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  1. #1
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    Mar 2011
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    53

    Acceleration - Is there a sweet spot?

    Hello Everyone!

    Been away for a while just getting used to working with this new machine (CRP PRO 4x4). In general, it's running GREAT!

    Did some test cuts, cut a few things for friends, experimented with different settings and materials, etc.

    It has been very helpful reading the various posts. I've had a lot of my questions answered just by following others' footsteps.

    I've been experimenting with the acceleration settings of my X & Y. Seems that somewhere between 20 and 30 Inch/Min/Min gets the best results while cutting wood at 100-160 Inch/Min. Went down as low as 10, but found that I was getting corners rounded off that should have been square.

    Can I get a few opinions from you folks on your acceleration settings AND why/how you came to those conclusions? Do you guys have a tuning method to find a sweet spot?

    Thanks, Bernie

  2. #2
    Community Moderator ger21's Avatar
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    Re: Acceleration - Is there a sweet spot?

    Generally, the faster the acceleration, the better. Faster accel can greatly reduce cycle times, especially with 3D carving.
    One big exception here, is when you reach the limits of your machine's rigidity. Mach3's linear accel and decel can start to get rather violent with really high acceleration settings. Quick directions changes can cause the machine to flex and shake, which will show up as poor cuts.
    This usually isn't an issue, though, as most homebuilt machines don't have enough power to accelerate that fast.

    The typical method of setting acceleration is to pick a target velocity that you want to cut at, then start raising the acceleration, and testing to see if you lose any steps. If you don't lose steps, raise the accel, and test again. Repeat until you start to see lost steps or motors stalling.
    At that point, take the last good setting, and reduce it by 15%-25%, for a safety margin.

    The rounded corner issues can be taken care of by adjusting your CV settings. The best "general" settings are these. Turn CV mode on, but turn off all the CV options. Both CV Distance and CV Feedrate on the settings page, and all the CV options in General Config.
    Then turn ON "Stop CV on Angles>", and set it to 89. This will prevent the rounding of 90° (and more acute) corners regardless of the acceleration settings. Depending on what you're doing, you may want to set it even lower than 89.

    Of course, keep in mind what I said earlier. If a lower acceleration gives better cuts, then by all means lower it. Every machine is different, and the machine will ultimately dictate how much accel it can tolerate.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  3. #3
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    53

    Re: Acceleration - Is there a sweet spot?

    Gerry,

    Thanks for taking the time for that very clear explanation.

    This stuff is actually starting to make sense and sink in. I guess putting in the hours with the machine, experimenting and testing, is the only way to REALLY get the feel for this technology (along with some machinist's trade skills).

    So, this method of yours for finding and setting acceleration can be done via "air-cutting", right? Or, is it important to have a cutter actually hitting material during quick direction changes?

    I'll do some more experimenting per your suggestions and get closer to the fine tuning that I'm looking for.

    -- Bernie

  4. #4
    Community Moderator ger21's Avatar
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    Mar 2003
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    34607

    Re: Acceleration - Is there a sweet spot?

    Yes, air cutting is fine.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

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