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First-time driller here, so please bear with me! :)

I was trying to afix a shelf in the wall, and started to drill the holes for its mounting brackets. The wall is reinforced concrete, and I was using a standard 6mm masonry drill bit attached to a hammer-function-enabled machine. I stumbled upon several problems:

1) The drill bit at some point became fixed in the wall and was no longer spinning - only the machine's circular grip was spinning around it. I tightened the grip and continued, but this happened several times.

2) The drill would still not advance, so I ended up using a 4mm bit to go in first, and then followed up with the 6mm one that I needed.

3) Although I used a wall detector to check for pipes/wires before drilling, I was very nervous since the detector seemed to very unreliably beep over the same locations, perhaps because of the metalic reinforcing bars in the concrete. In the absence of (useful) building plans, is there any other way to prevent drilling into pipes or wires?

4) After finishing drilling with the 6mm bit, my wall plug (anchor) did not fit the hole, even when (gently) hammered in; and drilling some more (by applying pressure towards the sides of the hole) to make it a bit wider also did not suffice. Both of these strategies together (hammer+enlarging the hole with same drill bit) had previously worked when I drilled into a softer wall (not sure if that was cellular concrete or drywall)!

5) I reckoned that given the hardness of concrete, I maybe just need to use the next-larger drill bit size, 7mm, to fit the 6mm plug; but my set does not include one (the next up is 8mm), and none of the sets I can see on Amazon include 7mm (for concrete or masonry) either, only for wood!

Sorry for the long and rather incoherent question, but I hope that someone can advise on how to best proceed despite my beginner mistakes!

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    So the current status is you have a hole drilled with a 6mm bit and then slightly enlarged, and an anchor that still does not go into the hole? What size hole is the anchor designed for? Can you add a link to the anchor so we can see what type it is?
    – fixer1234
    May 20, 2018 at 23:26
  • That's correct. The anchor is designed for 6mm holes/bits: conrad.com/ce/en/product/1490169/…
    – z8080
    May 21, 2018 at 6:49
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    Did you verify that the hole is at least 30mm deep? How far in does the anchor go?
    – fixer1234
    May 21, 2018 at 7:05
  • I checked the depth with the drill bit itself - seems to be around 50mm. The anchor only goes a few mm in - to go depper, I'd have to really hammer it in - which I've tried, and broken one anchor; that's why I reckoned that I simply need to use the next-up drill bit (7mm). I'm just surprised that most sets skip this size, going from 6 right next to 8mm
    – z8080
    May 21, 2018 at 7:53
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    The anchors are tapered, so they should go a good way in easily, and then the rest of the way with light tapping with a hammer. Try measuring the diameter in a few spots. There are ridges for friction, but the main body should be no more than 6mm. If they are larger than 6mm, maybe the package was mislabeled.
    – fixer1234
    May 21, 2018 at 8:06

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Measure the drill bit. Measure the wall plug. Adjust one or the other until they are the same size. If you drill a 6mm hole a 6mm plug will go into it, it's just physics! Make sure you blow out any dust in the hole and as mentioned above, make sure the hole is slightly deeper than your fastener length.

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Try starting with a smaller bit, and even an intermediate size before the final size . Cool and rinse the bit in water occasionally. Drill bits cut only with the end, not the sides ( I know, I use them to wide holes also. but when I worked in a bit factory ," flutes don't cut" was "drilled" into my head.) If you hit steel rebar , I would move to a different spot. My Black and Decker chuck slipped ; I got a Makita and it doesn't slip.

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