After building the frame, I have made some further progress with the new 3D printer. I installed the Z carriage of the printer and mounted and aligned all other components that facilitate the motion on the Z-axis, such as the linear rails and lead screws.

As expected, aligning the linear rails and lead screws was a lot of work. It took me multiple attempts to figure out how to properly align these components.

Installing the Z-axis components the wrong way can cause the Z carriage to move with a lot of grinding and squeaking, or even to get stuck and not move altogether.

In this article I will show how I installed the Z-axis parts, share the methods that worked and did not work, and share the rest of the progress on the new 3D printer.

Top front view of a 3D printer Z carriage made out of 2020 extruded aluminium inside of a custom 3D printer.
Some of the progress on the Z-axis motion components.

How (not) to install Z-axis components in a 3D printer

The first method

In my first attempt at installing the Z-axis components I tried the following approach:

  1. Mounting the lead screws and linear rails in the 3D printer frame, but not tightening them down yet.
  2. Fully assembling the Z carriage outside of the 3D printer.
  3. Installing the Z carriage by connecting it to the linear rail carriages, and threading the lead screws through the lead nuts on the carriage.
  4. Adjusting the positions and angles of the lead screws and linear rails to get them parallel.

This did not work at all. I ended up with a Z carriage that had a lot of problems moving due to misalignment and binding.

It was impossible to get the alignment of lead screws and linear rails right. With two linear rails and three lead screws there was always something that couldn’t be mounted perfectly parallel, because the Z carriage constrained it and prevented it from being mounted in the ideal place.

There were times when I thought that I had everything parallel, only to find out that when I moved the Z carriage all the way up or down, something was still binding.

The second (successful) method

After this unsuccessful approach, I realized I had to make sure that the linear rails and lead screws were parallel first, so I tried a different method:

  1. Placing and securing the linear rails and lead screws parallel to the aluminum extrusion of the frame.
  2. Assembling the Z carriage piece by piece in-place in the 3D printer.

This method worked perfectly and got the Z carriage to the point where it could travel its full range without binding.

Because the frame is used as a reference point to get things parallel, it is absolutely crucial that it is perfectly square and true. If you start out with the aluminum extrusion of the frame misaligned, you will have very small chances of success.

The difference between the methods

The main difference between the two methods is as follows:

In the first method, when securing the linear rails and lead screws, their position is constrained by the lead nuts on the carriage. If the carriage (and lead nuts) is slightly off from the optimal location, it might not be possible to get the lead screw mounts in the right place. A millimeter offset, or even less, can be the difference between misalignment & binding, and smooth travel all along the Z-axis.

In the second method, the exact dimensions of the carriage (and thus the position of the lead nuts) simply adapt to the position of the linear rails and lead screws. Because the linear rails and lead screws are already parallel, the carriage is guaranteed to be able to travel smoothly up and down.

Further down the page I added some step-by-step pictures to further illustrate this.

Summary

The main idea that I want to communicate is that when you build the Z-axis of your 3D printer, the order of operations is crucial. Aligning the linear rails & lead screws first and then assembling the carriage produces a better result than vice versa. In summary:

  1. Make sure that the frame is square and true.
  2. Install and secure the linear rails and lead screws.
  3. Assemble the components of the Z carriage in-place in the 3D printer.

Building a printer frame out of mostly lasercut parts would be a lot easier. With lasercut parts things are exactly where they should be, and there are less possible alignment issues to worry about.

When building a 3D printer frame out of mostly aluminum extrusion however, I think this is the way to go in terms of Z-axis assembly.

A rough guide to aligning the Z-axis linear rails, lead screws and installing the Z carriage

I have added pictures of aligning the linear rails & lead screws and assembling the Z carriage below.

Some of the steps might be a bit specific to the custom 3D printer I am building, but I hope that you can still find some use in it. I think the general approach can still be applied to other 3D printers.

After finishing the prototyping stage I will rebuild the printer with 3D printed parts out of a more temperature-resistant plastic. When I do this I will also use this guide to make sure I do things in the right order.

Keep in mind that this is by no means a complete guide, as several minor steps are missing.

A hand using an allen key to tighten mounting bolts on a MGN12 linear rail mounted to 3030 aluminium extrusion.
Install the linear guide rails by bolting them to the aluminum extrusion. I used a 3D printed jig to align the linear rails while installing them, so that they end up perfectly centered and parallel to the aluminum extrusion.
A partially assembled Z carriage and a partially assembled triple-lead screw belt assembly inside of a custom 3D printer.
Install one side of the Z carriage as well as the corresponding lead screw + lead screw mount. Don’t tighten the lead screw mount to the frame yet. The lead screw should still have some movability on the XY plane.
A close-up of 3D printed components that make up part of a triple-leadscrew assembly inside of a custom 3D printer.
Before tightening the lead screw mount (bottom), the lead screw has to be positioned parallel to the frame extrusion. To achieve this I did the following:
  • Lower the lead screw bearing mount on top of the carriage.
  • Raise the lead screw bearing mount to right above the top end of the lead screw.
  • Adjust the position of the lead screw mount at the bottom, so that the top end of the lead screw lines up exactly with the bearing in the bearing mount.

