How do I cut a 7.25 inch hole through a wall?

[Pete]

Hi.

Does anyone know of a good way to cut a 7.25 inch (185 mm) circular hole through a wall?

I have attempted to hire a hole cutter but they seem to stop at 6", which is definitely too small.

The depth and nature of the wall is an additional problem. It is about

12" thick, and is made up of two 4" rows of breeze blocks with an insulation-filled cavity between them. The breeze blocks are faced with masonry on the outer wall, and plaster on the inner wall.

Drilling a circle of holes and knocking out the core would, I imagine, be pretty tricky in terms of lining up the drill holes given the depth of the wall. It would also be time consuming, and the end result would be ragged.

Any suggestions for better methods would be welcome - particularly if someone knows where I might hire a hole cutter big enough to do the job! (I live near Norwich, just in case anyone knows anwhere local to me.)

Thanks.

[.]

HSS do a 200mm diamond drilling rig £96/day +VAT

[The3rd Earl Of Derby]

Sir Benjamin Middlethwaite

[Dave Baker]

I presume you mean render. Masonry is brick or stonework.

The type of wall makes this easy rather than hard. Breeze blocks cut like cheese. If you make a rough hole by whatever method comes to hand you can clean it up with a carbide burr in a drill until your pipe, flue or whatever fits through.

You do one layer of blocks first, say the inside one, mark the centre and drill a pilot hole through the outer layer, go outside and mark your 7.25" hole around that with a compass or pencil and string and then cut that hole out from outside. Everything should line up fine but once it's all been plastered and rendered back round whatever it is your fitting through this hole it'll look perfect whether the holes were ragged or not.

-- Dave Baker

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[The3rd Earl Of Derby]

I certainly would not lay out £90 to hire a tool thats going to be used once in an hour. :-(

I would cut a square to the diameter of the circumference, fit the pipe? and the fill the four corners with cement pushed in with a stick till it was solid packing.

-- Sir Benjamin Middlethwaite

[.]

the OP might.

time is money and if I wanted to avoid buggering about for x hours and I wanted the job done /quickly/, /neatly/ with /minimum effort/, in 1 hour leaving the other x hours to do something else I would pay the £96+ vat.

[The3rd Earl Of Derby]

Since its breezbloc I suppose a tool could be made from a piece of 1" x 7" long steel flat bar like this ^-----^ the middle grinded away and a short steel rod welded to the bar for inserting into the drill chuck.

-- Sir Benjamin Middlethwaite

[Pete]

Thanks for all the suggestions.

=A390 for one day's hire of a hole cutter is definitely more than I would prefer, but I tend to agree with the comment that it would be worth it to get a fast, easy and neat job. However, I checked with HSS and they advised that the suggested cutter was for cutting holes in floors and would not cut a horizontal hole through a wall.

One further complication has arisen - I have now been told that the outer course of blocks might be concrete, and thus (presumably) considerably harder to cut than breeze blocks.

Interesting suggestions from The3rd Earl Of Derby and Dave Baker. I have also received a suggestion that cutting holes 2 or 3 inches in diameter around the perimeter and grinding down the small pieces of block left between the holes would be a faster way to go. This method appeals, but I am not sure what might be the best means to cut away the pieces of block if the outer blocks are indeed concrete. I guess I could simply cut out the perimeter of a larger hole than I need so that the pieces left wouldn't obstruct the pipe I am installing, but I would prefer to make a neater hole than this if possible.

Does anyone have any opinion on this method, and a suggestion of how best to cut away the pieces of concrete block left between the small holes around the perimeter of the large hole?

Thanks.

[.]

such drill rigs are available. I've seen them being used.

google search: horizontal drilling rig 200mm

a bit of ringing round, you will find one. alternatively, give this lot a ring / search their site someone in your area will be able to quote you for doing the job.

if the outer wall /is/ concrete your best option /is/ diamond drilling.

[Mungo "Two Sheds" Toadfoot]

Having read the suggestions put forward so far, and attempted to make a few neat holes in brickwork myself, I wonder how much it would cost to get a bloke in who's got the gear and knows what he's doing? Not in the spirit of DIY, of course, but when a job could be expensive *and* difficult...

Si

[T i m]

Based on those plastic drill jigs you get for chain drilling electrical socket metal back boxes howabout this.

As an exansion of what Dave Baker suggested ..

Drill right through at the centre of the proposed hole with (say) a

10mm dia long bit. Maybe use a square on the hole as you start to ensure it's a square to the wall as you can get.

Get a lump of 8 x 2 sawn (or similar) and scribe yer 7.25" (or maybe scribe it at 7" or whatever depending what sort of final fit you need) and using a pillar drill, drill through yer scribed line a series of holes the diameter of your long drill bit tip at regular intervals around the circle. I would leave half the diameter of the drill bit between the hole to try to stop the holes breaking into each other till you were ready (especially on the inner layer).

Counter bore the middle and use a long 10mm Fischer plug / screw to pull it tight to the wall then drill through your gide. You could possibly slacken the fixing screw and rotate your guide to get inter spaced holes?

If you didn't want to go right through in one go go half way (mark the drill shank with red tape) and repeat on the inside.

