Newbie Why no Z travel when cutting thicker material in multiple passes?


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Thread: Why no Z travel when cutting thicker material in multiple passes?

  1. #1
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    Question Why no Z travel when cutting thicker material in multiple passes?

    Total laser newb here, but I have been doing some initial research to possibly build a diode laser capable of cutting 5mm ply. I've built CNC and 3D print machines, so I am familiar with the mechanics of an xyz machine.

    One limitation I keep reading about diode lasers is that the point of focus is quite shallow. If you cut in multiple passes, the deeper you go the less in focus the beam will be. So, a simple question: Why not lower the toolhead for each pass? For example, if your focus length is 22mm and you are cutting 8mm in 8 passes, why not lower the head 1mm per pass? It seems like you would have plenty of travel before the laser itself interferes with the work piece.

    There must be an obvious reason. People with a lot of experience and training have spent more time than I can imagine trying to squeeze better performance out of inexpensive lasers. I'm just wondering what it is so I can finalize my build design.

    Thanks!

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    Default Re: Why no Z travel when cutting thicker material in multiple passes?

    I’m familiar with CO2 not diode but I assume they are similar. You always want to cut in one pass by adjusting air, speed at max power. Cut quality suffers when you cut twice as burning and charring increases.
    To your idea, I’m also not aware that the software changed Z between passes like other CNC machines do.
    There are techniques the cut a second pass from the backside which isn’t too bad on the finish, but alignment is tricky.


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    Default Re: Why no Z travel when cutting thicker material in multiple passes?

    FWIW, I had an engineer friend explain the problem and why subsequent passes are not refocused.

    If you focus lower on a subsequent pass the walls of the trench left from the earlier passes would interfere with the beam. At best they would block part of the beam reducing power, and at worse the surface would begin to char.


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Why no Z travel when cutting thicker material in multiple passes?

Why no Z travel when cutting thicker material in multiple passes?