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Thread: RF vs DC excited lasers... engraving/spot size question

  1. #1

    RF vs DC excited lasers... engraving/spot size question

    I've been using a 30 watt Epilog legend 32 for the past few years. Engraves beautifully. Or did until recently, but that's beside the point.

    How does the engraving of the chinese lasers using DC-excited glass tubes like Boss or Rabbit compare?

    I've been reading that the spot size out of the tube tends to be larger on DC excited tubes, resulting in a larger final spot size on work. But can that be mitigated with focus lenses? Is there any kind of rough equivalent like "2 inch focal lens in a DC excited machine is like a 3 inch in an RF" or something along those lines? Or does it not work that way?

  2. #2
    Dave Sheldrake will likely chime in with some actual knowledge on the subject -- in the meantime, from my experience and heresay

    I've used 3 RF lasers- my 25w New Hermes Optima (ULS), 30w GCC Explorer, and my 40w Gravograph LS900, all are in use daily (my BIL now owns the ULS)
    and my 80w Triumph is my only DC machine. Of these 4 machines, the spot size of the LS900 is about 2/3 the size of the other machines, very small. But, it uses a beam expander (collimator?) which helps with that I'm sure, wider incident beam equals smaller beam spot. My 25 and 30 watt machine's beam spot is noticeably bigger than the 900's. And, they're about the same size as the beam spot I get with my Triumph. Again, incident beam width of the 80w DC tube is larger than those on other 2 machines.

    As for engraving quality, my Triumph, which is a big 1300x900 'cutting' machine, I have it fine tuned to where it engraves as well as my other machines. The LS900 bests it only because the smaller beam spot makes it capable of better fine detail. However, the Achilles heel of the Triumph is speed, if I raster much above 500mm/second the quality begins to suffer, which I attribute more to the DC tube's slow-firing characteristics than anything mechanical. So while it gets the job done, and nicely, the 500mm/s speed is 4x slower than the GCC and 900's roughly 2000mm/s speed. And the Trotec speedy's and LS900XP machines run at roughly 3800mm/s!

    All the RF lasers are Synrads, the DC is a RECI...
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  3. #3
    Quote Originally Posted by Kev Williams View Post
    Dave Sheldrake will likely chime in with some actual knowledge on the subject -- in the meantime, from my experience and heresay

    I've used 3 RF lasers- my 25w New Hermes Optima (ULS), 30w GCC Explorer, and my 40w Gravograph LS900, all are in use daily (my BIL now owns the ULS)
    and my 80w Triumph is my only DC machine. Of these 4 machines, the spot size of the LS900 is about 2/3 the size of the other machines, very small. But, it uses a beam expander (collimator?) which helps with that I'm sure, wider incident beam equals smaller beam spot. My 25 and 30 watt machine's beam spot is noticeably bigger than the 900's. And, they're about the same size as the beam spot I get with my Triumph. Again, incident beam width of the 80w DC tube is larger than those on other 2 machines.

    As for engraving quality, my Triumph, which is a big 1300x900 'cutting' machine, I have it fine tuned to where it engraves as well as my other machines. The LS900 bests it only because the smaller beam spot makes it capable of better fine detail. However, the Achilles heel of the Triumph is speed, if I raster much above 500mm/second the quality begins to suffer, which I attribute more to the DC tube's slow-firing characteristics than anything mechanical. So while it gets the job done, and nicely, the 500mm/s speed is 4x slower than the GCC and 900's roughly 2000mm/s speed. And the Trotec speedy's and LS900XP machines run at roughly 3800mm/s!

    All the RF lasers are Synrads, the DC is a RECI...

    Great info, thanks! The tube on my Legend 32 is a synrad J48-2. "epi" revision. Nominally a 25W rated tube, but driven to output 30 watts for epilog, from what I understand.

    So it's not just about spot size but the frequency the tube can fire at. More of a speed costs money thing? I'm willing to trade speed for cost but the quality of the final product is not something I'd like to compromise on. Or at least not much.

  4. #4
    Join Date
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    I have seen that my Chinese lasers are unable to run (fire) as fast as my Epilog. In doing inlays, the Chinese lasers need to run relatively slow to get clean deep "cuts" for the inlays. However, my daughter (who took over the business) never bothers with the Epilog and uses her Shenhui exclusively (mostly for the larger bed) . We've never had a customer notice any difference in the engravings between the machines.
    Longtai 460 with 100 watt EFR, mostly for fun. More power is good!! And a shop with enough wood working tools to make a lot of sawdust. Ex-owner of Shenhui 460-80 and engraving business with 45 watt Epilog Mini18.

