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Laser engraver focusing

Discussion in 'Laser Cutters' started by Brianc, Feb 13, 2019.

  1. Brianc

    Brianc New
    Builder

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    I have finally gotten some time to play with my Acro, somewhat prompted by the wiring video recently posted.

    I have everything moving using the open builds software (very nice) and hoked up the laser tonight. It’s an inexpensive 2.5 watt 450 Ne from AliExpress. Everything seems to work, it turns on and off, but I have no idea how to dial in focus or feed rate.

    Anyone care to offer some guidance?

    Thanks

    Brian
     
  2. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

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    Hi
    Assuming you have it wired for PWM power setting you can turn it on 'very dim' and set the focus (wearing your protective glasses of course, very dim is still dangerous to eyes).

    Once you find the focus distance you can make a height setter out of plastic or wood that lets you quickly set the height above the workpiece. Even commercial laser cutters come with such a spacer for setting cut height (-:

    So to turn the laser on in very dim mode....
    M3 S1 <--- adjust that number up till you get what you need. Max is S1000 if you are using GRBL defaults.
    you may need to give a G1 command fter the m3 to tell GRBL to turn on the laser.
    You should read this, the GRBL laser manual
    M5 to turn it off again.

    Feed rates are a simple matter of experimenting on various materials and making notes. I would use a technique called the binary search. In a binary search, you double or halve your index as a means of getting to your target in less time.

    So, say we have this gcode
    Code:
    G90 G21 G49 G17 F100
    G00 X0 Y0
    M05
    G00 X0.000 Y0.000
    M03 S500
    G01 X30.000 F100
    M05
    G00 Y10.000
    M03 S500
    G01 X0.000 F100
    M05
    G00 Y20.000
    M03 S500
    G01 X30.000 F100
    M05
    G00 Y30.000
    M03 S500
    G01 X0.000 F100
    M05
    G00 Y40.000
    M03 S500
    G01 X30.000 F100
    M05
    G00 X0 Y0 (home)
    M05
    M30
    
    which draws 5 parallel lines.
    M03 S500 sets the laser to half power
    the F100 sets the feedrate and so far they are all the same.
    We want to change the feedrates so that we can see the effect
    Code:
    G90 G21 G49 G17 F100
    G00 X0 Y0
    M05
    G00 X0.000 Y0.000
    M03 S500
    G01 X30.000 F100
    M05
    G00 Y10.000
    M03 S500
    G01 X0.000 F200 ; double the previous one
    M05
    G00 Y20.000
    M03 S500
    G01 X30.000 F400 ; double the previous
    M05
    G00 Y30.000
    M03 S500
    G01 X0.000 F800 ; double again
    M05
    G00 Y40.000
    M03 S500
    G01 X30.000 F1600; double again
    M05
    G00 X0 Y0 (home)
    M05
    M30
    
    So each line is cut twice as fast as the previous one allowing you to quickly see the effect of a range of different speeds.

    We can also keep the feedrate the same and change the laser power in a similar way
    Code:
    G90 G21 G49 G17 F100
    G00 X0 Y0
    M05
    G00 X0.000 Y0.000
    M03 S500
    G01 X30.000 F100 S1000 ; full power, might catch fire!
    M05
    G00 Y10.000
    M03 S500
    G01 X0.000 F100 S500 ; half power
    M05
    G00 Y20.000
    M03 S500
    G01 X30.000 F100 S250 ; 1/4 power
    M05
    G00 Y30.000
    M03 S500
    G01 X0.000 F100 S125 ; 1/8 power
    M05
    G00 Y40.000
    M03 S500
    G01 X30.000 F100 S64 ; 1/16 power
    M05
    G00 X0 Y0 (home)
    M05
    M30
    
    of course we may need to adjust the feedrate up or down to get a useful speed for this test.
    Laser power is non linear anyway and power below half or 1/4 may never burn anything, at any feedrate.

    For every laser cut you have 3 variables,
    the material
    the power
    the feedrate
    so it will be handy to keep some power and feedrate test files for a quick test on new materials. old materials you will already know from your notebook. (-:

    always always wear the safety glasses!
     
  3. Scotty Orr

    Scotty Orr Journeyman
    Builder

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