CNC Zen Garden

Four strings drag an aluminum slug through a sandbox



Meet the second version of [David’s] sand manicuring CNC machine. We saw version one about six months ago which he built for a science museum in Canada. This offering is much the same, except for the controller. The initial version demanded a full-blow computer to drive it but now that has been swapped out in favor of a Beaglebone Black.

The software has no feedback on the position of the plotter, which is an aluminum slug that [David] machined at Calgary Protospace. It needs to be in a specific position when the machine starts out, and from there patterns are traced by calculating how much spooling or unspooling of the four strings will move the slug.

There’s a bunch of other really neat art installations and projects on [David’s] webpage, it’s worth clicking through!

31 thoughts on “CNC Zen Garden

    1. Its meant as something artistic or decorative, like a fish tank or statue. Most fish tanks are about as useful as shaving with shit too but hey, people still own them and sink thousands of dollars into them. I could make the argument that since this required at least some skill, and its nice to look at.

  1. While I remember admiring this build 6 months ago, I don’t think it deserved a second post just because he swapped a computer for a beaglebone black.

    1. They should have a weekly post similar to the ‘Links’ post on Sundays where they link to an old HaD post and mention whatever updates took place on the old project and then link to the page containing the updates. Hackaday Updates or something.

        1. For a Zen garden, it would need to start out from a “centered” position. As in “With regular chanting, our sense of being centered gets stronger and stronger.” ;-)

      1. No, all it needs is a point in 3d space, and to be told where that point is located WRT machine limits. Most CNC machines (especially the big ones that can hurt themselves if confused) use a set to limit switches and/or scales to set up the machine limits, but also still need to be told where a reference point on the workpiece is, and an accurate idea of the size/shape of the stock WRT machine limits so as to avoid collisions.

        Obviously, this isn’t precision machining, so machine limits and some idea of the height of the sand surface would be the only requirements.

  2. Cool. An improvement on this might be putting the mechanism underneath the table with a large magnet instead of what you’re using to scrawl, with a steel ball resting on the sand.

  3. What it needs is a way to have constant tension on all four lines so it could be used to retrofit old pattern following cutting torch arms with gas or plasma torches.

    How those work is they have a gearmotor with a 1/4″ diameter, knurled, magnetic shaft directly in line with the torch. An arm holds a steel pattern above the table and the magnet rolls around the edge of the pattern.

    The pattern has to be 1/8″ smaller all around than the shape being cut and sharp corners are pretty much impossible. Too tight an inside corner and the magnet will get stuck. Too sharp an outside corner and the magnet can come loose from the pattern. If it does stay stuck it makes a rounded corner as it rolls over the sharp corner on the pattern.

    The mechanism to CNC one of those would be quite simple. Build a frame with a motor at each corner. For the part to move the torch, make a piece with a ball bearing that’s a slip fit over the magnetic shaft then connect cables from that to cable drums on each motor.

    An ideal way to do it would be to have roller fairleads at each corner and single wrap cable drums so there’s no errors from the cables moving up and down or changing drum diameter from the cable wrapping up more than one layer.

    Then you have the calculations (the hard part) to keep balanced tension in four directions and for the non-polygonal maximum movement space of the end of the arm – unless you want to restrict it to the largest quadrilateral that fits within its envelope.

    One more issue would be the free moving “elbow” joint in the middle of the arm. At maximum reach and straight out it might bind a bit before bending when moving back toward the support column. Easy fix for that would be a light spring on one side to ensure it always bends the same way and *will bend* after being pulled straight.

    A three motor system could work – with two motors on the support column side, the third motor straight out from the column and two dead weights and cables to pull towards the outer corners. To move outside a line between one column side motor and the outer motor, all three motors would have to reel out and let the weight pull. Since the tool is a cutting torch there’s no push back from cutting forces.

    Calculations like would be needed for such a system have been done, for eight cables, to move a tool in 3D, and extremely fast. 2D *should* be simpler.

  4. If you take this large scale say with four car winches. you could run this over a massive area. you could make a large section of beach covered with patterns then clam it as a alien “beach circle”


      I love the idea of a portable device-this would be a very cool way to do public art that doesn’t leave behind any objectionable material (yaknow, paint, chalk, etc). You’d need the right surface though.

      This would make an unbelievably cool Burningman project except the event staff is quite serious about “leave no trace”, which includes disrupting the Playa surface, and said surface is actually quite hard.

      1. Burning Man inherently disrupts the playa surface. Just rake it out nicely when you take down the machine. We would all appreciate your art. My main concern would be the people walking on it and messing up the pattern (unless you close it off.)

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