  5. #5
    Join Date
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    Olalla, WA
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    A long time ago I posted photos of the Aztec calendar that Epilog sends out as samples against one made on my machine using an 80W Reci. Here they are again;
    Attached Images Attached Images
    Shenhui 1440x850, 130 Watt Reci Z6
    Gerber Sabre 408

  6. #6
    Kev's got it pretty much covered

    RF's provide a better beam profile in most cases so you tend to be able to use more of the available power, RF's fire orders of magnitude faster as well, in effect almost instant where as DC have a delay while the charge builds and forms the plasma.

    Spot size is a product of incident beam / M^2 / Focal length so not really much in it

    Kev's right again, at 2,000mm per second even a good DC tube will struggle trying to keep up without losing quality where as an RF will handle that easily
    You did what !

  7. #7
    Quote Originally Posted by Dave Sheldrake View Post
    Kev's got it pretty much covered

    RF's provide a better beam profile in most cases so you tend to be able to use more of the available power, RF's fire orders of magnitude faster as well, in effect almost instant where as DC have a delay while the charge builds and forms the plasma.

    Spot size is a product of incident beam / M^2 / Focal length so not really much in it

    Kev's right again, at 2,000mm per second even a good DC tube will struggle trying to keep up without losing quality where as an RF will handle that easily
    Excellent, thanks for the great info, guys.

    Now I need to figure out what my Legend 32's x axis linear speed is to see how those numbers compare to what I'm used to. Doesn't say it in the spec sheet or manual anywhere.

    I guess I could bump the speed down to 1 percent and time how long it takes to travel the length of the bed, then multiply that by 100 to get Time in seconds per 32 inches?

  8. #8
    I wouldn't trust 10% speed to actually be 10% I like full-speed testing... run the laser at 100 speed across it's entire length, whatever that might be, 32" I'm assuming... Start a timer when the machine starts. Count each left-right and right-left sweep... at 100 sweeps, stop the timer. From there, calculate the time it took to run off the 3200 inches to find your inch per second speed. Deduct around 10% to compensate for the stop-restart time at the end of each sweep, and you should be pretty close

    >edit< - a little research says you have servo motors in that thing, so you SHOULD be at least somewhere into 80 inch/second territory, which is ludicrous speed compared to 500mm/s
    Last edited by Kev Williams; 07-04-2018 at 1:26 PM.
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  9. #9
    Quote Originally Posted by Kev Williams View Post
    I wouldn't trust 10% speed to actually be 10% I like full-speed testing... run the laser at 100 speed across it's entire length, whatever that might be, 32" I'm assuming... Start a timer when the machine starts. Count each left-right and right-left sweep... at 100 sweeps, stop the timer. From there, calculate the time it took to run off the 3200 inches to find your inch per second speed. Deduct around 10% to compensate for the stop-restart time at the end of each sweep, and you should be pretty close

    >edit< - a little research says you have servo motors in that thing, so you SHOULD be at least somewhere into 80 inch/second territory, which is ludicrous speed compared to 500mm/s
    Yeah, 4 times faster. Whoo boy. When I'm doing event plaques, I know at 600 dpi, a 6.5" x 5" plaque (arranged verically) takes about 18 minutes to raster. Adding additional plaques along the X axis seems to add about 1.5 to 2 minutes per plaque. So I can do 6 event plaques in about 26 to 28 minutes. Or 12 in 52 to 56 minutes. I guess I'm officially spoiled... I don't know if I could live with jobs I'm used to taking 1 hour taking 4 hours.

    I'm guessing the speed limitation afforded by the DC excited tubes is part of why the Chinese machines don't bother with servos. Can't take advantage of the higher speed they could get with servos, so might as well use steppers.

  10. #10
    Join Date
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    Savusavu, Fiji
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    In my limited experience, you really have to run the actual job on a machine to see how long it takes. That said, if you are pushing things out the door as fast as you can make them, the Trotec Speedy series sound like the best you can get.
    Longtai 460 with 100 watt EFR, mostly for fun. More power is good!! And a shop with enough wood working tools to make a lot of sawdust. Ex-owner of Shenhui 460-80 and engraving business with 45 watt Epilog Mini18.

