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Drilling a Drainage Hole in a Plant Pot

We divided an ancient Snake (a.k.a. Mother-In-Law’s Tongue) Plant and discovered the pot had no drainage hole, which is not to be tolerated.

It turns out that an ordinary carbide glass drill works just fine on glazed clay pots. Use a low RPM and very slow feed, flood the scene with water, and drill from the other side after the point breaks through.

Glass drill for plant pot hole

Glass drill for plant pot hole

The glaze inside the pot already had a flaw that let the water into the clay, from whence it seeped out through the unglazed lower rim. I suppose saturating the clay can’t possibly be good, but I’ve done this to many glazed pots over the years and none of them have ever complained, so it’s all good.

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  1. #1 by peter on 2011-07-18 - 12:47

    A few weeks ago I tried something I never had done before, but had heard about: drilling through glass. To my own surprise, it went pretty well. The glass was about 4 mm thick and the hole I drilled was 4 mm too. Using ordinary HSS drills it went pretty well. Took about 10 minutes (I took my time), but I ended up with a nice hole (and a blunt drill, what is to be expected, as glass is pretty hard – why they use carbide for drilling glass). I was very surprized it went so easy.

    • #2 by smellsofbikes on 2011-07-18 - 14:15

      I’ve spent a bunch of time drilling/cutting glass. One thing that works pretty well is to go to an automotive parts store and buy valve grinding compound, which is a grease filled with abrasive. It costs like $4. Then you can put a piece of tubing in your drillpress, smear some grinding compound on the glass, and use the tubing to cut through the glass. It works somewhat better if you file a couple notches in the tubing end, just small ones, to move the grinding compound around. If you need glass rounds it’s convenient, and it also requires less material removal than a full-size drill. Same thing works with cutting through inconvenient tubing, when you can’t just score and snap it: use an old hacksaw with lots of grinding compound. It’s very slow but it’s reliable.

      • #3 by Ed on 2011-07-18 - 15:36

        It’s very slow

        And how!

        I’ve done that on rare occasions and always wound up with a tired arm from pecking away at the glass in the drill press. I used glass grinding grit in oil and probably made the same mistake I always make with sandpaper: starting with too fine a grit.

        Makes perfect holes, though, which is the point.

        Drilling a clay pot with that carbide bit took maybe three minutes, tops, including wiping the muck off the pot.

        Glass drilling would be a good CNC application, if there was some way to feed back the Z position at the bottom of the hole to avoid smashing the plate. Maybe a torque sensor? Sounds like Yet Another Project… [grin]

    • #4 by Ed on 2011-07-18 - 15:22

      ordinary HSS drills

      I would never have thought of that, but it sounds reasonable: the chisel point chips the glass and the rest of the cutting edge sweeps the rubble off the top. I’ll keep that in mind for a drilling a specific hole size that doesn’t match my carbide glass drills, because I have a bunch of dull / chipped / scrap HSS twist drills waiting for their next life.

      Quite some time ago, a friend asked how to drill a frozen brake fluid vent fitting out of a disk brake assembly. I suggested a carbide masonry bit, with the caveat that it’d be scrap by the time he was done. We were both pleased: it worked well and the cost of the drill was much smaller than the cost of new brake hardware. Sometimes you must sacrifice the tool in the course of the job…

  2. #5 by peter on 2011-07-18 - 12:48

    *which* is to be expected….

    Argh. Sometimes my Dutch roots still show themselves :-).

    • #6 by Ed on 2011-07-18 - 15:28

      You could teach English writing to any high school class around here: you’d do better than the teachers already in place!