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Thread: Me Again: Newbie Epilog Laser: How to Reduce Char

  1. #1

    Me Again: Newbie Epilog Laser: How to Reduce Char

    Hi Again. You guys are always so helpful.

    I'm laser cutting Delrin/Acetal plastic, about .060" thick. I'm trying to reduce as much char as possible, as I have to sand and debur a lot right now.

    The machine is the entry-level Epilog Zing, rated at 30 Watts.

    I had mentioned the charring issue to the Tech Dept at Epilog before I fired up the machine, because I've been jobbing out the work for years and always found a lot of char, and he said something about playing with the Wavelength (Frequency).

    Eventually I'll be switching to CNC and/or waterjet, but I'm determined to solve this as much as possible with laser.

    Right now it's just trial and error, which is fine, the material is cheap, etc., but I'd like to find a way to speed up my learning curve.

    I have been running it as follows:

    SPEED: 50%
    POWER: 75%
    FREQ: 2500

    When the tech suggested playing with the Wavelength, which direction might lessen the charring, UP or DOWN?

    I've been trying to run a controlled experiment, where I change only one parameter at a time.

    I should add that I have an excellent air assist pump, as well as a superb exhaust system.

    Thanks in advance for your insights.

    Scott
    Last edited by Scott Memmer; 07-31-2020 at 7:23 PM.

  2. #2
    Join Date
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    SE South Dakota
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    I've owned 3 lasers over my "career", 2 of which were from the same mfgr. with same exact features.
    None would cut the same--I had to dial in the settings for various materials, speed, power, frequency etc.
    I'm thinking you may have to do the same?? Sorry.

    Bruce
    Epilog TT 35W, 2 LMI SE225CV's
    CorelDraw 4 through 11
    CarveWright
    paper and pencils

  3. #3
    Quote Originally Posted by Bruce Volden View Post
    I've owned 3 lasers over my "career", 2 of which were from the same mfgr. with same exact features.
    None would cut the same--I had to dial in the settings for various materials, speed, power, frequency etc.
    I'm thinking you may have to do the same?? Sorry.

    Bruce
    Apology welcomed but not required. I just like researching and gathering info, John; it's fun. And I don't mind the experimentation, other than the time invested.

    Perhaps someone will come along who owns a similar Epilog and share their strategies, although even there it will vary somewhat based upon the life of the machine, the lens, and other things. I got so lucky with this machine. It only has about 30 hours on it, and the young man who owned it was moving out of town and needed cash. It was on eBay, but he was only two miles from my home, so we worked a straight cash deal and bypassed eBay and Paypal.

    Thanks again, Bruce. Have a great weekend.

    Scott

  4. #4
    When I'm cutting 1/16" thick Rowmark or Duets, I run THREE passes, makes for much cleaner cuts. In your case, the 50% speed sounds fine, so try splitting your 75% power 3 times, and see what happens- if it works, then try increasing speed and power proportionally until you get the same results but a bit faster. Yes it takes more time, but so does cleaning up char

    also, experiment with covering the surface you're cutting with blue painters tape, and see if that helps. If it does, invest in some vinyl signage transfer tape.
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  5. #5
    I can't swear the following is absolutely correct but it is my understanding of what is going on. At least with RF lasers, the FREQ setting is sort of a laser firing rate control. I think you were the one who earlier mentioned testing on paper. Vector a line with the FREQ set at maybe 200 or more and you will cut the paper on that line. Set FREQ low enough (it depends on your speed) and you can create a perforated line (series of individual holes with spacing that depends on speed and frequency). With frequency set at maximum, you will be pumping the greatest possible energy (for your power and speed settings) into the substrate with whatever result that substrate invokes.

    So, for example, with acrylic, if you come up with a speed/power/mid-frequency setting that just cuts through the acrylic, the cut edge will be on the rough side because there is just enough energy to vaporize the kerf area to create the cut. If you then up the frequency to maximum with same speed/power and try again, the higher frequency will pump more energy (due to more pulses) into the cut, which adds heat, which not only vaporizes the kerf area but also melts the cut edges somewhat. The edges rapidly cool as the beam passes on and leaves a more polished look.

    Now, go back to paper. At low enough frequency, you get a perforated line. At higher frequency, the perforations come together and result in a continuous cut with cleanly vaporized edges. At a high enough frequency, you not only vaporize the cut line but also dump additional energy into the cut which heats the cut edges and causes them to char. You can eliminate the char by lowering the frequency, or by increasing the speed, or by reducing power, or some combination thereof.