  11. #11
    The bang for the buck with DC vs. RF lasers is that RF lasers can't outrun them when used for vector cutting. There are a few benefits to cutting with an RF but speed usually isn't one of them, simply because sheer power is whats needed, and big DC tube power is cheap

    And in the for what it's worth category, the Gravograph LS900XP is faster than any Trotec
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  12. #12
    Quote Originally Posted by Kev Williams View Post
    The bang for the buck with DC vs. RF lasers is that RF lasers can't outrun them when used for vector cutting. There are a few benefits to cutting with an RF but speed usually isn't one of them, simply because sheer power is whats needed, and big DC tube power is cheap

    And in the for what it's worth category, the Gravograph LS900XP is faster than any Trotec
    We’ll never know because apparently no one has one and it’s speed is so remarkable that they only show it vector cutting on their own website

    Keep an eye on the classified forum here, people put some nice lasers up for sale from time to time
    Lasers : Trotec Speedy 300 75W, Trotec Speedy 300 80W, Galvo Fiber Laser 20W
    Printers : Mimaki UJF-6042 UV Flatbed Printer , HP Designjet L26500 61" Wide Format Latex Printer, Summa S140-T 48" Vinyl Plotter
    Router : ShopBot 48" x 96" CNC Router Rotary Engravers : (2) Xenetech XOT 16 x 25 Rotary Engravers

    Real name Steve but that name was taken on the forum. Used Middle name. Call me Steve or Scott, doesn't matter.

  13. #13
    Out of all the Trotec vids I could find, I found exactly two 3-second blips of high-speed running. There may be more, but aside from that, why both companies seem to focus more on the cutting than high-speed engraving in their advertising escapes me. Could be because the DC lasers are so good at it?

    But while scrounging around I came across the LS1000XP, which I haven't heard much about- What a machine, 24x48" work area with 4-side material pass-thru, 4m per second raster speed (Trotec is advertised at 3.55m per second, what can I say? ) - and this was the only vid I could find of either XP engraving- since the helmet it's engraving is only 2-3/4" long the high speed doesn't even come into play- but it does an impressive job of cutting thru the 1" plex!

    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  14. #14
    If the machine is as fast as they say it is, then someone should fire their marketing team because with 1000's of people on this forum, and we've never seen one person ask about it, buy one, or show one they own. I guess it's one of the best-kept secrets in the business I've been to many trade shows and I've never seen one or seen one running. You'd think they'd be shouting it from the rooftops, but apparently, they are happy with no one in the industry knowing about it Let's keep in mind, the Speedy 300 has been out, pretty much unchanged, for more than 10 years. Good to see other's finally catching up
    Lasers : Trotec Speedy 300 75W, Trotec Speedy 300 80W, Galvo Fiber Laser 20W
    Printers : Mimaki UJF-6042 UV Flatbed Printer , HP Designjet L26500 61" Wide Format Latex Printer, Summa S140-T 48" Vinyl Plotter
    Router : ShopBot 48" x 96" CNC Router Rotary Engravers : (2) Xenetech XOT 16 x 25 Rotary Engravers

    Real name Steve but that name was taken on the forum. Used Middle name. Call me Steve or Scott, doesn't matter.

  15. #15
    Seriously, I don't understand the lack of advertising either- I know most of the larger/expensiver stuff is aimed at large companies mass producing product that they want to mark/identify in-house. 8 years ago I wanted some aluminum parts test engraved on a Gravo YAG to see if buying one was viable- my rep had to go to send it 2 states away to the closest YAG he sold, and this place had 15 of 'em at $40k a pop. Also, G-graph has a solid old-time customer base, of which I'm one. But many of them- of which I'm one- have a hard time with the prices of their machinery. I have 12 in-use New Hermes/G-graph machines purchased between 1982 and 2013, but only 4 of them were bought new, and LS900 was a 'last year' model I got at a good price. The newest of them is my IS400, and it's around 8 years old. And after using all these machines for all these years, my only "non-maintenance" shutdowns have been 2 power supplies, the first (LS900) was overnighted from France the next morning, the other (IS7000) my rep had a replacement here within an hour. Their machines are bulletproof, and at least in my case, so has been the customer service. But then, the fact I've hardly ever needed any helps!

    I've never advertised, never needed to. Could be G-graph feels they don't need to?
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


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