health mechanic Posted May 19, 2023 Share Posted May 19, 2023 My zehnder unit has insulated 230mm insulated ducts going into a 250 external grill. Exit is in my warm roof on gable end. How are people drilling 250mm hole through standard block cavity walls. Hand drill will not cope with anything greater than 150mm diameter. Don't want to stitch drill as external already rendered. And the big rigs are extortionate to rent and have never used. Any help? Link to comment Share on other sites More sharing options...
PeterW Posted May 19, 2023 Share Posted May 19, 2023 Standard core drill is about £35 a day and they have up to 250mm cores and they charge by the mm wear on the teeth normally. Pilot drill it and then cut outside in, finish from the inside and it’s a 30 min job. 1 Link to comment Share on other sites More sharing options...
TonyT Posted May 20, 2023 Share Posted May 20, 2023 Scaffold though you aren’t doing that off a ladder! Link to comment Share on other sites More sharing options...
Conor Posted May 20, 2023 Share Posted May 20, 2023 I got a guy in with a proper drill rig to do a few holes, worked out at £30 a hole. He did in half a day what would have taken me at least two days of very hard work. The rig was bolted to the wall and drove itself in. Did all the hard work itself. Totally different job from a hand held core driller. Link to comment Share on other sites More sharing options...
health mechanic Posted May 20, 2023 Author Share Posted May 20, 2023 Anyone have details around southampton....I have prices of >400 Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 20, 2023 Share Posted May 20, 2023 Why not just stitch drill it like I do? Use a 4mm sds bit and go around the hole drilling each about 10mm apart. Go to a 5.5m and then a 7mm and a couple of taps with a hammer and 'Bob's your uncle, and Fanny's your aunt'! Start drilling now, and you'll be in the pub by 1 Link to comment Share on other sites More sharing options...
TonyT Posted May 20, 2023 Share Posted May 20, 2023 Plus 1 for above, I hate coring holes, horrible clutchy drill. Especially anything over 127mm 1 Link to comment Share on other sites More sharing options...
Marvin Posted May 20, 2023 Share Posted May 20, 2023 Last week 150mm hole using a 4mm bit in my percussion drill Link to comment Share on other sites More sharing options...
health mechanic Posted May 20, 2023 Author Share Posted May 20, 2023 10 hours ago, Nickfromwales said: Why not just stitch drill it like I do? Use a 4mm sds bit and go around the hole drilling each about 10mm apart. Go to a 5.5m and then a 7mm and a couple of taps with a hammer and 'Bob's your uncle, and Fanny's your aunt'! Start drilling now, and you'll be in the pub by 1 Tempting...but worried about render and quality of finish from outside Link to comment Share on other sites More sharing options...
TonyT Posted May 20, 2023 Share Posted May 20, 2023 You drill from the outside in… 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 21, 2023 Share Posted May 21, 2023 21 hours ago, health mechanic said: Tempting...but worried about render and quality of finish from outside 19 hours ago, TonyT said: You drill from the outside in… Bingo. My bad, was typing and drinking. 🍺 Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 21, 2023 Share Posted May 21, 2023 Also, no guarantees that the render won't pop, even with a diamond drill. Link to comment Share on other sites More sharing options...
Iceverge Posted May 21, 2023 Share Posted May 21, 2023 Get a long (greater than the wall width) bit to make a pilot hole with a slight fall to the outside. This will ensure both holes line up. Drill a piece of 50mm timber with 2x holes 125mm apart. Make the middle one perpendicular to the timber and the outer one slightly angled outwards. Peg the pilot hole to one hole of the timber and use the other hole like a compass for your stitch drilling. It will ensure a neat circle that will be slightest bit conical towards the inside making it easier to chip out. Then get hammer and chisel and get tapping. This can be tedious. Now repeat from the inside. I had 3 holes through 215mm block, 250mm cavity and 100mm block to do. They took an hour each with a cheap SDS. 3 Link to comment Share on other sites More sharing options...
Dave Jones Posted May 21, 2023 Share Posted May 21, 2023 zehndar to a combined inlet and exhaust grill that will more than cover the hole hiding many sins. Link to comment Share on other sites More sharing options...
health mechanic Posted May 22, 2023 Author Share Posted May 22, 2023 Thanks all Link to comment Share on other sites More sharing options...
Mr Blobby Posted February 5 Share Posted February 5 On 20/05/2023 at 08:41, Conor said: I got a guy in with a proper drill rig to do a few holes, worked out at £30 a hole. He did in half a day what would have taken me at least two days of very hard work. The rig was bolted to the wall and drove itself in. Did all the hard work itself. Totally different job from a hand held core driller. Who did the core drilling for you? I need the same for big holes for the MVHR intake and exhaust through dense clock wall. The fitter said he'd kango through and patch it up. I dont think so! Link to comment Share on other sites More sharing options...
Conor Posted February 5 Share Posted February 5 Core master. Think £250 for two guys and their rig for half a day. That was enough time to get setup and 5 large cores drilled through 150mm and 200mm RC. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted February 5 Share Posted February 5 If you're not too far is massively simpler to just build in the duct to the block work. Link to comment Share on other sites More sharing options...
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