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  1. #1
    Join Date
    Sep 2007
    Posts
    46

    Repaire Red Dot but my laser out of focus

    My Laser Engraver has a red dot for ease of focusing and positioning, suddenly it disappeared, so I did some circuit tracing and found that one of the wires that supplies it with 5 volts was broken, see pictures, I repaired that, now have my red dot, BUT the Laser is out of focus??? the test shows that my postioning is out about 1/8", I must have moved something!!! Amos


  2. #2
    Hi Amos,

    The single red dot isn't for focal use, it's for tracing the outline to ensure it's inside the bed area and/or where the machine will be.

    To get a red dot focal system you need two at a 90 degree angle to each other and run the convergence method. (Like the dam busters height sight)

    Red dot focal systems aren't very accurate though, they tend to be +/- 0.5mm at best and sometimes as bad as +/- 1mm+.

    I did build a much more accurate version but dropped the idea when it became apparent that it bases too much of the accuracy on the operators eyesight.

    A height gauge used from the gantry to the material works very well as would the addition of a linear scale (electronic type). I opted for the linear scale on mine and can now adjust the bed by resolutions of 0.01mm if I need to.

    best wishes

    Dave

    ps: use the ramp method to determine the optimal focal position, lens's with a 50.8 focal length can be as much as +/- 2mm out of that range in reality so gauging from the rear of the lens isn't accurate.

  3. #3
    Join Date
    May 2010
    Posts
    112
    I agree, the red dot is useless for accurate work. Your eyesight is not that good, especially when looking at the concentrated light of the red laser, weak as it is in comparison.

    You can get it lined back up though, the easiest way in my opinion is to take off the first mirror and side cover of the machine so the CO2 and red laser can escape straight out from inside the machine. Set up a piece of wood a good 10-20 feet away from the machine and test fire the laser, hitting the wood. It should make a fat 1/4" or larger mark on the wood, now you just need to adjust the red dot laser till it lines up with the center of that mark. After that just clean your mirrors and walk them back in.

    The stock red laser adjustment deal on my laser was crap, it was held steady (or it was supposed to be) by a piece of allthread around 8+ inches long. Used two jamb nuts to lock the entire thing in place. Engraving stuff jostled the allthread enough to put the red dot out of alignment. Completely and totally useless and really quite pathetic that gweike didn't use another fine adjustment optic holder like the mirrors use.

    Just rip it all out of the optic path and be done with it, you'll get some more laser power from it anyway.

  4. #4
    Join Date
    Sep 2007
    Posts
    46
    Thanks for those replies, they raise questions in my mind, up to now I have used the red dot to set the correct distance from my work in the Z axis. I did do the normal Laser alignment recently, have checked that and all seems ok, I did some minor adjustment last night and it is going ok. However, I am not one to settle for mediocrity, without a red dot system--how would you know the correct distance to the work in the Z axis?? Amos
    PS I am not conversant with the suggestions you have implemented on your machines, I would need to see pictures and diagrams and instructions, if they exist somewhere , please point me to them and I will research it before attempting any modifications. Thanks again, Amos

  5. #5
    Join Date
    Sep 2007
    Posts
    46
    Here is what I have achieved thus far, Amos



  6. #6
    Join Date
    May 2010
    Posts
    112
    You set the focal distance by measuring from the tip of the laser head to your work piece. I am not sure who told you that the red laser is to be used for focusing, but that is an incorrect statement.

    Using the red dot to aim the laser is a very bad thing to do, especially when the red laser is not at all part of the optical path of the CO2 laser. The red laser has no effect or relation on the focus distance of the CO2 laser, so trying to set the CO2 using the red laser is never going to be very accurate.

    You need to find your lasers focal point, by either trial and error or using the tilted board method. Measure that distance (from the laser head to the point where the laser mark is as narrow as possible.) and cut a piece of acrylic the same width. Now you have a "focus gauge." To focus you just move the Z table till your gauge just barely fits between the material and laser head. Does this make sense?


    The things I said in an earlier post don't apply to your machine.

  7. #7
    Join Date
    Sep 2007
    Posts
    46
    Thanks for the info, I will try what you have suggested and let you know how it goes. Amos

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