Laser cutting carboard

New Home Forum Mostly Printed CNC – MPCNC Advice – MPCNC Laser cutting carboard

This topic contains 68 replies, has 6 voices, and was last updated by  Jason Dentler 1 year ago.

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  • #68726

    Jason Dentler
    Participant

    2.8W jTech laser vs. 8 months of saved Amazon boxes…

    2 passes @ 200 mm / min: I almost set the top ablaze, but only got a few singe marks on the bottom. It wasn’t what I’d call a cut – just some burn marks.

    MVIMG_20180908_200729

    5 passes @ 500 mm / min: The lines were a lot cleaner and I got a few very tiny cuts on the bottom, mostly around the sharp corners.

    IMG_20180908_200654

    What settings would you guys suggest?

    #68732

    Barry
    Participant

    I think air assist would help.  Keeps it from flaring up.

    #68741

    dkj4linux
    Participant

    A fan and shroud are a necessity for cutting cardboard cleanly and without flareups. In the following video, 3mm cardboard is being cut in one pass at full power and 100 mm/min with a Banggood 3 watt laser… no air assist used here (though provision is made for it), but the shroud directs a steady stream of air onto the cut area to clear smoke and suppress flames…

    20170118_171858

    141603_324fb8043d2e0682f55a13466ef0894f

    141604_02c82f3b2bb18e2c649362f8b746ef10

    The procedure I use to determine feed and speed is described in the following post…

    https://www.v1engineering.com/forum/topic/mpcnc-inspired-corexy-laser-engraver/#post-36423

    — David

     

    3 users thanked author for this post.
    #68780

    Jason Dentler
    Participant

    Thanks guys! I’m not quite dialed in where I want it to be, but that helps a bunch.

    I have a shroud and fan assembly. The fan blows across the laser’s heat-sink and then narrows down to about a 8mm hole near the work surface. My idea was to create positive pressure inside the shroud and enough of a breeze coming out the end to clear the smoke near the work surface.

    Here it is without the laser shielding in place.

    IMG_20180809_235440

     

    #68788

    Jason Dentler
    Participant

    I think I just had it too close to be in focus, and in one spot it started to drag on the cardboard because of cupping.

     

    Here’s the results after raising it up a few mm.

    #68790

    dkj4linux
    Participant

    Ryan has already supplied exactly what is needed… his laser focus script

    https://www.v1engineering.com/forum/topic/laser-focus-script/

    Easy to use for any material thickness… intentionally lower Z to “too close” and run the script. Ten lines are drawn 1mm apart, each 2mm higher than the one before. Count lines back to best focus, multiply by 2mm, and lower Z back down by that amount. Here, call it 6  lines back… lower Z by 12mm and you are ready to run your job  🙂

    142341_e00429017143648a58d53fdb8f904ca2

     

    1 user thanked author for this post.
    #68800

    Jason Dentler
    Participant

    IMG_20180909_204321

    My focus test… 7 lines down, so I lowered it by 14mm.

     

    IMG_20180909_204501
    Underside of my speed test

    IMG_20180909_204533
    Top of my piece, cut at 73mm/min… It almost caught fire.

    IMG_20180909_204523

    Bottom… It didn’t cut through completely

     

    The test piece and the actual cut are from the same cardboard box, so it’s not a variation in the materials.

    I’m stumped. I suspect I need to do multiple, faster passes to avoid burning, and lower the laser a scootch with each pass.

    #68809

    dkj4linux
    Participant

    Your focus pattern doesn’t look right… you should see 10 lines and a very distinct difference near focus. Just like in my photo…

    A quick way to see if you are in the 20mm of range for the script…

    I send M106 S2 (you may need more depending on your laser’s threshold) from the sender program to turn on a very dim beam… barely on. Move the Z-axis down very close to the material and then use the manual Z controls to raise the laser… watching the beam closely. It should get smaller/tighter until the absolute sharpest/smallest dot is attained… that should get you close. Then, lower Z from there 10mm and rerun the script. Your pattern should look very much like the one in my photo… with the sharpest lines near the middle.

