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Thread: Excessive Jerking with tight font serifs

  1. #1
    Join Date
    Nov 2016
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    New Mexico
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    Default Excessive Jerking with tight font serifs

    Our Shopbot desktop cuts fonts of any kind and shape well. However, with tight font serifs, our cutter head is jerking the machine trying to square up the round serif in some fonts. It is not a smooth motion, even though we have slowed down the settings in the VR sheet.

    Here's the shopbot report to us:

    The tool moving fast through those different movements is all mixed in with the cutting speed, nature of each of the moves and what ramps are being employed based on those moves. The VR sheet can change this a little, but based on what you are doing there won't be a change.

    Maybe someone has experience with this issue and knows something? A fix?

    We have slowed down the speed in VCarve to super slow with those fonts with tight serifs. Even then, we see our cutter head jerking fast trying to square a serif.

    Thanks in advance for advice with this one.

    (Sorry... This should be in the Troubleshooting section. My fault.)
    Last edited by woodshop; 03-14-2017 at 09:38 AM.
    Dave B
    New Mexico

  2. #2
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    568

    Default

    Dave, can you post some pictures of what you are getting? While I don't have your type of machine, I think most everyone likes to see other people's V-carving. And for those who are experts, the pictures are valuable for diagnostic purposes.
    Good luck, Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 8.5, Rhino 5

  3. #3
    Join Date
    Dec 2000
    Location
    Thorp, WI
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    2,443

    Default

    When v-carving small serifs, the toolpath at the end of each of them is a short quick up/out and back down/in motion that can cause 'jiggle' in the machine. This is more evident on a larger tool, but can still be abrupt enough on a desktop to impart some vibration. Adjusting just the move ramp speed in VR will not alleviate this. When I do small to medium v-carving on my PRS4896, I load a completely different set of ramps that make those spots smoother and sort of mushy in motion.

    Along with adjusting the move ramp speed a bit, try adjusting the move ramp rate, 3D ramp threshold, and slow corner speed. Attached is what I run, but it may not be optimal for a desktop, so use it as a template and find what works best for you.

    Issue a 'US' to save your current/default settings before changing the ramp values and that way you'll have a set of 'Standard' ramps to revert to. I take that saved file and delete all but the VR line and save it as a custom cut file with the name of the intended ramp settings within. That way I can load it or any other ramping scheme (3D, V-Carving, or Standard) as needed.

    Also, use the same feedrate for the Z as you do for XY. This keeps the XY from having to slow down for the Z axis and helps keep a more even flow throughout the cut.

    Attached Images Attached Images
    Scott

    If guns kill people, I guess pencils misspell words, cars drive drunk and spoons make people fat.

    "Those who hammer their guns into plows, will plow for those who do not" - Thomas Jefferson


  4. #4
    Join Date
    Nov 2016
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    New Mexico
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    Default

    Ok and thanks. Will try that today.
    Chucks question: My web site shows it all: http://zaneblackwoodshop.com
    Dave B
    New Mexico

  5. #5
    Join Date
    Nov 2016
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    New Mexico
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    Default

    Wonderful. Great solution to our problem. Thanks so much!

    We are wondering why the shopbot service guys did not know this.
    Dave B
    New Mexico

  6. #6
    Join Date
    Jan 2004
    Location
    Norman, Ok
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    3,040

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    Dave,

    Let me complement you on some beautiful work. I'd like to see even more of your sign.

    Scott did an excellent job with his description. The reason the tech fellows at SB didn't give you assistance like that is they don't have the day to day experience. At some point this becomes much like a dance. Which you means to get the most out of the equipment requires tweeking. That's where craftsmanship comes into play.

    Happy Routing,

    Joe

  7. #7
    Join Date
    Nov 2016
    Location
    New Mexico
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    Nice to hear from you Joe.
    Yes, Scott is my new "GO-TO" guy. Many others here are also of that rank in my book.
    We now understand the "Dance" and greatly appreciate the time you took to address this issue.
    We have lost confidence in the techs at SB.
    Maybe this forum could have a new section on "Tweeking."
    Thanks for you compliment. Any chance we can talk by phone?
    Dave B
    New Mexico

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