I need to drill one 115mm/4.5" hole – ish, it just needs to provide reasonable clearance for 4" triple wall drain pipe) – (or maybe two if I blow it the first time  ) in a 1 3/4" thick concrete paver. I'm thinking that I would use my Milwaukee M18 SDS-plus hammer drill, but I'm striking out all over the place looking for a bit. I was hoping to find a semi-serviceable "one-hole wonder" on Amazon (I don't see too many more downspouts going through pavers in my future), I'd be willing to buy a Bosch Speedcore (or the like), but my Google foo just isn't working and I'm either coming up empty handed or finding $500+ bits that look like they can cut an 8" core…

So, I'm looking for suggestions. A source for a 4.5" SDS core bit, other ideas for bits (I stumbled on claims that the Sypder carbide bits will cut brick, but haven't found an SDS mandrel – would a conventional mandrel work in an SDS chuck adapter?), or tricks for cutting a relatively clean round hole in concrete pavers.

If the paver is not too thick you could use one of these with plenty of water.

But if it's thick you will need this.

These are only 4" but that may be enough.

There's a few ways to go about this.  As you've mentioned, a core drill will perform well, but it's probably unjustifiably expensive.

Likewise, as Alex suggested the Bosch Speedcore will perform the task well, if a trifle expensively.  The huge advantage of the Speedcore is that it uses a pilot bit for guidance.  Once the pilot punches through the other side, if you turn the paver over to finish the hole you'll minimise breakout.  Your Milwaukee cordless SDS should be darn near perfect for this type of bit.

Those diamond holesaws mentioned seem to be pilotless, & you'd need extremely accurate measurement on both sides of the paver to core through the whole paver's thickness from both sides effectively "blind".  In addition, these tools' shanks are a standard 3/8 hex or round, & won't work well even with an accessory SDS+ adapter chuck, tending to slip in the chuck (if round) due the high torque required to drive such a large diameter.

You shouldn't be using any impact at all with gritted holesaws.  Meaning that any quality lower-speed high-torque drill will work with these.  I've had good results with a (corded) Bosch GBH 4 (which has interchangeable chucks & drilling/hammering/chipping modes) with large diameter holesaws in a variety of materials.

I also think Alex's suggested "budget" method of multiple holes within the circumference of your required diameter would work, albeit slowly.  You could use any bit that you already have, although smaller diameters will drill faster & minimise breakout on the bottom.  However I wouldn't recommend using a rasp to clean up the circumference.  Concrete is too hard, esp. the high MPa concrere used to make pavers.  I doubt anything less than diamond would abrade this type of high strength, brittle concrete.

Better yet would be a stone grinding disc fitted to a mini-grinder, which will make messy but fairly short work of any imperfections in your hole.  Had to do this myself to "square off" the overlaps of 3 x 300 mm cores through a concrete tilt panel.  Appropriate PPE is a must:  silicates in cement are dangerous.  You'd have to use the grinder from both sides.

A bit of clearance around the hole is advisable when using softer PVC plumbing fittings through hard or abrasive materials to allow for thermal expansion, movement & the possibility of replacement.  Just a few MM would suffice:  say a 4 1/4" hole for a 4" pipe?  A bit more if you have to feed a female flared end through the paver.

If it is just one hole, don't underestimate basic bi-metals.  You can use them on brick and other similar materials. You will destroy it pretty fast, might even take more than one for the hole, but from a price standpoint, a couple of them can still be cheapest option.

If I remember correctly, I drilled a hole through a paver with a 1/4" SDS bit and then used this carbide/diamond grit hole saw on a cordless drill to come in from both sides of the brick. It's rather slow going but it will work, just make sure to use lots of water and flush the swarf from the cut often.

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Was the SDS bit used for anything more than a landmark on the other side? How did you position/stabilize the bit as you started the cut?

I think the preliminary 1/4” hole is to provide for an ordinary non-carbide pilot drill, to guide/position the abrasive hole saw.

Exactly correct Michael... This is a pilot that I use specifically on drywall, bricks, tile or anything that would ruin a normal HSS drill bit. Look closely and you can see the brazed carbide on the tip of the drill.

Not sure what you consider inexpensive but I found a number of 4.5" diamond core bits on Amazon for under $99, many with 5/8-11 thread that will connect to a grinder.

Under $100 is in the range of "tolerable pain" for one hole that I want to look good. I think I found some of those too, but wasn't considering them due to the lack of a pilot bit. Hadn't thought about a grinder either. How do you stabilize the bit to get the cut started (before you have enough of a hole to keep the bit from wandering)?

How do you stabilize the bit to get the cut started (before you have enough of a hole to keep the bit from wandering)?

I have this thing from Bosch to drill with diamond hole saws into tile. For single use you can make one out of scrap wood, the hole doesn't need to be round but can be square, it just needs to trap your hole saw.

Quote from: Bob D. on August 11, 2020, 06:00 PM

Not sure what you consider inexpensive but I found a number of 4.5" diamond core bits on Amazon for under $99, many with 5/8-11 thread that will connect to a grinder.

Under $100 is in the range of "tolerable pain" for one hole that I want to look good. I think I found some of those too, but wasn't considering them due to the lack of a pilot bit. Hadn't thought about a grinder either. How do you stabilize the bit to get the cut started (before you have enough of a hole to keep the bit from wandering)?

I used a piece of 3/4 plywood from the scrap bin and cut a hole in it to the OD of the core bit. Then I anchored that to the surface I needed to bore the hole in with the core bit. In my case it was some concrete pavers 18x18x2" I clamped the plywood in position using two quick grip clamps with the rubber pads. They don't slip and take a firm grip on the concrete. Worked out great. The ply guided the bit until it got a cut started and also help to retain some water to cool the bit. Once I got the cut well established at about 1/2 depth I removed the plywood. I also used a RIDGID cordless 4.5" grinder to make the cut, but a corded would work just be careful with the water and use a GFCI on the tool.

I would definitely nibble with a hammer drill as Alex suggested.  I did this through brick for my DC exhaust and clothes dryer exhaust.  Doesn't take long but needs something to hide the ugly hole edges.  It will probably fall out if you make holes all the way around as close together as possible.  If not, a could taps should finish the hole.