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Core Drills Question

Discussion in 'Plumbing Tools' started by Tired, Nov 26, 2016.

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  1. Tired

    Tired New Member

    I'm a builder rather than plumber so hadn't used core drills until now. I've bought a Dewalt D21570K which was recommended by a plumber. I went on to buy a set of Dart drill bits. Both items weren't bottom of the range but not far off. I only needed the drill to make three holes hence the desire to not pay much more.

    I'm drilling through a concrete foundation which has been down for about a year. The drill seems to be struggling in the hole it's made rather than with the drilling of it. I'm past the drill bit now which is when my progress nose dived. I thought maybe it was causing a vacuum so I pilot drilled all the way through. This hasn't helped! The concrete may still be a bit wet although it is near the top of the strip about 10cm below the bottom block.

    I've read a few things online about slots in the bit causing vibration and clogging but this doesn't seem to be my problem. Is there something I can put on the bit to lube it in the hole? Is it likely I need a better bit? I'd appreciate any thoughts or pointers.
  2. Tired

    Tired New Member

    I perhaps should have mentioned that the Dart drill bits are Diamond and the Dewalt is a core drill. The hole I'm trying to drill is 65mm.
  3. kris

    kris Trusted Plumber GSR

    In my experience coring hundreds of holes the drill must be 100% level as slightly off and the core bit starts to jam against the outer wall, I'm not trying to teach a granny how to suck eggs lol ( pardon my phrase usage ) but defo this causes major friction , also if I haven't already put a pilot hole in then I usually take the centre bit out once I've got a start,
    Also some core bits the diamond teeth are slightly wider than the barrel of the core giving u than millimetre of clearance but wet concrete can always be problematic,
  4. gmartine

    gmartine GSR

    If you're at the depth of the core drill and you want to go deeper have emptied the core of it's contents?

    I'd also proceed without the pilot drill.
  5. Tired

    Tired New Member

    Admittedly I'm on my knees in a trench trying to get the core drill in perfectly straight, therefore I'm sure the angle is adding to the issues I'm having. With reference to the second comment above, I'd love to have contents to empty from the core. I'll definitely try without the pilot bit. Is there any guidance on whether I need a different bit to compare to? I live in rural France and the French don't have the same system of core drill so I'm slightly stuck with regard to what I can order online as it has to be from UK. Makita do a box of drill bits with mostly positive reviews. A plumber said he uses Erbauer.....I wouldn't touch the tools but perhaps the core drill bits are okay? Is there a bit that works well in potentially moist concrete? Appreciate the advice.
  6. snowhead

    snowhead Well-Known Member

    Have you got a brick wall you can try the core in so you can see how it performs?

    1st core and into concrete is a steep learning curve.
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  7. GQuigley67

    GQuigley67 Trusted Plumber GSR

    I would also like to add that particular core gun sucks, mine lasted a year, had to hire the makita to finish a job.
  8. JCplumb

    JCplumb Plumber

    I've done a 110mm core with a Dewalt SDS drill, took about half an hour in all I was curious to see if I could, how thick is concrete? Mine was 300mm.
    As mentioned above, make sure the drill is level and don't try to force it, just let the core bit do its thing with a small amount of pressure, take it out every minute or so and clean the bit up, when you can - knock out any of the cylinder to give one less surface for the bit to catch on.
    I know how tempting it is to push hard, especially as you're in a trench.
    Slowly slowly catchy monkey :D
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  9. Billy Bob Bob

    Billy Bob Bob Guest

    Seen the dewalt version you have and TBH it looks like a cheap percussion toy,i use a DDM3 but this is not a cheap drill,as Kris pointed out ,needs to be perfectly strait
  10. joni os

    joni os Plumber

    Coring wet bricks or concrete can be challenging, as often a slurry forms and clogs the diamond matrix. This doesn't happen with wet drilling as the water carries the slurry away.
    To sharpen the core bit, (expose the diamonds). Drill into dry high strength concrete, like a pressed paving slab with granite aggregate. With pilot hole through footing you could try introducing flowing water from far side to clear slurry, but given electrics and possibility of flooding trench this option appears limited. Alternate one minute coring with 10 secs sharpening will get you through.
    • Like Like x 1
  11. REDSAW

    REDSAW Guest

    agree diamonds clogging
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