Hackaday Links: December 11, 2011

Drilling square holes

We’re still a bit baffled by the physics of this, but apparently it’s possible to drill a square hole with a round bit. This video shows square holes being milled using a cutter which is offset from the center of the bit. [Thanks Jordan]

LED Motorcycle headlight driven by mains

[William] found a way to use a big capacitor and bridge rectifier to run this H4 LED headlight bulb in a mains sconce lamp.

Electronic slide whistle

Here’s an electronic instrument that [Dorian] made. It uses a linear potentiometer and a button and works much like a slide whistle would.

Robot rocks out to Daft Punk

[Adrian] didn’t just make a robot arm out of CD cases and a mints tin. He built the arm, then made a music video featuring it.

More light-pipe sensor experiments

[Uwe] has been working on an input sensor using a flexible light tube. It is a similar idea to these optical flex sensors, but [Uwe] tried several variations like filling the tube with alcohol.


  1. bsom says:

  2. The square drill bit is based on the shape of the Reuleaux Triangle.
    Near the end of the video linked to my name you can see how it works. Because the triangle does not have a fixed center of rotation it wobbles around within a holder, which leads to the awful clunking sound you hear in the video.

  3. Reg says:

    The details of square hole drilling are in Alex Weygers’ “The Complete Modern Blacksmith”

  4. Zee says:

    Here’s a russian how-to video that shows us how square holes are drilled: http://www.youtube.com/watch?v=L5AzbDJ7KYI&feature=related

  5. Dax says:

    “The reactance of the cap means it will drop the voltage down but not dissipate much power as the current will be out of phase with the voltage. Hence the drop is efficient (i.e. no heat). ”

    It’s true that it won’t create heat at the point of consumption, but a large capacitor like that will create a parasitic current that will cause your pole transformer to heat up. While the power to the load is indeed VxI, the transmission losses still follow RI^2

    Large amounts of parasitic current may also trip breakers even though it doesn’t transmit any power down the wire.

  6. Fallen says:

    How much ripple current is that cap seeing?
    We did a project that took 5Vpp and stepped it up to 8VDC, and used a capacitor multiplier. Not quite what he’s doing. But anyways with a 40 ohm load we had on the order of 100s of mA flowing through the cap. It was only rated for 1.4A. Anyways with 60 times the voltage, I can imagine there could be an issue with the amount of current that cap is passing. Combined with the ESR of electrolytics being pretty high…it may fail. And I don’t see any fuses/protection.
    Might want to re-think that one. I got a 120 to 12VDC converter for halogens bulbs at about $6 at the local home depot.

  7. Wouter says:

    The animation of bsom reminds me of how a works.

  8. qwerty says:

    When the light is turned on, the cap is initially discharged (ie it’s a short circuit wrt the current) therefore the leds will get a 120 V spike. If they don’t die immediately is because they already have resistors inside, but they’re calculated for a 12V supply, so they won’t last long.

  9. biozz says:

    you CAN NOT drill sq … holy crap he just drilled a square hole O.o

    im honestly impressed … tho your mill better be mounted VERY securely

  10. biozz says:

    oh may i add using mains to light an LED is nothing new

    we used LEDs and 100k ohm resistors as indicators for blown fuses

    place a 100ohm resistor with an LED and a diode or just 2 LEDs … like

    they can take the voltage just fine

  11. Evan says:

    Another animation of the square hole drilling:

  12. Dr. S says:

    Re: square holes, this wouldn’t be a surprise if you remembered playing with Spirograph. Did you know that there’s a direct correlation between the decline in Spirograph and the rise in gang activity?

  13. macona says:

    Drilling square holes is nothing new. Watts Brothers Tool Works has been making these chucks for years.


  14. Hirudinea says:

    Electric Slide Whistle, for v.2 he should buy a cheap trombone and build this into is, they have electric guitars, don’t that.

    Drilling Square Hole, no mater how many people try to explain it all I have to say is, “Drill square holes, WFT!?!?”

    • biozz says:

      i agree it goes agienst everything your taught about logic XD

    • Michael Chen says:

      “Drill square holes, WFT!?!?” ;

      Upgrade it to

      “Drilling square holes with a triangular bit, WFT!?!?”

    • Dax says:

      But it’s not really really drilling a square hole. Just something that approaches a square.

      The mechanism itself is kinda like a scotch yoke, but in two dimensions instead of one. If you can imagine a slot being cut by a pin in a slot guide, you can imagine a mechanism that does the same for two axis at a same time, drawing a square-sort-of.

  15. damox says:

    Drilling square holes from circles using a triangle!


  16. firestorm_v1 says:

    I’m sure there’s a Minecraft joke to be made here somewhere. :P

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