Revove yer drilling jig and redrill at a slight andgle (from both directions) to join the holes together. When sufficiently broken away you could probably use the drill bit like a router and cut the remaning 'bridges' away till the plug falls out ;-)

Trim up with suitable half round 'universal' rasp ;-)

Look at the two plugs, the pretty neat hole through yer wall and go down the pub with the 100 quid! (or use it to buy a half decent SDS drill and a couple of long 10mm bits that you can use on the next job) ;-)

All the best and have fun ..

T i m

[.]

one has to wonder why the diamond tipped core drill was invented and why drilling rigs were invented and why hundreds of enterprising people have bought drilling rigs and franchises for drilling concrete :o)

about the only inexpensive solution for the OP is to scribe a circle on the outside wall, drill a hole in the middle right through the outer and inner walls to give a reference, repeat the circle scribe on the inside and then drill series of holes around the scribed circles until the desired ~185mm hole is achieved.

as for finish, it's only the outermost 2 or 3 mm which has to be perfectly circular as the render / plaster will do what it's desigend to do: hide the underlying imperfections from a critical eye which most people don't have.

personally, hire the rig or I'd get someone in. someone who does a job day in, day out usually produces a better result and there are times when even the most avid DiYer needs to box a job off by paying someone else to get the whole project over a time consuming obstacle.

[T i m]

Yes, that is less expensive than the additional offcut of 8 x 2 but then he has to ensure every hole doesn't run off as it starts or break into an adjacent hole and that each hole is perpendicular to the wall by eye (rather than having a jig that gives him a feel that he's drilling in the right direction?

Assuming he wan'ts to tidy up the rendered finish?

True ;-)

I'd see that particular job as a bit of fun ;-)

The challenge would be if the outside was accessed by trying to stand on a 45 deg roof .. ;-) Thanks goodness for ladders and scaffold boards ;-)

All the best ...

T i m

[.]

because people who's time is money want to save time and money ;-)

it's only the outer skins that need to be perfik.

very true.

I'd see the hiring of a new bit of kit and boxing the job off in a couple of hours as both educaional and sensible. I've done far too many 'bit of fun' jobs (which paid well) to be wise enough to pay others to do em these days. mebbes I'm getting soft :-(

aye, praise alan [pbuh] for my sacred scaffold tower :o)

reciprocated :-)

[John Rumm]

Last time I needed to do something like this I stuck a 10mm hole right through the wall and used it as a center to mark a suitable circle on each side. Chain drilled round the edge, and then joined the dots with a

20mm chisel in the SDS. Once the pipe was in place and a bit of mortar around it looked plenty neat enough.

[Rob Morley]

Stick a big Rawl bolt fixing in the middle of where the hole should be. Screw a length of studding into it (or better if you can, get a long bolt with a smooth shank, and cut the head off) - it should stick out a few inches further than the length of your masonry bit. Take a piece of

3x2 or similar and drill one end to be a sliding fit on the bolt, the other to fit the neck of the drill. Cut a slot at the drill end and fit a couple of screws or bolts either side so you can clamp the drill firmly. Mount the drill in the wood, and slide it onto the bolt - wherever you drill will be pretty much the right place :-)

stud or long bolt fitted to Rawl bolt anchor drill

| | | | | | \ / _____| |___________________________\ /_______ | | | | | | | | | (|) | | (-) | | | | | | | | | | | | | | | | (\) ------------- (/) | |_____| |____________________________|| ||________| | | | | ^ | | | | | | | \ / | | | \ / clamping screws | | ------- or bolts | | | | | | | | ====================================================================== | | | | ||

[Chris Bacon]

If it's just one hole, something like this would do it:

you want several holes done at once, use one of these:

also be useful, but warn the neighbours first, and use plenty of dust sheets to cover furniture, etc.

[The3rd Earl Of Derby]

PMSL I make it six holes on the last one. ;-)

-- Sir Benjamin Middlethwaite

[Pete]

neat hole I was hoping for...

Anyway, thanks for all the advice.

I have created the hole today, and all went well. In the end I used a technique that was a combination of the advice I received. I hired a core drill (with various diameter bits) and bored a series of interlinked 2" holes around the perimeter of a 7.25" circle on the inner wall. I used my own SDS chisel to remove the remaining masonry around the periphery to leave the desired 7.25" hole.

wall from the centre of the 7.25" hole, and scribed a 7.25" circle on the face of the outer wall using a measured piece of string tied to my

8 mm drill bit.

The inner wall had been a lot tougher than expected - not just a normal breeze block. When drilling my 8 mm hole I had found that the outer wall was even harder, and it would have taken a long time to bore seven

2" holes throuth it. I therefore chose to bore a single 6" hole (the largest diameter borer in the kit) in the centre of the 7.25" scribed circle on the outer wall, and then used the SDS chisel to remove excess material.

Things went very well. The holes in both the inner and outer wall blocks were pretty neat. Not as neat as a bored hole, but not far off. The gaps left around the pipe will be easily filled.

Again, thanks to everyone who contributed; your advice enabled me to assemble the right equipment in advance and use a technique that produced a good result. It didn't take long to do, either.

Cheers.

[The3rd Earl Of Derby]

Good stuff.

pmsl today when i was in the Asda today...

I was looking for a new sauce pan and me brain started wandering, I picked up a steel sauce pan which was about 7" and me mind went back to this thread. What if I took the handle off this sauce pan, sharpened the rim on the grinder and drilled a hole in the bottom for the scarret holder mount...would it work?

Bearing in mind it was a thought just for breezebloc. lol

-- Sir Benjamin Middlethwaite