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Z Axis Problems

If you've reached this page, then your probably a bit pissed off. All that time and effort and the damn thing just isn't moving up and down reliably.

But stop for a second and appreciate how you've just managed to make a 3D mechanical structure without using any precision components or tooling. We have completely bypassed traditional engineering, broken lots of rules and still come up with something which does actually work (honest). The design is, however, unforgiving, so if there's any mistakes in your configuration your z axis will not work. This page will help you fix that.

  1. Check you followed the assembly steps correctly.
  2. Check you followed the assembly steps correctly.
  3. Check you followed the assembly steps correctly.

Seriously, this guarantees alignment and precision. Once you're happy that you've assembled correctly the bottom line is that the torque required to spin each z post is too high.

The first thing to check is the free running resistance of each z post. Derail the belt and manually spin each post to check for smooth, even rotation. You should be able to do this with only your thumb and first two fingers on the threaded section. There should be no high spots (lumpy rotation). If you have problems rotating inspect the post for problem areas:

  • When unconstrained by the lowest two set of locknuts, the post should float up and down in the bottom corner bracket easily when the bed is wiggled at that corner. If not, a quick bodge is to rub the post up and down against the tight spot in the corner bracket hole. (This works well, and filings should be inconsequential as the lateral loading will be taken by tension bracket).
  • Check your locked nuts aren't to tight on any of the running elements.
  • Ensure the posts are fully lubed along the length which the bed corners run.
  • Check the base diagonals are not touching the bottom of the z posts.

The biggest source of problems is the belt tension. Z post rotation friction increases with belt tension. Start testing with completely slack tie brackets.

  • Start with a slack belt, on the verge of slipping over the pulleys. Try it. If the belt slips over the pulleys and does not bind wind the tension up a bit with the tensioner.
  • Ensure that your belt is running correctly over the pulleys: it should not catch the rims - if this happens it will spike the tension and cause motor skips.

-- Main.EdSells - 11 Apr 2008