core drill guide bits

[Fred]

Thanks. My (limited) experience has been with TCT cores, so that was really the question I was asking: is the dust from a diamond core really much worse than from a TCT one? I thought the dust would be the same because they are both cores rotating at the same speed through the same brick, but it seems I am wrong to think that. Thanks for putting the record straight. Too late now, I've ordered a 107mm diamond core to try. Perhaps I should have saved my money and stuck with the 110mm TCT one I already have!

I have angle grinded and wall chased with diamond discs before, so I certainly know about the dust! One day I intend to buy a Dyson DC04 or

07 from ebay to use as a dust extractor. I'm still not sure whether it's worth paying the extra for the 07 over the 04?

Since diamond discs in grinders do wear down over time, is the same true of diamond cores? OTOH I suppose TCT cores wear too, and faster, so I guess there's no getting away from having to replace them.

Thanks.

[John Rumm]

The SDS is probably a better bet. One thing to watch is that you don't overheat a DIY class drill - it needs lots of airflow through it, so keeping the revs up is important.

Well, as I said there are valid reasons for having an ordinary drill. SDS is only really a benefit for masonry - for most other tasks its actually less ideal than a more basic drill. For me the combination of

18V combi and SDS covers most drilling tasks I undertake, but I could imagine cases where using a mains drill would be preferable if one was in a production environment working with it all day etc.

[John Rumm]

You can (if you don't mind creating all the dust inside!) - generally if you take it easy on exit you usually get a clean hole.

It would suggest a weak or already broken brick...

Pilot drill through and drilling from both sides will guarantee clean holes, although at the slight risk of a minor mis-alignment or bend in the hole.

[John Rumm]

Most of the dust from core drilling is better contained than with a AG. You get some fine floating stuff toward the front of the hole, but once in the wall this is controlled reasonably well. Personally I use diamond over TCT. I usually gaffer tape a dustbin bag under and around the drill site to catch the bulk of the stuff that falls out. Having someone else on vacuum duty when starting a hole helps contain the initial blast of fine stuff.

[John Rumm]

Yup, they wear - the "teeth" get shorter until they eiter end up flush with the rim or (more likely) stopp cutting some time before that.

[John Rumm]

400mm long SDS bits in 16, 20, 22, and 25 are commonly available. Larger can be had, but they get a bit pricey and work better in higher impact energy SDS drills (the 4 - 5kg class pro models)

Assuming you will do copper pipe sizes with a normal bit, then a 38 and a 52mm core set will cover most other eventualities. At worst you end up with 5mm of gap around a pipe, which is ideal for injecting some sealant into.

[John Rumm]

A search for "diamond core" brought them all up for me first time. Remeber not to just look at the top five matches - but expand the Core Drill Bits section out below.

I have not seen them do a core drill, although they do some SDS ones.

Stick the core in a wood working vice (wrapped in a cloth) and use the flats on the arbour then...

[Fred]

[...]

I did the drilling all from the inside because drilling from the outside would have involved working off a ladder and I wasn't keen on being up a ladder if the clutch failed and the core jammed. It seems that either way has its disadvantages: drilling from both sides might have slight misalignment and drilling outside in may damage the bricks.

[Fred]

How many revs do you need? I thought you had to go slow, especially with large cores. Would the drill set to its lowest speed generate enough airflow, or would you suggest removing the core from the wall and spinning it faster in the air to cool it every now and again? Thanks.

[Fred]

I was about to buy the Bluespot cores from Amazon when you gave me that link. Thank you very much. I think I ordered the last 107mm core. They also had a 152mm core for 6" ducting. I bet that is interesting to use!

I see what you meant about the guide bits: the long guide bit in the diamond core and the short bit in the TCT core both protrude by about the same amount once inserted. They supplied a bluespot bit BTW.

I'm not sure about all this talk about using drifts to remove the guide bits as my experience in both the TCT and diamond core is that the bit falls out the arbor too easily: I hear a metallic ringing and remove the core from the wall to find the guide is stuck in the wall, detached from the arbor.

I couldn't get the diamond core to get started in my [brick] wall. I think the guide bit issue didn't help, so I reused my TCT core to cut an inch or two into the wall and then carried on with the diamond core from there.

[about tct core and arbor sticking]

I'm not sure my vice would open wide enough to take a 107mm core. I did manage to free it using a 22mm spanner on the arbor and an earth spike through the holes in core to hold it in place. The spike got bent in the process though.

[Fred]

I did find that the dust was very soft as described earlier in the thread but you are quite right, it was nothing like an angle grinder. I could always see the whole of the room I was in ;) Of course, I've only drilled the one hole but I would say to anyone in my position not to worry about the dust, it really wasn't that bad but: in my limited experience, YMMV, etc.

