? Why not?

I can choose where I cut the hole so as to cut the edges off smaller stones rather than a hold through a stone. If any come out of the wall, no problems as I have to point up, so can introduce some of the smaller waste to fill any voids.

Basically, it's to sink 68mm plastic boxes for sockets, the wiring comes in via flexible conduit also hidden under the pointing.

U get what u pay for. Personally I would get a half tidy one, or even hire one, I don't know what it's like to hire in France but in the UK there are loads of tool hire shops

Difficult to hire what is, in effect, a consumable.

For the hire cost it's best to just buy it. They charge silly rates per mm or half mm of wear.

Firstly don't wet them because the manufacturer says not to (in my case) and secondly because I did it anyway and it does nothing but clog the cut with crap that quickly turns to a paste which causes the core bit to get stuck. From experience, let the core bit do the cutting, clear dust regularly, don't push it hard and use a drill which has some kind of clutch so you don't get your wrists broken! We bought a drill from Makita specifically for the job and it made a hell of a difference. I've successfully used my battery drill with them too.

Last core drill I hired was fecked.

I bought a cheap 5 piece set for £90 from these guys via their amazon store: http://www.moorcut.co.uk/about-us

I only wanted it for a few sets of holes and I've got to say I'm more than impressed, nice quality, and it all came in a air -hostess style trolley case.

Diamond core bits
 

It all depends on the type of stone you are cutting, the harder the stone the the softer the compound you need in the bit, I.E Sandstone you need a hard compound as it's very abrasive and would wear the bit very quickly, 20yrs in business diamond drilling:-)

Steve

Cheers. The walls are randowm stone, with loose fill centres. Stones range from mica to vary granular to quartz. I'd obviously NOT be drilling quartz if I could avoid it.

So far I've got away with it twice by using an SDS drill to drill a circle of holes, linking the holes with a chisel in the drill, and knocking out the centre with a cold chisel....but it's laborious and hard work. I have to do about another 8-12 pairs of holes for double sockets, just was looking for an easier way.

Doesn't have to be neat, the back boxes are plastic and get mortared in with lime mortar, the conduit goes under lime mortar too.