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    Question imperfect circles

    Hi all! Keith here! machine is coming along great and cutting pretty well! have a small issue, though. As the post title suggests, I am cutting imperfect circles. I am using Mach 3 and have nema 23 steppers. any thoughts?

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    Default Re: imperfect circles

    How about you tell us what is imperfect about them. The possibilities are endless.



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    Default Re: imperfect circles

    how about i do that!?!?! silly me!

    Attached Thumbnails Attached Thumbnails imperfect circles-img_20170221_222757756-jpg   imperfect circles-img_20170221_222750739-jpg  


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    Default Re: imperfect circles

    aaaand just off the machine 3 minutes ago!

    Attached Thumbnails Attached Thumbnails imperfect circles-img_20170221_225659886-jpg   imperfect circles-img_20170221_225717203-jpg  


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    Default Re: imperfect circles

    they look pretty consistent in being rounded off squares! i just dont know why? the machine is solid in all axes.



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    Default Re: imperfect circles

    Quote Originally Posted by kebuttke View Post
    they look pretty consistent in being rounded off squares! i just dont know why? the machine is solid in all axes.
    Solid may be but certainly looks misaligned. Of course, it may also be some other issue, like missing steps on one axis, but I suspect it is a mechanical issue.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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    Default Re: imperfect circles

    Out of curiosity are your X and Y motors identical? If so, are they set up with the identical parameters in Mach?

    David
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    Default Re: imperfect circles

    It is likely caused by either incorrect steps per setting on an axis or loss of steps. Check all pulleys, couplers etc to ensure nothing is loose... then check them again. 90% of the time something loose is the culprit behind lost steps. If you are still loosing steps and everything appears tight and the issue isn't mechanical, you may be loosing steps because an axis is binding or motor settings (including your acceleration speeds) are too high/fast. If it's not a mechanical issue, slow down your motor speeds and accel by half or more a make a couple test cuts. There are some other settings in Mach3 that can cause lost steps or issues but unlikely unless you have been playing around with all the settings. If you can't find anything after checking the above, save your machine profile and go through the Mach manual and start with default router settings (other than your ports and pins).
    Good luck!



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    Quote Originally Posted by difalkner View Post
    Out of curiosity are your X and Y motors identical? If so, are they set up with the identical parameters in Mach?
    They are identical. As far as settings for the slave motor, I will check it tonight.



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    Quote Originally Posted by coherent View Post
    It is likely caused by either incorrect steps per setting on an axis or loss of steps. Check all pulleys, couplers etc to ensure nothing is loose... then check them again. 90% of the time something loose is the culprit behind lost steps. If you are still loosing steps and everything appears tight and the issue isn't mechanical, you may be loosing steps because an axis is binding or motor settings (including your acceleration speeds) are too high/fast. If it's not a mechanical issue, slow down your motor speeds and accel by half or more a make a couple test cuts. There are some other settings in Mach3 that can cause lost steps or issues but unlikely unless you have been playing around with all the settings. If you can't find anything after checking the above, save your machine profile and go through the Mach manual and start with default router settings (other than your ports and pins).
    Good luck!
    I don't believe I'm losing steps, or at least I can't tell. As far as the acceleration, I have actually increased it from very light cuts. After reading and thinking and thinking and reading, I realized I haven't done much to address backlash.



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    Default Re: imperfect circles

    i may have found my issue with the inability to reduce backlash to an acceptable level.

    - - - Updated - - -

    and a few more

    Attached Thumbnails Attached Thumbnails imperfect circles-10-jpg   imperfect circles-2-png   imperfect circles-11-png   imperfect circles-1-png  

    imperfect circles-3-png   imperfect circles-4-png   imperfect circles-5-png   imperfect circles-6-png  

    imperfect circles-7-png   imperfect circles-8-png   imperfect circles-9-png   imperfect circles-12-png  

    imperfect circles-13-png   imperfect circles-14-png   imperfect circles-15-png   imperfect circles-16-png  



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    Default Re: imperfect circles

    there is no way, with this drive, to reduce the axial play to an acceptable level. further, the pinion gear has at least .005 play radially. add that to the axial play on the thrust bearing and the sealed bearing inside of it, and there yo have it. .025" backlash. they say imitation is the sincerest form of flattery. in this case, im not so sure. i dont think cncrp is so sure, either. i was also unaware of htd belts, while okay, are not what would be expected of a several thousand dollar machine. the rest of the machine is nice. the gantry rides smooth as butter. the y axis slides back and forth on the gantry nice as can be. the cncrouterparts.com electronics package is sweet! however, misrepresentations are made about this machine, what it is capable of out the gate, and the level of customer service that comes with it. "i dont know" and "im not sure" are out of line for the owner of a company making bold claims as to the utility and accuracy of their product. Nate, if you read this, these drives are less than capable of the ACCURACY claimed. for this portion of the matter to be satisfied, please contact me through email.



