Z-axis instability is one of the most common problems in DLP/MSLA (LCD) 3D printing. The reason of z-axis instability  is usually  

due to the assembly of  z-axis slider, or wear or looseness caused by repeated up and down mechanical  movement.  When the  z-axis  

instability occurs,  the forming platform  will not fall to the same  position  accurately  during  each return of the up and down motion, 

which will cause undesirable printing lines and even layer offset between layers.

       First,  consider  more  advanced  mechanical components.  A common solution to z-axis instability  is  to replace the original slider 

with  two axis linear  guideway  system.   The  biaxial  guide makes  the forming platform more stable,  does  not  need to  be adjusted  

repeatedly over time, helps to maintain stability in motion, and ensures that the forming platform  does not offset during  the  printing  

process,  ensures  that  they  maintain  linear  motion  and minimizes the effect of loading force during the printing process.

        Secondly, check the parts for wear. All parts have  life and some  parts will wear  over time.  Therefore, make sure that the screws/

ball screws and bearings are regularly maintained,  lubricated and in good condition. If there is wear, parts need to be replaced. If you 

hear any rolling or rubbing sound, be sure to recheck the leveling process of the components and forming platform.

       Again, check for loose parts. Check the nut on the z-axis lead screw. If there is excessive clearance (looseness), it may also lead to 

unstable z-axis ripple during printing.  Usually the nut has a second loaded spring nut,  which can cause problems if  it is not properly 

installed (or worn).

         In addition, z-axis instability may also occur due to screw bending or off center. At this  point,  the screw  must be replaced.