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.
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:
- Mounting the lead screws and linear rails in the 3D printer frame, but not tightening them down yet.
- Fully assembling the Z carriage outside of the 3D printer.
- Installing the Z carriage by connecting it to the linear rail carriages, and threading the lead screws through the lead nuts on the carriage.
- 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:
- Placing and securing the linear rails and lead screws parallel to the aluminum extrusion of the frame.
- 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.
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:
- Make sure that the frame is square and true.
- Install and secure the linear rails and lead screws.
- 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.
- 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.
Further progress on the 3D printer
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.
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.
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.