Solar Tracking CNC Wood Burning Experiment


A Guy In Town
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Okay, people say I am crazy.  I accept that.   I like to try new things, and experiment a lot.

So I have a few of the PlasmaCam CNC tables.  I have a 4x4 that is my experimental table, which is modified as needed.  I have a 5x10 plasma table for metal art.  I have lots of spare parts, etc.

Remember when you burned wood with a magnifying glass as a child?  You would use the sun as the light source, and try to control the convex lens to burn dark lines or lighter brown areas into wood as you moved the lens over the surface, staring into that bring white hot spot until you are blind.  Most of us did not stick with it, because it is difficult to maintain a steady control of the lens over a long period of time.

Well, I decided that my CNC table is the answer.  I bought a motorized solar tracker from Amazon.  It is normally used to rotate a series of solar panels so that they always face the sun as it passes overhead.  I am going to mount the rails and gantry from a PlasmaCam 4x4 table onto the tracker in place of the solar panels.  A magnifying glass lens will be mounted in place of the plasma torch.

Using the software to control the carriage, I should be able to burn some detailed and intricate designs into birch plywood.  The computer can control the speed and direction of the lens, and the Z axis will raise and lower the lens to either bring the sun's rays into sharp focus, or perhaps a softer, wider spot to create various shades of brown.  With computer accuracy, I should be able to control the lens better than I ever could by hand.

This is just an experiment, but one that I truly believe will work well.  My initial burns will be straight lines, set at different speeds and different heights over the wood, adjusted in thousandths of an inch!  Once I know what setting produces what result, I will make some basic drawings and let the cnc machine burn the images into the wood.  I am hoping to create something new and different, something that no one else is doing.

It will take me a few months to pull this project together.  Soo many things to do.  So little time.

Joe

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The light from a magnifying glass is a focused CONE of light.  So the tip is the hottest, and as you move up the cone, the spot becomes wider and cooler, with the same amount of light disbursed over a larger area.  I think I will be able to create gradients of various shades of brown and tan that a laser cannot match.  This is all possible by hand, IF your hand is steady enough, and you can stare at the hot spot for a few hours!

With the computer, and knowing the speed and the height of te lens over the material to produce any given results, it is just a matter of drawing the design and assigning the speed and height of each path.

This is all conjecture at this point.  i do not think ANYONE has tried this.  We will see soon enough.

 

Joe

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OK, I see the potential, but it still seems shaky to depend on sunlight as the "power source". I live in TN, and even this far South, there are a lot of sunny days per year where the sun's attitude in the sky means a very large lens is necessary to focus enough energy to scorch wood in an acceptible amount of time. And forget about cloudy days. 

You mention that your cnc tables are plasma cutters, maybe you would get more control by using the cutter's energy to drive an arc lamp as the source of light? Following this idea through to a commercial product, an arc light and varifocal lens system might produce exactly the effect you describe, and be carried by the cnc gantry. And work at night!:D

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This isn't about artificial light, or lasers, or plasma torches.  It is about burning wood with a magnifying glass as I did when I was a child, but with computer accuracy.  I have absolutely NO IDEA what the results of the tests will be.  Maybe I will fail.  It would not be the first time.  My failures do not bother me.  It is those the things that I did not TRY when I was younger, that keep me awake at night.

Joe

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My table has six inches of Z so there is a lot of vertical movement for the lens.  I will figure out what height above the material the lens needs to be, in order to get the hottest, sharpest focal point,  and mount the lens so that when the carriage backing plate is fully DOWN it will achieve that hot spot.  Raising the lens slightly SHOULD give me varying degrees of lines, from dark brown and a little wider, to light tan and very wide.  Remember that burning wood is about BTUs, so any specific height will give varying results, depending on how fast the lens moves over the material.  I am also certain that the same settings will give different results on different material.  Burning oak or walnut will not react to the programming in the same way that birch plywood or white pine might.  

Understand that at the moment, I know absolutely NOTHING about how this will turn out!  The first tests will be straight lines at various heights and speeds, and then "fills" filling in squares or circles with the height and speed determined by the first tests.  Then I will try to program gradients!  Then other patterns.  I am not expecting to produce a museum quality piece on my first day.  I would be proud at some point, to have a nice art piece hanging in City Hall though. B)

 

Joe 

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When I set up my first Samson 510 cnc plasma table (PlasmaCam's "Big Brother") I spent two years using a ROUTER on the table because I did not have ventilation for the plasma smoke and dust.  I got really good at carving things, and in fact, I have a lot MORE FUN using a router on the Samson table than when I use the plasma cutter.  i can do a lot more!

 

Joe

 

 

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The gantry and carriage move with 36 pounds of force. They are driven by gear racks, not belts.  so I cannot imagine that the machine would have an issue with moving either the gantry or carriage in either direction on a tilted plane.  The machine surface will not go full vertical. It is just going to be tilted toward the sun and maintain that position with the sun remaining essentially directly overhead all day long.  As for accuracy, well ... when you use a magnifying glass to burn wood with the sun, you will notice that the spot does not move when the lens is rotated on a handle in your hand.  the spot remains in place, and only the shape of the spot changes, when the lens is not bisecting the sun's rays shining down onto the material.  

I only wish I had an assistant.  There is SO MUCH work to do here, and I am only one man.  Right now, I have te task of producing a dozen large Halloween tombstones, so the solar project will have to wait a while.

Joe

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