Using a diamond core drill

[Dippy]

I'm planning to install an air-conditioner so will have to drill a 90mm hole through a cavity wall (brick & concrete block). I have done lots of DIY but not this job. Based on a bit of research I think that I'll buy a diamond edged core bit rather than TCT because even though it's only the one hole I'll pay the extra for less effort. I already have a 1.25KW SDS drill with clutch (yes I know I must use it with hammer off) so I think I'm good to go. Except for one thing - the air conditioner is to be fitted to an upstairs room.

I have read advice that it is a good idea to drill from both sides, however even if that is not essential I assume I would get a cleaner hole by drilling at least a little from the outside. But that means using a ladder (I am certainly not hiring scaffolding just for this job!). The instructions on my drill state that it has a clutch but that it still needs to be held firmly for it to operate and that I should never drill from a ladder. Is this 'over-cautious' advice or should I definitely rule out doing any drilling from the outside?

I have done lots of chasing on the inside so I'm OK about screening off the wall to contain the dust, and I guess I'm not too bothered about the outside hole being a bit ragged when I cut through as the air conditioner umbilical and condenser unit are hardly attractive.

Also the instructions say that the hole should be at a slight angle downwards. Presumably I just need to start the drilling slowly and carefully whilst only one side of the cutter has any contact?

 

[catlad]

If you decide to ignore the advice about drilling of a ladder then get someone to film you, and then we can put a link to you tube as to why it is not a good idea.

 

[RF Lighting]

I always drill all the way through from one side only.

If the hole is at low level I'll drill from outside to keep the dust down, if not then all the way from inside.

Using a diamond corer produces a brilliant clean hole, and breakout will be no more than a couple of mm bigger than the actual hole, and will easily cover over with the external grille.

 

[Dippy]

Thanks for the replies - from the inside it is then.

 

[ibruceuk]

I have done both.

That is drilled from one side only and from both.

The breakout as said is minimal, particularly if you ease right off with any pressure as it's getting close.

I've also drilled off a ladder (I know, I know). My tip would be make sure that the ladder is tied off completley so it won't budge and make sure that you are incredibly well braced so that you don't get thrown off.

As long as you are prepared then it's fine.

 

[Dippy]

Closing the loop on this for the benefit of people like me who might search the subject.

I drilled my hole yesterday - from the inside. As I noted, I have never drilled a hole with a core drill bit before and so here are my tips for other newbies:
1) Dust. There will be a lot so if you are drilling from the inside you'll want to do something about it. I used a dustsheet to create a 'cubicle' around the area I was drilling. I also fixed my diy vac floor adapter to the wall below the hole. My vac is the type with a power outlet and the vac turns itself on and off when power is drawn (i.e. in response to using a power tool). This way I minimised how much dust got away.
2) Starting the hole. I drilled a pilot hole but it was still hard to get the thing started. So I took the core bit off the drill and started the hole by hand. As this was the inside it was just plaster, so by hand I was able to cut a circular groove a few mm deep. This was then enough to keep the bit steady when I started drilling.
3) Pressure. I had to use a lot less pressure than I thought. Initially the drill was shaking a lot and I had to double check that I had turned the hammer action off on my drill. I had indeed turned it off and found that the shaking was because I was pushing too hard.
4) Time. I already knew that it would take time from the advice I had read. It only took a few minutes to get through the concrete block, but it was much slower through the brick. I Actually I took my time, and did the brick in several bursts, allowing the drill to cool down and give my arms a rest. So for me it was several hours to get the hole finished. But even if I had done it all at once I guess it would have taken 15-30 minutes?
5) Danger. Fortunately I didn't have the experience of the bit catching violently on full power. However since I was doing it in phases, I did experience a catch on starting the drill when I hadn't seated the bit correctly. So I am very glad than I never experienced a full power catch. And I am glad that I heeded the advice not to drill from the outside on a ladder.
6) Hole size. I guess its fairly obvious, but unlike with wood, plastic etc, the size of a big hole in masonry, especially when it has taken a lot of time to drill, is bigger than the drill bit used. I had to choose between 65mm and 78mm bits, and chose 78mm because 65mm was just a tad too small for my need. However in reality the 65mm bit might have been OK. (Maybe experts can make the hole the same size as the bit).
7) Diamond vs TCT. After reading up on the subject I decided to pay the extra for the diamond bit. Since I have never used a TCT bit I can't compare, but looking back on the effort needed with a diamond bit, I am confident that I made the right choice in paying the extra money, even though I may never use the bit again.

 

[xr4x4]

I've only found it catches when you don't knock out the cut bits of block as you go through.

I always knock the bit out regularly, less friction.

 

[Norcon]

I always core witout the center bit. Starting off just hold it between your boots.
If against a wall then get the boots up against the wall too.
Save any faffing about losing the bit down the cavity or the hire out guy moaning when you don't bring it back.

 

[Spark123]

I use the centre bit just to get it going, far enough so the core drill has started and then I take it out.

 

[xr4x4]

I use the centre bit just to get it going, far enough so the core drill has started and then I take it out.

Ditto