The goal here is to find the lead screw mount position where the entire length of lead screw matches the (XY) position of the hole in the lead screw bearing. This is the position where the lead screw is parallel to the vertical frame extrusion.
After I found that position, I secured the lead screw mount and the lead screw bearing mount to the frame.

A partially assembled 3D printer made from 3D printed parts, 3030 and 2020 extrusion.
Repeat the previous steps for the other side of the Z carriage.
A partially assembled aluminium Z carriage in a custom 3D printer.
Insert the aluminum extrusion at the rear of the carriage and the corresponding lead screw components.
A hand holding a digital angle finder (indicating 90 degrees) next to the aluminium Z carriage of a custom 3D printer.
Make sure that the Z carriage aluminum extrusions are positioned perpendicular to each other.
A hand using an allen key to tighten bolts on the Z carriage of a 3D printer.
Bolt the Z carriage extrusions together.
A hand holding a digital angle finder (indicating 90 degrees) up to one of the lead screws in a triple-lead screw system.
Move the rear lead screw mount along the X-axis until the rear lead screw is perpendicular to the Z carriage. This step requires the Z carriage XY plane to be parallel with the 3D printer XY plane.
A hand using an Allen key to tighten the bolts on a custom 3D printed component in a 3D printer.
Bolt the rear lead screw mount in place.
A hand holding a hex key and tightening a bolt on a 3D printer Z carriage.
Secure the bolts that clamp the Z carriage to the linear rail carriage blocks.
The inside of a custom 3D printer, containing 3D printed parts, lead screws, a stepper motor and a loose belt.
Lift the Z carriage & lead screws above the lead screw mounts and slide something flat under one of the lead screws to keep everything in place.
The inside of a custom 3D printer, containing various components including pulleys and two tightened GT2 timing belts.
Slightly lower the carriage & lead screws and install the upper pulleys and belts of the motion system. Don’t tighten the pulley grub screws yet.
A partially assembled belt system of a triple lead screw Z-axis motion system inside a custom built 3D printer.
Install the lower pulleys and timing belt and lower the carriage & lead screws back down.
A fully assembled and tightened belt system that is part of a triple lead screw system inside a custom built 3D printer.
Fully tension the lower timing belt by sliding the idler pulley arms along the extrusion and securing them in place. Tension the stepper motor timing belt by doing the same with the stepper motor mount. If necessary, adjust the individual lead screws so that the Z carriage is leveled. After this all pulley grub screws can be tightened.
Top front view of a 3D printer Z carriage made out of 2020 extruded aluminium inside of a custom 3D printer.
Install the remaining aluminum extrusion (the extrusion that is used to mount the heated bed on) into the Z carriage.
A hand using a hex key to tighten the bolts on a grey 3D printed component that is mounted to aluminium extrusion.
Raise the carriage all the way up and secure the rear lead screw bearing mount.

Further progress on the 3D printer

Motion test

Now that all the Z-axis components have been aligned, the Z carriage travels very smoothly. Especially with the 1/256 micro-step TMC2660 drivers on the Duet Wifi.

There is a slight rattling audible in the video, due to one of the lead screws moving around in one of the top-mounted 608 bearings. The bearings I use for prototyping are cheap and have loose tolerances. The 608 bearings in the final build will have narrow enough tolerances to not have the lead screws ratting around in them.

Belt tensioning arms

I have had to reinforce the two belt tensioning arms that tighten the long Z-axis belt. There was a lot more tension on the belt than I anticipated. The belt tension pulled the arms upwards out of alignment.

Thickening the arms and adding extra mounting points solved the problem.

Two 3D printer belt tensioning arms. The left uses idler pulleys with built-in bearings, the right uses regular GT2 pulleys.
One of the old belt tensioning arms (left) next to one of the new ones (right).

I also moved away from using idler pulleys with built-in bearings. Instead I switched to ‘regular’ GT2 timing pulleys and flanged bearings. The idler pulleys w/ bearings had too much run-out, resulting in a wobbly timing belt.

Other thoughts

The lead screws still need to be lubricated, and during the final rebuild I might switch to anti-backlash nuts, but I am already very satisfied with how the Z-axis runs. Of course, I will have to see if the visually smooth travel also results in high-quality prints, or if any printing artifacts show up.

What is next?

The next step in building the 3D printer is to install the CoreXY components. The X- and Y-axis linear rails and carriages, stepper motors, idler pulleys, and so on.

If you find this article useful, please share it or leave a comment. I love to hear your feedback and questions!

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