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Thread: Using a 100mm lens

  1. #1

    Using a 100mm lens

    Hello, I have a job coming up cutting a fair amount of 3/8" plywood. I am curious to know if it would be worth switching to a 100mm focus lens. I do have one available, however I have heard that with the Rabbit laser, I will need to drill the hole in the focal head a bit bigger in order to use it without losing power. My biggest question is will using it allow me to cut faster than my 2"?

    My second question is whether or not anyone has modified the focal head and what is all involved? I have tried to find the article on Rabbit's website, but the file is not available. Besides reading a guide, there is often more knowledge in a multitude of counsel. Thank you for your time.

  2. #2
    Disclaimer: I don't do that much cutting with any of my machines, and my 'cutting' machine is an 80w Chinese machine-

    that said- the testing I've done has shown me that I get the fastest and best results with a basic 2"/50mm lens. I couldn't get a 3" to match the speed, and a 4" was ridiculous. I came to the quick conclusion that 3 and 4" lenses, to be efficient, need WAY more power than my 80 watts...

    As for drilling the hole, are you talking the mirror-hole, or the cone? I believe part of my problem with longer lenses was the cone hole was too small. I didn't drill it out, I just removed it, haven't looked back.

    Awhile back I bought a 2-1/2" / 63mm lens, and it's a great lens, not much power loss, more leeway in focusing, I've noticed no difference between it and a 2" lens other than the focus distance! Cuts and engraves the same as a 2"...

    And a thought about cutting deep, resist the urge to focus farther down into the material to compensate for focus distance. It's counter-productive because the focused spot is where the ultimate power density is, and remember the beam is angled- when you focus below the surface, a significant amount of out-of-focus, lower power laser light is being absorbed uselessly at the material's surface, and that power is no longer available at the focused spot. So while theoretically you can cut deeper by starting deeper, the focused spot will have less power density, which will reduce cutting depth rather than increase it...
    ========================================
    ELEVEN - rotary cutter tool machines
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  3. #3
    Join Date
    Mar 2014
    Location
    Iowa USA
    Posts
    3,369
    How much power does your machine have? The longer lens would give you a great depth of field, might even give you a larger dot size and make things worse.
    Retired Guy- Central Iowa. , LightObject 40w CO2 Laser and Chiller, MakerGear M2 3D Printer. Fine Line Automation 4x4 CNC Router- Mach4 ESS

  4. #4
    Hello, my machine is 100W.

  5. #5
    Join Date
    Mar 2014
    Location
    Iowa USA
    Posts
    3,369
    I'd say go for it.
    Retired Guy- Central Iowa. , LightObject 40w CO2 Laser and Chiller, MakerGear M2 3D Printer. Fine Line Automation 4x4 CNC Router- Mach4 ESS

  6. #6
    I did not realize, but the 'lens holder' part of the focal assembly has an offset in it to put the lens in for either a 2" or 4" lens, so no modifications needed. There is not a huge difference in solid wood, but it does seem to not cut as well in plywood. I have not played around with the settings much yet, but it was an easy fix.

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