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Thread: CNC Laser - Getting Close

  1. #1
    Join Date
    Aug 2007
    Reno NV

    CNC Laser - Getting Close

    So, As I've mentioned in some other threads, I think I'm starting to get close to getting the laser etching thing working.

    This is an example of an image that I'm thinking is not really all that well suited to it. The more I play with this, the more I realize that there are some variables that need to be thought about.

    1) The image and the contrast
    2) The amps going into the laser
    3) The max value and min value you need to set in the software that creates the gcode
    4) The material you are burning it on. Every piece of wood seems to react differently.
    5) The distance from the diode to the workpiece
    5) Make sure you focus the beam before you even think about starting a test.

    But, I think I'm getting close.

    I think I need to find a better 'target' for burning. I've tried cherry ply, this is just some cheap birch.

    Time or more experimentation. You should see the amount of scrap I've burnt through so far.

    (ignore the line going from left to right, that's because I reused a sample piece)

    Click image for larger version. 

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    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
    "A door is what a dog is perpetually on the wrong side of" Ogden Nash

  2. #2
    Join Date
    May 2007
    Kansas City, Missouri
    Looks a whole lot better than what I tested on, mine came out completely black. You're absolutely correct about the variables. Wonder if there is some software to take into account some of these and spit out some recommendations?

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  3. #3
    Join Date
    Dec 2006
    Yorktown, Virginia
    It seems more art than science. I does look like you are zeroing in though.

  4. #4
    Join Date
    Aug 2007
    Reno NV
    I should also mention that getting here involved

    1. Laser version of GRBL
      Finding a version of Grbl that supported a 'laser spindle' mode.
      The big deal is that when you change the spindle speed, you do not want the x or y to pause. But since they assume that most spindles use rotating bits and not photons, there is a micro pause. There is a parameter in the config.h file you need to change, and then you can use the arduino IDE to upload the custom grbl firmware to the arduino.
      Works like a treat.
    2. Efficient Gcode Sending Program
      I had been using the Universal Gcode Sender in Ubuntu linux. The problem is it seemed to have issues with the buffer. With these kinds of pictures, you have a LOT of gcode commands to send, and the buffering can sometimes cause pauses to happen, which of course, with the laser turned on would cause it to burn deeper than you want. So I upgraded my shop PC and installed Windows 7. The Win 7 version of Universal Gcode Sender worked much better I used a few different gcode sending programs and this is the only one that kept the buffer filled and running 'mostly' smoothly. I did find that I had to make sure I closed it out and restarted it after each send to make sure it was fresh.
    3. Appropriate Sample GCODE
      I used a perl script to generate some gcode that would run burn some sample boxes at the same mm pitch and speed as what I would use with the actual picture burning so I could estimate what I should use for the max and min spindle values
    4. Find an appropriate image and edit it to black and white and set the contrast and brightness correctly. I'm still working through this issue.

    I had spent a lot of time trying to get this to work before I got those 4 key parts done. Now I feel like I'm zeroing in on this, but there are still a lot of variables other than those.

    Still, Kind of fun!
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
    "A door is what a dog is perpetually on the wrong side of" Ogden Nash

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