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Thread: Power, speed and PPI/Hz relationship

  1. #1
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    Power, speed and PPI/Hz relationship

    Being a complete novice at this game I am still struggling to get my head round how the relationship between power, speed, PPI/Hz affects each material and the best settings for each.

    Is it better to have higher power and speed or lower power and speed?

    i think, in the case of acrylic anyway, the higher PPI the cleaner the edge finish when cutting but how does the PPI setting affect MDF, Mylar and paper/card?

    I will mainly be cutting/engraving Mylar, MDF and acrylic so would someone be able to explain the relationship and how they affect the above materials?
    Speedy 300 80W
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  2. #2
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    The faster the speed the more work you can do every day, and faster means more power to cut it through cleanly. While a high PPI/Frequency is great for acrylic, it can cause more charring on materials like wood, MDF and paper. Over time you will find the sweet-spot for various materials and end up with a long list of settings to refer to that improves on the manufacturer suggestions. For engraving, it depends on how deep you want to go, for paint filling for example, you want to go deeper so more power and slower speed. For some wood or bamboo plaques I'll go 100% power and very slow speed to get a real deep, almost sandblasted look. The most difficult settings, that require some practice testing, are those with multiple layers of different density. For example, melamine on MDF, or Wilsonart type laminate on acrylic.



    Sammamish, WA

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  3. #3
    Graham, it's my understanding that the machine is pulsing the laser. Think of the beam like a sewing machine. Low PPI means the pulses are not as frequent, higher PPI, the pulses are more frequent. It affects different materials in different ways. Some (myself not included) think that higher PPI on acrylic gives a better finish because it's pulsing really fast and it keeps the heat in the cut and keeps the acrylic melting and gives a better edge. I've not found that to be the case, but my experience might not be typical. Then you have things like Mylar that melt super easy and doesn't like a lot of heat. A high PPI on Mylar would tend to increase the melting, so you'd want to use a lower PPI with that.

    It works for engraving and vector cutting the same way. You might engrave a certain piece of wood with a low PPI and it doesn't turn dark enough for you. On some woods, you can increase the PPI and it'll pulse more times in the area and give you a darker burn.

    There really isn't a "one size fits all" thing. It's very dependent on the job you are doing, what you are trying to accomplish, and what your material is and how it's reacting to the cutting or engraving.

    I wouldn't worry too much about it at this point. You can always pick "Auto" on the Trotec and let it pick something for you. That works pretty decent.
    Lasers : Trotec Speedy 300 75W, Trotec Speedy 300 80W, Galvo Fiber Laser 20W
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  4. #4
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    Thanks guys, will keep on experimenting
    Speedy 300 80W
    CorelDRAW x7

  5. #5
    A general rule of thumb I use for PPI is,if it cuts perfectly at a high PPI then go with it. If the material is difficult to cut, e.g.it burns or catches fire etc then i use a low PPI. I use a low PPI for wood, abs, polycarb and fibreglass. For acrylic I use a high PPI unless it is quote thick i.e. 10 to 12mm.

    Cheers
    Keith
    Universal Laser VLS6.60, Tantillus 3D printer, Electronic design
    edns Group, Mairangi Bay, Auckland, New Zealand

  6. #6
    The Universal has a really cool PPI system and it lets you take it WAY down. You can make it look like stitches. It's been a while since I did it, but it seems like you could do 10 per inch, which left a stitch like pattern, which could be useful for a number of things in vector marking, I would suppose.
    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.

  7. #7
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    Scott, if I understand what you are referring to, you can get the same effect on Trotec Job Control with the 'Link' option. (Settings>Options>Process Options>Link)
    Vector Etch Laser Cutting & Engraving
    Brisbane, QLD, Australia

    Trotec Speedy 360 120W
    Trotec Speedy 100 60W

  8. #8
    Quote Originally Posted by Andrew Holloway View Post
    Scott, if I understand what you are referring to, you can get the same effect on Trotec Job Control with the 'Link' option. (Settings>Options>Process Options>Link)
    You very well could Andrew! Link is a VERY powerful tool, one that's on my short list of video's to make now that I got things up and running on my computer again. It's not really the same as dropping the PPI on the Universal, but it could certainly work, if you told it to drop the power to zero between links.

    Good thinking!
    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.