Thanks for all your replies John, they've been very helpful.

[js.b1]

The 152mm bits are heavy and quite difficult to get started, patience required.

Dust is very much contained to the area being drilled - some "smoke" wanders, but nothing like with an angle grinder. #1 do not obscure the drill's fan outlet in such a way as to direct a blast of air into the dust stream, generally the air stream is too hot but if it does happen you will soon know when you look around after drilling :-) #2 the 152mm bits have side slots obviously some inches from the centre which throws dust out radially, screwing a height cut-down bucket with a hole in the bottom to the wall with a vacuum duct taped to the bottom might prove useful.

Wonderful tools, the small 22x350mm & 28x350mm are great for round conduit through cavity walls.

[John Rumm]

For the typical core sizes (i.e. up to 150mm) they usually recommend 900

- 1300 rpm. That's usually max speed on a SDS, but some single speed drills can be more like 2400. A drill with a low speed range on the gearbox may well be about right though.

Basically make sure you are not covering any ventilation slots as you drill. Keep you nose open for anything smelling like melting plastic etc hot. Try not to make the drill labour such that its speed is slowed significantly. If you need to cool a drill quickly, then a but of running in free space will do so faster than turning if off.

[John Rumm]

Not done a 6" personally - but I expect 'kin heavy would be the word. As JS said - I can well imaging getting one started is a pig as well.

Yup, if following a pre drilled pilot hole they do tend to work loose IME. Having said that, you only need it for the first few mm - the core will stay on centre once its edge is in the wall.

I tend to put a bit of wood on the end of the bit and clomp it home with a hammer. That usually sets it in there for long enough.

The trick is to get it spinning and then offer it to the wall gently...

A mechanics vice would have to be quite large, but wood working ones usually open that wide. You could just stick a bit of plate in a vice and engage the lugs over it - however that would risk breaking a lug!

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Fred saying something like:

Or fallen down the cavity.

[Fred]

I had my 107mm core on a Screwfix Titan sds drill. It has a speed setting from 1 to 6, so I had it set on number one. Perhaps this was too slow for adequate cooling? It seems that some Titan drills mention a clutch in their description and others do not. My model was one that did advertise a clutch and it appears to work! Once or twice the core stopped turning and the drill "buzzed" but it didn't kick and my wrists are intact.

[Fred]

Is that the largest core in normal use? I can't think of a reason to go wider domestically but does ducting in commercial situations require bigger holes?

Getting the 107 core started was a pig but perhaps that was because of my inexperience? As I said, I had to start the cut with the tct and once there was a slight circle scribed into the brick to guide the diamond core it worked well. Without the slight groove to guide the diamond core, it just bounced all over the place. I hope with practice my technique will improve. Using tct to start a diamond core rather defeats the point of buying diamond over tct!

I tapped it against the wall to get it stuck but it soon came loose again ;)

Hopefully I will improve with experience then. I resorted to the TCT because I was cutting from outside and didn't want to risk the diamond core dancing all over the brick face and ruining my wall.

I think I bought the 4" vice rather than the 6" to save money. IIRC I paid for the Irwin which was twice the price. Perhaps I should have bought a bigger version in a cheaper brand for half the price?

Thanks.

[Fred]

What a useful thread. I always thought I couldn't use diamond because I didn't have a special drill and now I know better. Why do they bother painting diamond cores since the paint is rubbed off as soon as they are used?

On the subject of using drill bits for smaller "copper pipe" sizes, can you get short 22+ mm bits? All the ones I have seen are 600mm. Great if you have to go through a cavity wall but impossible if you are in a confined space. At the other extreme, I wanted a long 8mm bit but could only find them in short lengths. B&Q did have a wide selection of lengths made by Bosch but at £60 each, I walked by.

Thanks.

[Fred]

One last question: I know about the rules regarding notching joists, and that you are only supposed to chase 1/3rd the depth of a wall but are there any rules about punching holes all the way through a wall, e.g. by using a core? I can imagine that kitchens may require a number of holes to pass ducting from a cooker hood and other extractor fans, plus a boiler flue. Is there a limit how many of these you can have in one wall or how far apart they should be? I am guessing smaller holes, e.g. 40mm waste, are less significant?

Thanks again.

[Tim Watts]

On Thu, 10 Jun 2010 20:43:25 +0100, Fred wibbled:

Re large holes - not usually a problem unless you stuck several next to each other. The circular hole transmits the stresses quite nicely anyway.

40mm waste - absolutely a non problem unless you are planning to put 1/2 dozen in a tightly spaced row :) Even then, if they were at 50% density, the wall would probably survive.