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    Default Re: imperfect circles

    If you're not loosing steps then I think you might still have a software issue. How the post processor handles the gcode output and most specifically how it is cutting circles, arcs and radii can cause problems. You said you were using Mach3 but what software you draw the part with and the post processor you use can make a difference. You can always try writing simple gcode in notepad to cut a basic circle and run it to test the results. Research how best to write the code for circles and arc segments etc to run with Mach3 if you aren't familiar with writing gcode.

    Having someone run your file/code may not even identify the problem because as I stated previously there are also Mach3 settings that can effect how arcs and circles are cut (even if the post file/gcode is correct) and cause errors. How do you have your Mach system set for IJ mode on circles? It ought to be for relative IJ values. The setting is on the Config->General page, near the center of the second column. There are other possibilities such as CV and Stop CV on angle settings, backlash incorrect settings, and others. I'm not disputing the axial play you mention, but the photos you posted show issues which appear to well exceed ,025 of backlash. While it is impossible to eliminate all backlash, CNC routers and plasma cutter projects are by nature much less critical than a milling operation where a couple of thous of spindle runout can make a huge difference. I know how frustrating such issues can be but hang in there because the bright side is that the culprit is usually something very simple... once you figure out the cause. That's the hard part.



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    Default Re: imperfect circles

    I was going to suggest that looks like classic backlash issue. You have rounded squares that are consistent in the X and Y axis. Mach has a backlash compensation in the drop-down menus, but best to address the significant mechanical issue.

    Rebuilding my Bridgeport Boss3...


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    Default Re: imperfect circles

    Keith, I'm trying to understand the series of photos you posted with the pinion assembly. It seems to me that axial play wouldn't create backlash, and that radial play would just be overcome with the tensioner?

    I would do a direct measurement with an indicator in the spindle against a piece of steel to measure actual backlash.

    I had to re-indicate a hole, and with an indicator I didn't see more than a thousandth or so....nothing to worry about.

    Ward



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    Quote Originally Posted by sybilsurf View Post
    Keith, I'm trying to understand the series of photos you posted with the pinion assembly. It seems to me that axial play wouldn't create backlash, and that radial play would just be overcome with the tensioner?

    I would do a direct measurement with an indicator in the spindle against a piece of steel to measure actual backlash.

    I had to re-indicate a hole, and with an indicator I didn't see more than a thousandth or so....nothing to worry about.

    Ward
    If the arm is able to walk, it changes the engagement of the teeth with the rack. Doing that in both directions causes tooth wear, which I have, and the arm moving inward and outward changes the angle of the torque applied to the rack as well. I have observed this using .001" step on jog. Additionally, the reduction wheel, which you can see in one of he pictures, has play in it at the woodruff key. I am not a CNC mechanic, but diagnosing play in unfamiliar mechanical systems is somewhat the norm in general aviation. I have confidence that the cncrp drives will resolve this issue.



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    Quote Originally Posted by kebuttke View Post
    If the arm is able to walk, it changes the engagement of the teeth with the rack. Doing that in both directions causes tooth wear, which I have, and the arm moving inward and outward changes the angle of the torque applied to the rack as well. I have observed this using .001" step on jog. Additionally, the reduction wheel, which you can see in one of he pictures, has play in it at the woodruff key. I am not a CNC mechanic, but diagnosing play in unfamiliar mechanical systems is somewhat the norm in general aviation. I have confidence that the cncrp drives will resolve this issue.
    For everyone that's looking at this I saw a disassembly video of this pinion drive. On the cncrouterparts drives everything is press fit.

    With this knock off drive, Keith was able to just push all of the bearings and pinion gear out with just his thumb.

    There is something seriously wrong with this drive. Tolerances aren't even close to spec.


    Just the pinion itself is slopping around back and forth in the aluminum pulley. Again. He was able to slide to bearing and pinion out with his thumb.