  9. #9
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    Following on from what Scott has said -

    Because the laser is pulsed, the power is the *average power*.
    At high ppi/Hz you get lots of lower powered pulses.
    At low ppi/Hz you get fewer pulses, but each pulse has more power in it.

    For acrylic and many other plastics that melt, high ppi/Hz keeps the sides of the cut molten so that the material can be blown out by the air assist.

    For wood and difficult materials, the higher powered pulses at low ppi/Hz can vapourise the whole thickness in one hit and so make the cut edges cleaner.


    (This only applies to air-cooled lasers - the glass tube water cooled ones operate differently).
    Epilog Legend 32EX 60W

    Precision Prototypes, Romsey, UK

  10. #10
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    Quote Originally Posted by Scott Shepherd View Post
    The Universal has a really cool PPI system and it lets you take it WAY down. You can make it look like stitches. It's been a while since I did it, but it seems like you could do 10 per inch, which left a stitch like pattern, which could be useful for a number of things in vector marking, I would suppose.
    When I made our wedding invitations on my old Universal, I used that feature a lot. By "stitching" the paper, I could make fold lines that were, for all intents and purposes, invisible to the naked eye... but a slight amount of pressure applied to the area and the paper folded exactly where I wanted it to. I want to say I did something like 50-100ppi.
    Hi-Tec Designs, LLC -- Owner (and self-proclaimed LED guru )

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  11. #11
    Did someone say Wedding Invite???!!! Dan, pictures please? Would love to see what the evil genius did for his wedding!
    Jit Patel
    London UK

    30w Trotec Speedmarker CL (Galvo) with 400mm & 250mm lens
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  12. #12
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    I'm sure I posted pics here way back when... lemme see if I can find it.

    EDIT: Couldn't find the thread in my initial search, so here's a link (hope it works):
    https://www.facebook.com/photo.php?f...00000000297965
    Last edited by Dan Hintz; 03-02-2015 at 1:41 PM.
    Hi-Tec Designs, LLC -- Owner (and self-proclaimed LED guru )

    Trotec 80W Speedy 300 laser w/everything
    CAMaster Stinger CNC (25" x 36" x 5")
    USCutter 24" LaserPoint Vinyl Cutter
    Jet JWBS-18QT-3 18", 3HP bandsaw
    Robust Beauty 25"x52" wood lathe w/everything
    Jet BD-920W 9"x20" metal lathe
    Delta 18-900L 18" drill press

    Flame Polisher (ooooh, FIRE!)
    Freeware: InkScape, Paint.NET, DoubleCAD XT
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  13. #13
    Dan

    My compliments. Very nice design and work.
    Mike Null

    St. Louis Laser, Inc.

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  14. #14
    Very nice Dan. I thought you would have gone crazy with the cutting on the exterior?
    Jit Patel
    London UK

    30w Trotec Speedmarker CL (Galvo) with 400mm & 250mm lens
    80w Trotec Speedy 400 with Rotary, Vacuum Table, Cutting Lamellas, 2" & 1.5" lens, Pass through
    Oki Printing Press
    Abobe Creative Suite - Illustrator, Photoshop, InDesign.
    Vector Magic


  15. #15
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    Thanks, guys. No, didn't want to go crazy. I think we were both very happy with something simple, just like the ceremony (story for another thread). The heart cutout was a quick tweak of some clipart, and I added in the ribbon almost as an afterthought... but it held the card shut when tied, so it worked. The response cards had a pearlescent border that was also simplistic. I think my gifts to the wedding party were laser-engraved wine opener/bottle stopper kits.

    But as to the thread at hand... both the purple inner liner and the outer cardstock were stitched to make them bend at the exact spot I wanted them to. Worked like a charm.
    Hi-Tec Designs, LLC -- Owner (and self-proclaimed LED guru )

    Trotec 80W Speedy 300 laser w/everything
    CAMaster Stinger CNC (25" x 36" x 5")
    USCutter 24" LaserPoint Vinyl Cutter
    Jet JWBS-18QT-3 18", 3HP bandsaw
    Robust Beauty 25"x52" wood lathe w/everything
    Jet BD-920W 9"x20" metal lathe
    Delta 18-900L 18" drill press

    Flame Polisher (ooooh, FIRE!)
    Freeware: InkScape, Paint.NET, DoubleCAD XT
    Paidware: Wacom Intuos4 (Large), CorelDRAW X5

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