Wavy Z-Axis

Hello All,

I just finished assembling my first printer, so far everything has worked out well - except for one small issue. I have some sort of oscillating wave as the printer climbs higher up the Z-axis. I bought the HICTOP kit from Amazon and I've read a little bit about the Marlin firmware for Z-axis troubles but I'm not sure that's the issue? I've got lead screws instead of the threaded rod.

I've attached a picture of the test file HICTOP includes as well as another small bracket I made, both have the 'wavy' z-axis. Any ideas?

If you measure the distance between waves, is it about 8mm? If so that matches the lead on a TR8 lead screw and the problem is most likely that the coupler between the motor and the screw is not completely concentric, so the screw gets pushed off-centre as it rotates. Another possibility is a bent lead screw, but that's less common (more likely when using threaded rods).

Getting the lead screws concentric with the motor is remarkably difficult, to the point where I would put this on the design flaw list of the common printer designs (I'm guessing the printer you're talking about is a Prusa i3 like this one?)

Flexible couplers like the ones in the link make sense if the lead screw is properly constrained in a bearing block, but since the I3 doesn't have that they are counter productive. It's next to impossible to get flex couplers to be well aligned. I replaced mine with solid couplers and machined the ends of the lead screws to match the diameter of the motor shaft. It's still very difficult to get them well aligned, so I have a rebuild of the Z axis on the todo list.

One option that can work well is various designs of linkage that allow the nut on the lead screw freedom to move in the XY plane. It's a bit hacky, but it can give good results.

James,

Yes - the distance was almost exactly 8mm (7.6ish). The link you sourced is the exact item I bought - I figured it might be a good (not too expensive) first printer to learn the ropes on.

Well you hit the nail on the head with the lead screw and the coupler. I found that the left lead screw got hung up on one of the small set screws in the coupler and did not fully seat to the bottom against the motor drive shaft. I fixed that and also added some small washers between the extruder mount and the extruder motor as the M3 screw seemed to be a hair too long and allowed for a little play.

My vertical walls are now straight! Thanks a lot for your help, I really appreciate it.

My first 3D printed item is now in use in my apartment (a bracket for a door open/close sensor). It feels pretty cool to be able to design and make actually useful things!

Now it's time to start upgrading this thing - any items I should be looking at?

Glad you got it working. Yes, it's an amazing feeling to be able to design and build things that interest you. Probably the single biggest upgrade is to build an enclosure for the printer which will make it easier to print with abs. You can sidestep the problem by using nylon and petg instead, but abs is cheap and other than the warping/splitting (that the enclosure avoids) is pretty easy and nice to print with.