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Simple Z-Axis Enhancement

Discussion in 'Troubleshooting' started by JJHawg, Oct 23, 2013.

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  1. JJHawg

    JJHawg New Member

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    I was getting some very slight waves when printing talls items, and when I saw that the carriage is just sitting on two small nuts on the z-axis lead screws, I decided to try a couple little tweaks... These are not approved by the factory, but shouldn't void the warrenty... ;-)

    The first thing I did was replace the 5/16-18 nuts with coupling nuts that are almost 1" long; I used McMaster-Carr 90264A445 (http://www.mcmaster.com/#catalog/119/3178/=p2jcqm). These have a little less free-play than the little nuts. Because of the extra nut length I lubricated the screw with some liquid graphite stuff, like for locks.

    The longer nut created a way hold the carriage more securely to the nut. I printed a little retainer that is installed underneath the nut, and then wrapped a rubber band around the carriage. In the attached picture I am pulling the nut holder down so you can see the bottom of the nut.

    I did the mod by tying the carriage to the top of the unit, and removing the all-thread, and fitting the new nut and retainer. While the rod was out I also wrapped a narrow, 2" long strip of masking tape around the base of the rod to help center it in the coupling.

    After doing this tweak the sides are much more consistent, but I had also made some slicer adjustments, so I can't necessarily attribute 100% of the improvement to the new arrangement...

    I also attached the stl file for the nut holder; it isn't anything fantastic, but it works.
     

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    #1 JJHawg, Oct 23, 2013
  2. tesseract

    tesseract Moderator
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    you should take the retainer off the nut is supposed to be free floating it prevents the bed from being damaged also make sure there is enough free room under the bottom of the bolt so that it can move freely if the z stop setting does not activate due to a close setting.

    There is actually nothing to retain as well if the nut moves to low and out of the fitted position the rod simply spins and the bed is not forced to lower more.

    I would take a careful look at this mod and make sure you understand why the nut is setup to act the way it does.

    The major stability of the z axis does not come from the threaded rod that is simply used as a mechanism for lifting and lowering the Z axis. The main stability is derived from the sleeve bearings moving on the smooth rods.

    A mod to stabilize the smooth z rods will probably add more to the stabilization you are looking for than on the threaded z rod.
     
    #2 tesseract, Oct 24, 2013
  3. JJHawg

    JJHawg New Member

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    Thanks for your comments; I share your concerns. Anyone considering this mod needs to read the previous post...

    I think that the variations that I was seeing in layer width were caused by slight variations in layer height, which is translated to width by how much material is squeezed under the nozzle.

    The large nuts minimize thread play and the rubber bands simply prevent the carriage from free-floating on the nuts, but don't prevent it from lifting if necessary...
     
    #3 JJHawg, Oct 24, 2013
  4. tesseract

    tesseract Moderator
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    I do understand that but I am concerned about the length of the rod covered by the retainer part is all. Without seeing it in action during a fail it is hard to make sure everything clears everything else.

    thinking about your idea as to the issues you are seeing...remember that gravit y will hold it down onto the top most thread regardless of it moving up or down until the nozzle comes into contact with something then it will cause the assembly to lift and I think this would be more likely than how threads are making contact.

    You may be seeing a bed leveling issue the glass itself will be flat but the rails it is attached to may have some issues.

    I know in my own experience before I got the bed levelers installed(my own simple mod)--- but not plugging in anyway LOL--- if I were to do a print I would see a wide varaition in the layer width as the nozzle moved from area to area but no I have the bed itself leveled to within about just over 70 microns in each corner, all my layers seem VERY consistant once flow is going smoothly.

    In fact when I help people I focus on getting that skirt and first layer to be very uniform
    MY basic printing rule
    Look at the skirt if it is bad stop the print adjust and restart if it is good continue

    and I use this pic to visualize a good skirt and first layers first layer example.jpg this actually has some bad things also but they are because Iw as actually lifting the z axis while printing with may hand just to see the affect but it is a good instructional reference

    That is a skirt and a brim and they are very consistent slightly flattened and solid

    LOL this was taken a while back when my bed had not been leveled so this only happened in the center of the bed but now it happens pretty much anywhere on my bed
     
    #4 tesseract, Oct 24, 2013
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