    Sometimes, a plastic sort of substrate can have a strong tendency to distort from the heat (swelling, foaming, charring, etc.) and no amount of tweaking will result in a clean cut edge. About the best you can do is experiment to get the most/deepest cut possible without excessive (however you determine that) distortion, and then run as many passes as needed to completely cut through. This is what Kev mentioned when saying he ran three passes to cut 1/16" Rowmark. Any setting that cuts in a single pass will cause the edges to distort an "unacceptable" amount, but he found a setting that minimized the effect when repeated for 3 separate passes.

    Bottom line, you generally want the fastest speed that doesn't induce ringing, overshoot, or other speed-related problems. For typical lower power lasers (such as 30-80 watt), you are often power limited, meaning you can't cut at full speed even at full power, so I often start experimenting with max power and and max frequency, to find the highest acceptable speed that reliably cuts through. To reduce charring or other edge issues, reduce frequency until it stops or you can't reliably cut. If you get so low in frequency that you can't cut reliably or the edge is too ragged, you can try reducing the speed and iterating on power and frequency changes. If you can't find a suitable combination, start over with the goal of cutting at least half way through with an acceptable edge. If you succeed, add a second pass to cut the rest of the way, possibly tweaking settings a bit to attain the fastest final cut with cleanest edge. If you can't do that acceptably, try to cut a third of the way on the first pass, then repeat for second pass and a final third pass.

    Another consideration is whether this is for fun or profit. I don't know what sorts of things Kev does that he finds three passes acceptable but, for commercial projects of any complexity, I generally wouldn't do more than two passes because of the time/expense involved (both in experimenting to find acceptable settings and in production time). Maybe three passes is okay for cutting rectangular name plates, but cutting intricate shapes (such as a snowflake ornament or lacy design) becomes uneconomical with three long passes, at least on a gantry system. (It's not uncommon on galvo systems to run hundreds or thousands of passes but they are immensely faster.) Also, the time needed to come up with suitable settings is likely prohibitive for one-off or small numbers, but may be acceptable for personal projects or commercially for something like name tags that will bring lots of repeated orders from multiple customers.

  6. #6
    Quote Originally Posted by Glen Monaghan View Post
    Another consideration is whether this is for fun or profit. I don't know what sorts of things Kev does that he finds three passes acceptable but, for commercial projects of any complexity, I generally wouldn't do more than two passes because of the time/expense involved (both in experimenting to find acceptable settings and in production time). Maybe three passes is okay for cutting rectangular name plates, but cutting intricate shapes (such as a snowflake ornament or lacy design) becomes uneconomical with three long passes, at least on a gantry system.
    Agreed- however, I'll elaborate a bit: I don't do much if any 'intricate' cutting, most of my cutting involves round E-stop legends, rounded-corner labels, and 'snap' lines (cutting plate border lines about 1/2 way thru to be snapped apart after engraving). I'm fortunate enough to have many machines so the extra time usually isn't a big deal to me. When I cut in 3 passes, I just leave the factory masking on and cut thru that. The 3 light passes leaves minimal edge melt. But the factory masking isn't sufficient for clean-edged one-pass cutting. I cut a lot of 1/8" Ultramatte on the 80w Triumph, and I do it in one pass. But to do that requires masking BOTH sides with transfer tape. (which takes time, and money ) - As long as the laser's in good focus, I get pristine sharp edges, top and bottom. I don't know why transfer tape is such a good buffer/heat sink, but it is. If I don't mask the bottom, or only use the factory masking, I'll end up spending up to 1/2 hour with my Browning shaving the melted high-spots off the edges of a dozen 3 x 15 plates.

    Now, about RF 'frequency' settings-- is that just some new marketing jargon that sounds more sexy than 'dots per inch'? "Frequency" usually refers to measurements in TIME, not distance, but no law against that I guess -- Or are they actually incorporating 'dots per SECOND' laser firing? IMO that wouldn't even work on a gantry machine due the infinite speed changes... ?
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  7. #7
    Quote Originally Posted by Kev Williams View Post
    Now, about RF 'frequency' settings-- is that just some new marketing jargon that sounds more sexy than 'dots per inch'? "Frequency" usually refers to measurements in TIME, not distance, but no law against that I guess -- Or are they actually incorporating 'dots per SECOND' laser firing? IMO that wouldn't even work on a gantry machine due the infinite speed changes... ?
    Well, it certainly isn't "new". Every RF laser I've seen (primarily Epilogs and Universals, the oldest being from the mid-late 1990s) has had a frequency setting. And it has nothing to do with dots per inch, though there are also settings for that at least in Epilogs and Universals (however, it's for rastering and not vectoring). The frequency IS a time measurement but, when you factor in the notion that the head is moving at some particular speed, you can see how higher frequency of firing results in more laser pulses per unit distance while lower frequency results in fewer pulses per unit distance, and so it can be perceived as sort of a DPI. However, a specific frequency only converts to a DPI value when you also specify a speed; frequency and speed are independent and so frequency is NOT implicitly related to DPI.

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