3D Printer Calibration by Printing Many Cubes
I’ve spent a while printing calibration cubes. They’re not the most exciting prints, but they help a lot with solving calibration issues with the printer. A calibration cube is a 20x20mm cube with X, Y, and Z on its corresponding axes. You can find this model on printables.com
This cube usually prints fast and shows clearly surface issues, dimensional issues, and other artifacts. It’s rather handy that the letters of the axes are on the cube so you can know the orientation of the print and where the issue may lie.
Rather than just using the standard 20x20 calibration cube, I’ve chosen to scale the cube up to 40x40mm as it allows me to see more exaggerated issues, and I generally find them easier to resolve when exaggerated.
Troubleshooting Process
Firstly I print the calibration cube. Then note down all the issues that I find with that print and attempt to deal with them one by one. The issues that I found with my first calibration cube were the following:
- Ghosting on the X
- Ghosting on the Y
- Gaps in the base of the print
- Seemed slightly off-square
It’s important to tackle a single problem at a time, as it’s very easy to get carried away and then not know what fixed what, or what change could have introduced another issue.
Squaring the Prusa Mini
Firstly I’m going to square up the printer, this can be done without any special tools, and the printer can be used to square itself. I’m not going to go over the process as Prusa has a great knowledge base article on the subject. Just follow that article and you’ll be golden. I found that my X-axis was slightly out, not by much, but rather have it perfect than not.
If including this step in the troubleshooting, it’s important to carry out this step first, as it will undo any of the next steps**. All calibrations require this step to be finalized.
I then printed another calibration cube to assess the changes and compare it to the previous cube at the start of this process. This cube had all the same issues apart from the dimensional accuracy was now corrected even though it was 0.03mm out previously.
Belt Tension
I’m going to address the belt tension on the X and Y. This is usually down to two things, either the belt tension is incorrect or there is something else loose on the printer causing vibrations. Usually, it’s the belts, as through use these can become loose, however, the belts being too tight can also cause ghosting as it’s creating feedback that isn’t expected and compensated for.
There are two ways to tighten the belts, however I feel that rather than picking a single method they should be used in unison to make the job easier.
The first method is with the GT2 belt tension meter which can be printed. It requires Prusament PTEG, as that’s what the tool has been calibrated against, any other material will skew the results and reduce the reliability. The tool is rather simple to use with the guide on the Printables Site. However, that being said I still think the second tool for belt tension should be used once the GT2 meter has been centered.
The second tool is the belt frequency tool. The instructions indicate the position of the X and Y, then give feedback on the sound of the belt when strummed. This allows you to dial in the correct tension, however it’s difficult to use for larger changes. Hence the need for the first method to get in the right area.
Once I completed these steps to tension the belts I then you guessed it, printed another calibration cube. This cube printed correctly, with no ghosting on the X or Y, along with it still being square.
It’s important to test for issues that you may have already fixed in previous steps, as with all print changes they could have effects on other parts of the print. It’s not uncommon for belt tension changes to pull the printer out of being square.
Cleaning the Extruder
During the printing of the last calibration cube, I heard some clicking coming from the extruder. This is either two issues, the extruder has some rubbish in it, or the nozzle is too close to the print bed. The later certainly wasn’t the case, as I knew it was too far, as there were gaps in the base of the print. So it had to be cleaned, once again I’m not going to cover the process here, there is surprise surprise another great knowledge base article on how to do this. Can you see why now, I went with a Prusa?
Again I printed a calibration cube after cleaning out the extruder, and yes it needed a clean. This time, there were no clicks and everything printed great with the only issue being the base of the print with some slight gaps in the first layer.
Z-Offset
To solve the base of the print, there are some gaps, which usually means that the z-offset is a little too high. There is a built-in test for this on the printer, which allows you to edit the z-offset live. So I carried that out a couple of times till I got it where I kinda wanted it.
This time I didn’t print a Cube, as I only want to check the bottom of the print and want faster feedback while I dial that in. This is where the 40mm slab comes in. It’s a 40x40 slab, that is 2.4mm high. The reason for this height is that I usually print with top and bottom shells set to 1.2mm so it lets me check both at once, and this prints much faster**.
After a few runs with this model, watching it print while playing around with the z-offset I managed to get the perfect first layer, this is on the smooth plate, so this would have to be done again on the other sheet types, that by the by.
Now that sorted, guess what? Yep, I printed another calibration cube, and this one was completed with zero issues, and all issues that were in the first cube at the start of this process were no more.
The printer is now calibrated and ready to push some plastic! All with a piece of mind.
Next Steps
So the next step is to reset the clock, I usually perform this every 500 print hours, or when issues arise. There is another reason I carried out this work, apart from the print issues I was getting, which is the next project.
The next project is making the printer as quiet as possible. The issue is that the printer is in the same room where I work all day, and it’s rather annoying having the noise of the printer going while in meetings. There is the long-term goal of building an enclosure, which will certainly help with the noise levels. If I can get the levels down as much as possible before the enclosure, then it’s an even greater win.