I have probably used my Longmill MK1 about 14 hours since I installed the “self adjusting” anti-backlash nuts. Movement can be detected when small forces are applied to the X, Y, and Z axis when the machine is stopped. After investigation, it is the newest design “self adjusting” anti-backlash nuts which is resulting in noticeable backlash.
Since the new design can not be adjusted there is no remedy with the “self-adjusting” designed nuts to control lash once they wear a bit.
When looking at the new design, I am a bit perplexed. The “backlash” is an axial “linear” error, but the new style tries to solve this with a spring loaded radial force on the lead-screw. It was decided to return my machine to the original design, but with a modification to improve the old-style anti-backlash delrin nuts.
The first step was to drill out the existing threaded hole to the clearance size needed for a 10-24 screw ( or whatever screw size you desire) Then the hole was drilled further (toward the mounting nuts) and tapped. The spring from the “self adjusting” nuts was installed on the screw to press against the cantilevered “tongue” on the anti-backlash nut. The screw was adjusted to remove lash without excessive drag on the lead screw.
The Z axis is particularly prone to error due to tolerance stack ups ( slops) between the workpiece and the spindle. This may not be apparent on contour cuts, but may be objectionable on “advanced V carve” designs. The first Z error is any “slop” in the V rollers on the y axis. The next error is the V roller slop on the Z axis assembly. Then there is the error from the anti-backlash nut for the Z axis leadscrew. There may be some minor contributions if the spindle has axial slop ,if the Z axis lead-screw has some slop in the upper bearing assembly, the cogged belt is loose, or the X axis beam has some flexure. I will disregard these in this discussion.
Depending on the cutter’s sharpness, resistance of the material , plunge speeds and feeds, the Z axis plunge depth can have depth variances/tapers on the work piece due to the accumulated “slops” in the aforementioned areas. The original plunge may be a bit shallow and then taper to the proper depth as the weight of the spindle assembly and gantry gradually return to equilibrium. This may require a “skim pass” or very slow feeds and plunge speeds to create desirable results (all increase the processing time). It is desirable to eliminate as much “slop” and possible
This is an image of the modified “old style” anti-backlash nut.
