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Thread: CNC Laser Engraving 8bit Shades of Grey 445nm

  1. #11
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    swamidog is offline Jr. Woodchuckington Janitor III, Esq.
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    best of luck! your project is awesome and i will for sure be following in your footsteps.

    c.


    Quote Originally Posted by JJWMACHINECO View Post
    Thank you for that information, but I have already invested way to much with DTR on 445nm diodes and lenses already to change directions now. I have not seen or know of anyone using a 405nm to laser engrave photographs, but there are several I know of that do use the 445nm. I'm going to try experimenting with the optics first.

    Jeff
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

  2. #12
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    That's great,

    Will be looking forward to see your engravings in the future. There is allot of information about laser diode engraving here also. http://hobbycncart.com/forum/63-151-1

    Here is an engraving I did on the back of a mirror using analog modulation. It's like a Lithophane, except the image is visible when it's back lit or not. The first picture is back lit and the second one is not. I actually do get some shading on a mirror also.

    Jeff
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    Extensively Re-worked/Re-designed/Modified Servo K2CNC KG-3925, Mini Diode Laser Engraver and now a Shapeoko 2 Laser Diode Engraver.

    https://www.picengrave.com

  3. #13
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    You can get a smaller spot size by using a shorter focal length (ie, laser closer to the piece of wood), which will probably require a 2 lens setup. You can use your current 3 element lens to get a collimated beam and a 2" or so focal length lens to refocus. With a setup like this it should be able to get about half of your current spot size, and you can get even better if you use a longer focal length collimating lens on the laser (to get a larger starting beam size). In a 1:1 imaging configuration (ie, using a 2" focal length lens for both the laser and the refocusing, good luck finding that lens!) it should be possible to get a roughly .001" spot size with a normal multimode 445nm laser diode.

  4. #14
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    I have a G2 single element glass lens here and a few 3 element glass. Maybe I can use the G2 near the diode and then shoot the beam through a 3 element afterwards and see how that effects the focal spot size. It's worth a try. If I can get the beam half the size that I get now when focused on the wood, that would be good enough to achieve the detail I'm looking for.

    Thanks. Jeff
    Extensively Re-worked/Re-designed/Modified Servo K2CNC KG-3925, Mini Diode Laser Engraver and now a Shapeoko 2 Laser Diode Engraver.

    https://www.picengrave.com

  5. #15
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    With these very bright diodes it can be difficult even to measure the actual spot size. Krazer is right when he describes the typical optical set up for focusing a diode or fiber/diode laser source. Two lenses with the first placed at its focal length from the source to collimate and then a second lens placed at its focal length from the target to focus. If the lenses are of equal focal length then the magnification ratio is one. As the focal length of the second lens becomes shorter relative to the first then the magnification is less than one (by that ratio) and the focal spot shrinks (by that ratio). Given the same RATIO for the focal lengths then if the focal lengths of the lenses are longer the lens aberrations decrease and the requirements for aspheric, achromatic or multi-element lenses decreases. These more advance lens designs don't hurt except for their cost and in the case of multiple elements there might be a little less throughput. However you do it, the collimated beam between the lenses is a good place to put a low transmission filter such as a welding window that will allow you to inspect the focus (with out going blind or destroying your camera). The parallel rays in the collimated beam will not be shifted by the filter causing a spherical aberration component to mess up your adjustments and adjusting @ near full power is important to getting the best spot when running @ near full power.

  6. #16
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    I can get the focal spot the smallest initially by projecting it onto a black anodized piece of aluminum. The beam does not reflect, so I can see it when wearing my safety glasses as I adjust the lens to make it the smallest. How I am able to measure the focal spot is measure the burn line by scanning the image on my scanner and bring the image file it into my cad program. I make sure it is to scale and then I measure it with the coordinates in my cad program. It's the burn line is what I am trying to get smaller which should correspond with the focal spot diameter. Right now the burn line is .007" wide and it does not change width though the power levels or shades differences. My software allows me to set the stepover distance to the next burn line.
    Extensively Re-worked/Re-designed/Modified Servo K2CNC KG-3925, Mini Diode Laser Engraver and now a Shapeoko 2 Laser Diode Engraver.

    https://www.picengrave.com

  7. #17
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    Great work. Looks like you are getting some great results with the setup you are using. I will say a lot of my CNC customers do tend to gravitate toward the 405's for the spot size they can achieve and the power density it provides but there are also those that have had very good results with the 445's as well.

    Here is link I like to give that has some estimates on power density with 405 vs 445.
    http://laser530.blogspot.com/2011_04_01_archive.html

    Here is a really neat project as a proof a concept one of my customers recently did as well.
    http://laserpointerforums.com/f54/mi...her-78491.html

  8. #18
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    Thanks DTR,

    There are several that has purchased the Nichia 445nm at my recommendation from you because of the high wattage output, even the author of the image to gcode program I use.

    http://www.ebay.com/itm/180948107479...84.m1438.l2649

    Engraving speed is also important with this process and I can not see the 405nm be able to achieve the higher speeds as the 445nm does.

    Reading that laser530 link you posted, the smallest spot he was able to focus the 445nm down to was .4mm and with optics available today, I am able to focus down less then half that size. My laser engravings come out very good already with the lens I have, but I am always looking into any improvements I can get.

    I did purchased two of the Nichia's from you awhile back for my next build where I mounted them at a slight angle and focused the beam to the same intersecting focal point. I'm running both of them at 2A max, slightly less as you recommended and was able to engrave at 150IPM. My build was successful, except the machine I mounted it on had to much vibration running at that speed and was effecting the image quality. I attached a picture of the results using badpip's dual analog modulation driver. You can see the vibration I was getting with the machine.

    I am in process mounting it on another CNC router that can handle the higher feedrates without any vibration and I should be able to laser engrave at 200IPM with it.

    Jeff
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    Extensively Re-worked/Re-designed/Modified Servo K2CNC KG-3925, Mini Diode Laser Engraver and now a Shapeoko 2 Laser Diode Engraver.

    https://www.picengrave.com

  9. #19
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    I have a suggestion. Seeing as earlier you said that speed is not a critical issue and the spot size is, then why not explore the 405 diodes even if only to learn the merits. Personally, I find the design/engineering of these optical systems very rewarding and you might too. That isn't to say they always work,but you learn a lot in the process. Once you have your second router up and running, you might consider installing on the first router, a dual 405nm diode set up with each diode mounted at 90 degrees to each other and offset 90 degrees in rotation about their optical axises. This will allow you to combine them with a PBS without the need for a 1/2 wave plate and the resulting 1+ watt beam should be able to focus very tightly. The energy intensity at the focus might even allow FASTER scan speeds. A higher quality beam will also permit a less aggressive demagnification and hence a greater depth of focus on the target. There is also the greater absorption of many materials at 405nm vs 445nm. Some, although it's had to say how much of the additional power of the 445 diode is reflected and decreases the effective absorbed energy on target.

    Your results are impressive and I don't mean to suggest that you aren't doing this right. Just thought you might want to consider these issues.

  10. #20
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    Thanks for that information and compliment. That is a good idea for a test I could do in the future with a 405nm and my mini router when I get my other one up and running. Also I was comparing time of the diode engravings with a CO2 and even at a feedrate of 150-200IPM is slow for a comparison.

    Jeff
    Extensively Re-worked/Re-designed/Modified Servo K2CNC KG-3925, Mini Diode Laser Engraver and now a Shapeoko 2 Laser Diode Engraver.

    https://www.picengrave.com

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