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  1. #1
    Join Date
    Aug 2018
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    59

    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
    Join Date
    Mar 2003
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    35538

    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

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

  3. #3
    Join Date
    Apr 2016
    Posts
    841

    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
    Join Date
    Aug 2018
    Posts
    59

    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
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    Mar 2003
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    35538

    Re: jerky motion on y axis

    I'd look at the rack and pinion.
    Gerry

    UCCNC 2017 Screenset
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    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
    Join Date
    Nov 2015
    Posts
    31

    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
    Join Date
    Apr 2016
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    841

    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
    Join Date
    Aug 2018
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    59
    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
    Join Date
    Mar 2003
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    35538

    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
    Join Date
    Aug 2018
    Posts
    59

    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
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    Mar 2003
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    35538

    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
    Join Date
    Aug 2018
    Posts
    59

    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.

  13. #13
    Join Date
    Aug 2018
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    59

    Re: jerky motion on y axis

    Not sure how this will work, but here is a link to a video of the router running the file.



    https://drive.google.com/open?id=14W...q9Bw4iIk2K6JQ8

  14. #14
    Join Date
    Apr 2016
    Posts
    841

    Re: jerky motion on y axis

    Quote Originally Posted by Aerojunkie View Post
    Not sure how this will work, but here is a link to a video of the router running the file.



    https://drive.google.com/open?id=14W...q9Bw4iIk2K6JQ8


    Wow! That's really bad. I've never seen anything like it. How's your spindle tram? I'm not at all certain that being out of tram could cause what we're seeing, but I suppose it might - if it's out of adjustment enough. Do you have the CNCRP tramming plate?

    Also, is this something that has just cropped up after hours of trouble-free use, or are you setting up your machine from new?

    It looks like you are using a cutter with carbide inserts. Have you used this cutter before, and if so, did it cut cleanly? It suppose there could be something wrong with it, although that wouldn't be my first guess. Have you tried a different cutter, like a 1/2" 2-flute bit? A 1-1/2" or so bottom cleaning router bit would probably be even better, if you have one.

    Gary

  15. #15
    Join Date
    Aug 2018
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    59
    Here are a few pics of my tramming setup and measurements. The 4 pictures are going clockwise around a circle without moving the spindle or adjusting anything. The last pic is of the 10"circle that is the distance covered from one side to the other. Its not perfect, but I thought it was pretty good.

  16. #16
    Join Date
    Aug 2018
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    59

    Re: jerky motion on y axis

    I haven't used my machine much, (this is my 2nd job/hobby) but I have been using 1/4" compression and down cuts bits so far and they seemed to cut ok. The only other machines I have been around were $100k+ at woodworking shows and I knew this wasnt at that level so I was thinking a less than perfect cut was to be expected. Until now I was using a 1/2" straight bit to do the same thing, that takes forever to do. I cant really say when this started, or if it was doing it at a lesser extent from the beginning. Here is the cutter that I have.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

  17. #17
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    Mar 2003
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    35538

    Re: jerky motion on y axis

    I can't watch the video right now, as I have a poor internet connection.

    If those milling marks are all the way down the table, then it sure looks like a tram issue, unless the machine is actually shaking all the way down from end to end?

    If it is, then I still think it's a rack and pinion 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)

  18. #18
    Join Date
    Apr 2016
    Posts
    841

    Re: jerky motion on y axis

    Quote Originally Posted by ger21 View Post
    I can't watch the video right now, as I have a poor internet connection.

    If those milling marks are all the way down the table, then it sure looks like a tram issue, unless the machine is actually shaking all the way down from end to end?

    If it is, then I still think it's a rack and pinion issue.

    Gerry,

    The marks do, in fact, go all the way down from end to end. The video is worth looking at, if you get the chance. Very ugly milling marks. While a tram issue occurred to me, and the tram is off way more than I would tolerate (see pics above), I question whether it is off enough to cause what we're seeing in this case. If I recall correctly, my first machine was off more than this one before I trammed it, and it didn't have anything like these mill marks. The 'axis stuttering' and 'gantry wiggling' sure sounds like a rack & pinion issue, but what is the underlying cause? Maybe the gantry is far enough out-of-square to put the axis in a bind, and cause lost steps. Or, maybe the tensioning screw is too loose, allowing the pinion to hop up and down? Maybe a combination?


    Quote Originally Posted by Aerojunkie View Post
    I haven't used my machine much, (this is my 2nd job/hobby) but I have been using 1/4" compression and down cuts bits so far and they seemed to cut ok. The only other machines I have been around were $100k+ at woodworking shows and I knew this wasnt at that level so I was thinking a less than perfect cut was to be expected. Until now I was using a 1/2" straight bit to do the same thing, that takes forever to do. I cant really say when this started, or if it was doing it at a lesser extent from the beginning. Here is the cutter that I have.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    You may be surprised to hear that these kit machines can actually cut very well. If they are adjusted correctly, they cut well enough that you probably wouldn't be able to see the difference in a project between the kit and a $100K+ machine - at least when cutting wood products. You should look at some of the pieces depicted here on the Zone and on other sites cut on hobby machines. My first machine was similar to the CNCRP standard version (skate bearings and metal plates for them to ride on. Pretty clunky. Still, after taking a lot of time tuning and adjusting, I'd put the pieces I cut up against those cut on industrial machines. Mine just took longer to cut. Also, my machine, which was a 4' x 4', was way more limited. Long story short, if your machine is not cutting well, there is probably something wrong with the machine, the cutter is bad or the wrong one, or it's operator error.

    I leveled my spoilboard once with a 1/2" bit. Never again, and mine was/is only a 4' x 4'. I've known people who used a 1/4" bit. I'm sure it's comparable to the excitement one would expect from watching paint dry.

    I have the same surfacing bit you are using. I've had no problems with mine. If it was the problem, I'd expect to see milling marks both the X and Y directions. Way low on my list of suspects.


    Quote Originally Posted by Aerojunkie View Post
    Here are a few pics of my tramming setup and measurements. The 4 pictures are going clockwise around a circle without moving the spindle or adjusting anything. The last pic is of the 10"circle that is the distance covered from one side to the other. Its not perfect, but I thought it was pretty good.
    I recommend improving your tram. You'll get nicer cuts.



    Please refer back to my comments on gantry squaring, drive tensioning, etc. You've nicely doc'd what you're seeing, and addressed tram, but have not addressed the other issues that could account for your problem. Without more information, I am unable to offer much additional specific input.

    Gary

  19. #19
    Join Date
    Feb 2005
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    829

    Re: jerky motion on y axis

    Have you reached out to AvidCNC/CNCRouterParts?

  20. #20
    Join Date
    Dec 2003
    Posts
    1206

    Re: jerky motion on y axis

    I watched the video and two things come to mind.Were you using the same collet for the spoilboard skim that you used when tramming the machine?If not ,it might be worth trying a new collet in case dirt or wear have reduced the accuracy or concentricity of the one used for skimming.The other issue that might be causing the uneven cut could be resonance of the Z axis and the gantry and if it is occurring it will appear worse with a flycutter simply because of the tips being further from the spindle axis.

    I can't see an easy way of isolating the cause.Is there a way to temporarily mount a sturdy piece of steel carrying a dial gauge to the gantry while the cut is running?Any flutter of the needle could point to a little play in the Z axis or spring in the gantry cross beam.

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