    When you get a properly focused beam at the top of the material, your 2.8 watt laser should cleanly cut completely through in one pass. I’ve had at least 4 or 5 different lasers in the 2.8 – 3.5 watt range and all have successfully cut through 3mm cardboard in a single pass at 100 mm/min and full power. Sharp focus is crucial, however… it’s an energy “thing”.

    This very issue was discussed — and solved for at least 2 other people — in my lengthy thread over on the FliteTest forum, if you’re still unconvinced and care to wade through it…

    https://forum.flitetest.com/index.php?threads/cutting-foam-sheets-with-a-needle.24251/page-44#post-322081

    The discussion, between me and 2 others, is scattered over the next 3 or 4 pages and the bottom line was:

    It’s power, feed, fan, and… focus, Focus, FOCUS!

    — David

     

    #68822

    Jason Dentler
    Participant

    Thanks David.

    The 10th line is the squiggly one, because I was dragging the laser & shroud across the cardboard.

    My Z holds without the steppers engaged, so I can turn it by hand. I’ll give that a shot.

    #68830

    Ryan
    Keymaster

    You should be able to twist the lens to change the focal distance. You need a bit of room between the work and your shroud or no air will move. So lasers list the “ideal” focal length somewhere in the range of 2″-5″. The laser should have no issues getting through cardboard. You seem to have way too short of a focal distance so your beam is diverging too fast and not making it through the backside. Really the longer the better, and easier to fine tune with the script.

    2 users thanked author for this post.
    #68845

    dkj4linux
    Participant

    Thanks, Ryan. I should have mentioned that I initially set up the focus for all my lasers to about 55mm or so… for smallest spot by adjusting the lens barrel. As received, they all focused much closer and there would not have been sufficient room for a shroud. I suspect that is indeed the case here…

    1 user thanked author for this post.
    #68904

    Jason Dentler
    Participant

    Since the shroud suffered some minor damage during a collision, I printed a new one with the laser closer to the tip of the shroud…

     

    I was also prepared to twist the lens, but figured I’d see where I was at first.

     

    You were correct, David. The focus point was up inside the old shroud.

    IMG_20180911_153438

     

     

    #68907

    Jason Dentler
    Participant

    Testing image upload…

    #68909

    Barry
    Participant

    Testing image upload…

    nope!

    #68910

    Ryan
    Keymaster

    I almost have that picture issue figured out. If you switch browsers it should work. There are only two of you that seem to be having the issue. Maybe a plug in or something.

     

    1 user thanked author for this post.
    #68911

    dkj4linux
    Participant

    We at least know the issue now. The first thing that really needs to be done with these lasers is to adjust the focal length… just as Ryan explained. I’m sorry I didn’t mention that up front.

    The easiest, and least dangerous, way to set the focal length IMO is to raise the Z-axis so that the lens is 2-1/2″ or so above the material. Turn on the laser at absolute MINIMUM power (M106 S2 does it for mine) so that you see the beam on the material and then screw the lens barrel out until you get the smallest dot you can… the laser won’t hurt/burn/cut you, at that power, as you mess with the lens barrel. Once that’s accomplished, that becomes your laser’s new focal length and you should now also have room for your existing shroud. In use, my shroud is only 5mm-10mm above the top of the material… it doesn’t need to be too much and insures good strong airflow.

    1 user thanked author for this post.
    #68960

    Jason Dentler
    Participant

    New shroud… IMG_20180911_143333

    My laser is 1″ closer to the tip of this shroud, and best focus on the test pattern was around 14 to 16mm, so that means the focus point was around 10mm up inside the old shroud.

    IMG_20180911_153438
    IMG_20180911_155158

    So, I’m pretty sure I’ve got a good focus now. However, I’ve still got a problem cutting through cardboard before it burns.

    At my new height (Z15), the almost-burning-down-the-house line is 50mm / min and 25mm/min increments with each line over.

    IMG_20180911_163340

    On the back, you can see 50mm / min cut through and 75mm / min scorched the bottom layer – but both of these are terribly burnt on top.
    IMG_20180911_163348

    This test was with the windows off the shroud, so I had a gentle breeze at best. I’ll try again later today with the windows in place so the fan blows through the tip on to the cardboard.

