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  1. #1

    I seem to be having a problem when I cut curves on my machine. Im running it with Linuxcnc. It doesn't have any problems when cutting circles. It is just when there is a curve that is made with multiple circle radius's.
    This isn't a mechanical problem but a software/computer speed problem. When it is cutting a curve the machine accelerates and decelerates because the computer cant spew out the information fast enough(im guessing this is the problem).

    Has anyone came across this problem before and found any fixes? I've heard that disabling the internet card frees a lot of speed up on the computer. Maybe adding more ram might help?

    Any info would be really helpful as in the near future im going to be cutting out some big molds out of foam for fibreglass. The molds are for a fsae car hence are heavily curved, none being a nice simple circle.


  2. #2
    Hi from this CNC newbie. It will be a while before the UK wakes, so meantime I'll pass on what I think I've read. . .
    The recommendation seems to be to run Mach3 or equivalent off a dedicated desktop PC that is as close to a raw vanilla O/S as possible, to avoid the potential for problems, which problems may be similar to what you are suspecting.
    Even old laptops that have a parallel port tend to be avoided due to the complications introduced by special laptop software such as power-saving settings. I understand that using a device such as an ESS (Ethernet Smooth Stepper) can dramatically improve the reliability of the PC-Machine interface and think that ESS is favoured by JAZZ. I think Jonathon is a Linux fan.
    In short I would try deactivating whatever you can and see what difference it makes.

  3. #3
    It will probably be down to CV mode. CV can be set to either Exact stop G61 or Constant Velocity G64. Check the G-code to see if it contains G61.

    G61 will pause at the end point of each Arc or line segmant that make up the curve but follow closely the shape.

    G64 keeps a constant feed by blending one segmant into the other, when the first segmant starts to decelerate at it's end point the next segmant starts to accelerate and the moves get blended together. This can give the affect of larger than required radius in square corners as the control try's to maintain commanded feed and acceleration while going around the bend but the control says hold on I can't go that fast around that bend but as to maintain the speed so it changes the radius to one it can go around at that speed.!! The affect of the radius is inversely proportional to acceleration. For this reason G64 as P & Q parameters to help with path deviation.

    Mostly you'll cut in G64 mode as it gives smoother operation around corners. G61 is ok if your doing lots of point to point work but can be very jerky in corners, esp when the corner is made up of lots of line segments like lots of Cam software like to spit out. You can instantly tell when machines set in G61 because it shakes the machine in corners.

    If your G-code doesn't contain G61 then type G64 into the MDI before running same code and see if it runs differant. If it does then chances are Linux default parameters are set to G64.? I don't use Linux cnc so can't help you here.

    One thing I do know thou is a very experienced CNC user who migrated to linux cnc came back to Mach3 because among other things the CV in Linux cnc was rubbish.!! . . . . It could be the same issues your experiencing.?
    Last edited by JAZZCNC; 06-04-2014 at 08:24 AM.

  4. #4
    If the problem were with Mach3 I'd suggest the official Mach3 support forum as the support is excellent both from general members and the very experienced admin staff, the response to requests for assistance there is outstanding, presumably Linux CNC too has a support forum, have you asked there?

  5. #5
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Has been a member for 9-10 years. Has a total post count of 2,148. Received thanks 236 times, giving thanks to others 5 times.
    There's a new LinuxCNC projectory planner being written, as the existing one has issues in some key areas.
    Ironically the discussion about it was on the Mach yahoo group, as somebody had swapped back to Mach3 to get better performance -
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  6. #6
    When the machine follows a curved line, both axes are accelerating. If the acceleration setting in the motor tuning is too low, the machine will therefore have to slow down. So check what your X and Y accelerations are set to.

    Edit: The above is probably irrelevant, didn't spot that you said it was fine with circles.
    Last edited by Jonathan; 06-04-2014 at 11:07 AM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  7. #7
    Quote Originally Posted by m_c View Post
    There's a new LinuxCNC projectory planner being written, as the existing one has issues in some key areas.
    Ironically the discussion about it was on the Mach yahoo group, as somebody had swapped back to Mach3 to get better performance -
    Surprise surprise eh.!! . . . . . So Those returning to Mach complaining about these " Key Areas" are not just trouble causing Geek haters.!

  8. #8
    Thanks for all these responses! Jazz will have to read your post again and will get back to you. Never had any problems with rounded square corners. Havent got any code on me now.

    I think its best if I upload a youtube vid. Ill post it here. Should be here in less than an hour.
    Last edited by swisscheese; 06-04-2014 at 11:55 AM.

  9. #9
    Read this post and the few that follow it. You apparently need to specify Q0 when using G64 mode, or you'll get the results you're seeing. A lot of people have complained about the CV mode in LinuxCNC for a long time, and part of the issue is apparently due to a lack of documentation.

    New Trajectory Planner - Testers/programs wanted
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  10. #10
    I just remembered ive already uploaded a vid that kind of shows it. Here it is

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