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  1. #1

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    Aug 2018
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    jerky motion on y axis

    I have finally gotten a chance to go through my router and refine a few things. I was running a 2 3/8" spoilboard surface cutter and it cuts just fine going on the x axis, but on the y axis is stutters enough to cause the gantry to wiggle just a little bit and my cutter shows it. Once it goes to cutting on the x axis it goes right back to smooth with no issues. I took the drives apart and nothing is loose, and the belts are tight. Any suggestions as to where to look? Mach 3 settings? Maybe a little wiggle is to be expected at this level of machine?

  2. #2
    Community Moderator ger21's Avatar
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    Re: jerky motion on y axis

    Almost impossible to say without seeing what it's doing, but these types of issues are most often mechanical.
    Gerry

    UCCNC 2017 Screenset
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    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

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    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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    Re: jerky motion on y axis

    Quote Originally Posted by Aerojunkie View Post
    I have finally gotten a chance to go through my router and refine a few things. I was running a 2 3/8" spoilboard surface cutter and it cuts just fine going on the x axis, but on the y axis is stutters enough to cause the gantry to wiggle just a little bit and my cutter shows it. Once it goes to cutting on the x axis it goes right back to smooth with no issues. I took the drives apart and nothing is loose, and the belts are tight. Any suggestions as to where to look? Mach 3 settings? Maybe a little wiggle is to be expected at this level of machine?

    A "little wiggle" is not to be expected. What "level of machine" do you have. Flat bar with skate bearings on the carriages? Angled rails with grooved bearings? Profile linear rails? Without knowing what machine you have, it's pretty much impossible to even guess what the problem might be. +1 regarding ger21's comments.

    Gary

  4. #4

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    Re: jerky motion on y axis

    I can understand that. Its a CNCRP Pro 5x10 with a CNC Depot ATC spindle purchased in October of last year. I will try and get some video of it tomorrow doing the same surfacing routine.

  5. #5
    Community Moderator ger21's Avatar
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    Re: jerky motion on y axis

    I'd look at the rack and pinion.
    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)

  6. #6
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    Re: jerky motion on y axis

    I can't remember which way they set it up stcok, is Y the axis with one motor or 2. If its the one with 2, improper gantry squaring can cause jerkiness, as can an issue with one of you motors/cables/driver.

  7. #7
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    Re: jerky motion on y axis

    Quote Originally Posted by Aerojunkie View Post
    I can understand that. Its a CNCRP Pro 5x10 with a CNC Depot ATC spindle purchased in October of last year. I will try and get some video of it tomorrow doing the same surfacing routine.
    Quote Originally Posted by ger21 View Post
    I'd look at the rack and pinion.
    Quote Originally Posted by Wildkard View Post
    I can't remember which way they set it up stcok, is Y the axis with one motor or 2. If its the one with 2, improper gantry squaring can cause jerkiness, as can an issue with one of you motors/cables/driver.

    Wildkard: There are 2 steppers on the Y-axis.


    Gantry squaring can be a cause, but only if you are mechanically out-of-square and try to bring the gantry into square with the homing switches. Auto square can correct minor mechanical out-of-square conditions without negative consequences, but the more that has to be corrected, the more chance of binding and other alignment related problems.

    I'd start with checking for mechanical square. The technique I recommend is similar to the one CNCRP uses, but with some differences. The page with the CNCRP routine is here: Leveling, Squaring, and Tramming Your CNC Machine | Avid CNC | CNC Router Parts. My differences: The CNCRP dimensions for the dowels is much too small. For the sake of accuracy, you want your dowel points to be as far apart as possible. They can be arranged as a square or rectangle, since your are looking at the differences in the diagonal measurements. Personally, I don't recommend trying to measure the diagonals with a framing square, tape measuring, scale or similar. You really don't care about the absolute measurement. What you really want to know is the difference in distance between the dowels. Get or make an adjustable device that will allow you to fit the device between the dowels on the diagonal. Do a quick check and determine which diagonal is the shortest length and set you adjustable device to touch the inside sides of the dowels on the short dimension. Then, leaving the adjustable device set to the short length, put it between the longer length. With one end touching a dowel, use feeler gauges or a dial indicator to measure the the difference in the short and long diagonals. The differential is 2X the amount your gantry is out-of-square (divide the differential by 2 and that's the amount you need to adjust one side of the gantry relative to the other side). This is a "measure, adjust, repeat" operation, and may take several iterations to get it dead on.

    Once your gantry is square, you need to ensure that your limit switches are properly adjusted. No sense in getting the gantry mechanically square, only to have the homing switches pull the gantry out-of-square when homing.

    Another possible cause is has to do with how much you've tightened your tensioning springs on your Y-axis drives. If too loose, the pinion can lose full engagement in the rack and cause odd movement. CNCRP recommends tightening the tensioning spring 3 full turns after finger tight. A good starting point, but not the last word on that will work best. I suggesting tightening a quarter turn tighter and see what happens. You can make incremental changes up to maybe 4 turns total. If that doesn't solve the problem, you may need to look elsewhere. Tensioning has been a documented issue here on the Zone. Keep in mind that if the spring is too tight, it will cause premature wear. It's a balance between too tight and not tight enough.

    I recommend squaring the gantry as a first step. If the gantry is out-of-square, it can and will throw of other areas and send you wild goose chases.

    Gary

  8. #8

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    Here are a few pics of the surface after running a small fly cut file. The ridges are all when cutting in the y direction, the x direction there is no problem. You can feel the gantry shake like its starting and stopping constantly.

  9. #9
    Community Moderator ger21's Avatar
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    Re: jerky motion on y axis

    Does the gantry move smoothly when the power is off? This is almost certainly a mechanical issue.
    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)

  10. #10

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    Re: jerky motion on y axis

    I can run the file again with the spindle off (cutter removed) and report back. I have a video of it cutting but cant get it to upload here. Dropbox link I guess?

  11. #11
    Community Moderator ger21's Avatar
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    Re: jerky motion on y axis

    No, not with the spindle off. With the steppers off, can you manually push the gantry, and does it move smooth?
    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)

  12. #12

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    Aug 2018
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    Re: jerky motion on y axis

    I understand now. I unplugged the cables and moved the gantry back and forth. You can feel a notchiness in the y axis movement, but I can also feel the same thing in the x direction as well. Both directions were really stiff to move with the gear/steppers engaged. Also backed off the springs on both directions and they move really smooth without the gears/steppers engaged, I wanted to make sure that wasn't binding.

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