    Not to metion these gears require gt series belts. Not the supplied htd series.



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    Quote Originally Posted by coherent View Post
    If you're not loosing steps then I think you might still have a software issue. How the post processor handles the gcode output and most specifically how it is cutting circles, arcs and radii can cause problems. You said you were using Mach3 but what software you draw the part with and the post processor you use can make a difference. You can always try writing simple gcode in notepad to cut a basic circle and run it to test the results. Research how best to write the code for circles and arc segments etc to run with Mach3 if you aren't familiar with writing gcode.

    Having someone run your file/code may not even identify the problem because as I stated previously there are also Mach3 settings that can effect how arcs and circles are cut (even if the post file/gcode is correct) and cause errors. How do you have your Mach system set for IJ mode on circles? It ought to be for relative IJ values. The setting is on the Config->General page, near the center of the second column. There are other possibilities such as CV and Stop CV on angle settings, backlash incorrect settings, and others. I'm not disputing the axial play you mention, but the photos you posted show issues which appear to well exceed ,025 of backlash. While it is impossible to eliminate all backlash, CNC routers and plasma cutter projects are by nature much less critical than a milling operation where a couple of thous of spindle runout can make a huge difference. I know how frustrating such issues can be but hang in there because the bright side is that the culprit is usually something very simple... once you figure out the cause. That's the hard part.
    Do you think the XML file Nate has for his Saturn 4x4 might help on this situation?



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    Default Re: imperfect circles

    kebuttke... It couldn't hurt to try Nate's file and test it out. I'm not discounting it being a mechanical issue but was hoping to point out other other possibilities that can cause such issues... I've seen incorrect Mach3 settings screw things up much worse than your issues.
    I've been playing with CNC machines since about 2002 and Mach since it was initially released so my previous input and comments are based on my experience with my previous builds and Mach... not these specific Saturn machines.
    I must admit that Ericclinedinst's comments got me thinking and a bit troubled. My Saturn machine (delivered in Jan 2017) had a mix of Gates and HTD belts... I ordered some extra belts from the same place you (Keith) ordered yours. I've haven't had any broken belts, but simply wanted spares on hand. Lower quality belts aren't a major concern but lower quality parts in the pinion assembly are. There is always the possibility of simply a bad part or assembly which is not the norm from any manufacturer.
    I'm still in the process of building and finalizing my machine because I'm waiting on a couple parts for a floating head assembly and the plasma water table to be completed. As a side note, I was on the interstate driving in Jan and was struck and ran off the freeway by a driver who lost control of his vehicle, hit me and my vehicle rolled 3 times. I was lucky and my wife and I walked away, but priorities changed and I'm still a bit sore and moving slow. So, basically I'm behind where I had hoped to be as far as my machine build and haven't had a chance to run it actually cutting or check it's backlash much less check the pinion drives for play. I'll definitely need to take a closer look. Some input or comments from Nate or someone else at Fineline would be appreciated and I think in order. I'm now more than a little curious how the specified accuracy quotes listed for these machines was achieved/tested and if the exact same parts and build tolerances are the ones used for our machine builds and all sales of the Saturns. I really don't mean or want to raise doubts as to the machine's quality and from what I've seen so far it's very well made and it's quality seems great, but then again some assurance and information from Fineline could always help.

    Last edited by coherent; 02-24-2017 at 09:15 PM.


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    Quote Originally Posted by coherent View Post
    My machine had a mix of Gates and HTD belts... I ordered some extra belts from the same place Keith ordered his. I'm still in the process of building and finalizing my machine so haven't had a chance to check it's backlash or check the pinion drives for play. I think I need to take a closer look. Some input or comments from Nate or someone else at Fineline would definitely be appreciated and I think in order.


    Yeah. Htd belts are not good on gt gears. You can do it but that's such a sloppy mesh between the two. Which WILL create backlash. Htd belts will also have the teeth shear right off if you hit something hard. Then there's the shredding that Keith has already experienced....

    Sounds like to me someone is cheaping out in the wrong areas


    Here's a somewhat decent article to check out on the difference. https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.sdp-si.com/D265/PDF/D265T003.pdf&ved=0ahUKEwiO1aiIkarSAhUDMSYKHboqBrwQ FggkMAM&usg=AFQjCNExw16y1GREYCKF_JIDYYvqsN3j2w

    Part of the issue is that the htd belts don't fully full the gt profile. Causing backlash each time there's a direction change.



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