    #68968

    Jason Dentler
    Participant

    I think the next test needs to be power from the driver to the laser. Something is still off.

    #69015

    Jason Dentler
    Participant

    With the windows back on, so some air blowing… at 16mm above the top of the cardboard

    IMG_20180912_155507

    50mm / min – complete cut, some burning

    75mm / min – almost cutting, some burning

    125 mm /min – not cutting, no burning

     

    #69019

    Ryan
    Keymaster

    mm/s?

    #69031

    Jason Dentler
    Participant

    mm/s?

    yeah, sorry…

    For the complete cut, I did

    G1 <stuff here> F50

    and for the almost-cut, I did

    G1 <stuff here> F75

     

    #69034

    Ryan
    Keymaster

    F50 = 50mm/min = 50/60 = 8.3mm/s

     

    1 user thanked author for this post.
    #69052

    dkj4linux
    Participant

    IMO it still doesn’t look like you are focused at the surface of the cardboard. What are you measuring to get 16mm… from top of material to what? Also, put the windows on your shroud… always! The concentrated air-flow is crucial to clearing smoke and suppressing any flames. Something you might want to consider is eventually replacing the small fan that comes with the laser module with a higher-CFM fan… this provides a great deal more air-flow than the lower-CFM fan. Even without the fan upgrade, however, you still shouldn’t be having flame ups… but the shroud needs to be completely enclosed.

    20180912_183430

    No measuring is required if you’ll use Ryan’s focus script… I’ve got it assigned to the #1 custom button in RH. I run it routinely just before I start a laser job and it never fails to work. The photos below shows the sequence… lower Z until the shroud is within a couple of millimeters (eyeball it!) of the material, run the focus script, adjust back down 18mm (2nd line is CLEARLY best focus), a few millimeters adjustment “north”, set zero (G92 X0 Y0 Z0), the engraving run (full power, 800 mm/min), and then the cutout run (full power, 80 mm/min). The through-cut is clean and not burnt on both sides… I tried 100 mm/min and it didn’t quite cut through on one side of the logo; i.e. I wanted it to fall out when I picked it up! 😉  Used Inkscape and the JTech laser plugin for all gcode and RepetierHost to send it to Mega/RAMPS combo.

    20180912_182847

    20180912_182822

    — David

     

     

     

    1 user thanked author for this post.
    #69068

    Jason Dentler
    Participant

    I lowered the tip of the shroud on to the top of the cardboard, then raised it 10mm and ran Ryan’s script. The third line from the bottom was the best, so I came up with 16mm total from the top of the cardboard to the tip of the shroud.

    After that change didn’t give me great results, I popped off the windows and focused the bean by hand like you suggested.

    Thanks again for all the advice and patience, David.

    This is where I’m at now… I still have some burning when I go slow enough to cut through completely, and I really don’t have a super fine line from the focus script (but still thinner than the lines above and below).

    #69079

    dkj4linux
    Participant

    Here’s the entire video of the run I described in my previous post… no timelapse, no speed-up, just boring real-time…

    2 users thanked author for this post.
    #69088

    Jason Dentler
    Participant

    More data… I connected the multimeter to the laser out on the driver.

    M107

    MVIMG_20180913_075336

    M106 S127

    IMG_20180913_075459

    M106 S255

    IMG_20180913_075417

     

    This matches the recommended 1.5 amps for this particular diode (jtech 2.8w)

    #69107

    Jason Dentler
    Participant

    I emailed jTech customer support this morning. I’ll see what they recommend. Besides a beefier fan, I’ve tried everything you guys have suggested.

    #69118

    Ryan
    Keymaster

    Did you point them to this thread, it might help. They jump in here occasionally.

    #69126

    Jason Dentler
    Participant

    I didn’t think about it. Sorry

    #69127

    Jason Dentler
    Participant

    A little off topic, Ryan… What oscilloscope did you buy? Are you happy with it?

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