Octagon tower test print

This model grew out of the need for a small, quick test print to help verify bed adhesion after changing to a new filament type, (especially one I haven't used before) cleaning the bed, adjusting z offset etc, which I later added two small towers and bridges to for doing a basic test of bridging and stringing artefacts.

It uses only 4g of filament and takes only 5-20 minutes depending on print speed and can help check and fine tune multiple print settings quickly.

It should be printed directly on the bed with no build plate adhesion settings ("build plate adhesion type none" in Cura) and I always print it with a 0.2mm layer height for speed.

The other print settings such as hotend/bed temperatures, retraction settings, print speed etc should all be set to the values that you propose to use with the same filament with the print job you are going to do after this calibration print.

Multiple aspects of the printer setup for the filament can be evaluated quickly with this test print:

1. Bed adhesion. Watch the first layer as it goes down, it should be smooth and flat. If there are gaps where it pulls together into clumps you have under extrusion, this can happen with TPU for example. If it “bubbles up” in places you have problems with bed adhesion, which could be many things - dirty bed that needs cleaning, z-offset not set properly or bed levelling required, hot end temperature too low, print speed too high for the material etc.
   
   The underneath of the final print should have a smooth uniform finish like the example photo. If the bed is already clean and the z-offset is correct try increasing the hot end temperature in 5C steps. I'm finding with the brand of plain PLA I use I need about 205C, but some multiple colour filaments need about 215C for example and will bubble up at 205C. Every filament has a different optimal temperature.
    
2. Layer bonding. If you bend the base of the finished print it should be flexible but quite strong - at least in PLA and it should not “crackle” when bending. PLA should be quite tough and not break until it is bent a lot, nearly 90 degrees. (Wear glasses when testing this and bend it away from you as it can shatter suddenly) If there is poor layer bonding the base will “crackle” as you bend it, long before it breaks, this is the layers moving across each other internally.
   
   I find this happens easily with PETG printed at too low a temperature, it will both crackle as you bend the base and then shatter easily. Increasing the hotend temperature should help and in the case of PETG reducing the part cooling fan.
   
   The second layer bonding test you can do is to try to bend the tower to the side - with well printed PLA it should bend about 20 degrees to one side without breaking and be stronger than it looks, however if you print something that is brittle it will snap very easily with almost no force, this shows poor layer bonding. I've found huge differences in layer bonding strength with different types of filament, for example the silk PLA I've tried is very weak compared to normal PLA and fails the layer bonding test, and I haven't had a lot of luck with PETG either even at higher print temperatures.
    
3. Stringing / retraction - this is not a fancy temperature tower but is a good quick check that the hot end temperature and retraction settings you are going to use aren't going to generate a lot of stringing. With the settings I typically use I get NO stringing on this test print at all in PLA, however I have not been able to eliminate it completely with PETG.
   
   In general higher hotend temperatures will increase strength and layer bonding but increase stringing while lower temperatures will reduce or eliminate stringing but can cause a weak/brittle part which is why it's helpful to have both a stringing test and brittleness test in the same part.
    
4. Bridging - There are two small bridges which will help you adjust your fan speed for optimal bridging. Unless you're using PLA you'll want the part fan speed to be as low as possible while still giving good bridging results. This is especially the case with TPU where a high part fan speed may blow hard enough to deflect the material as it cools.

Because this test print only takes about 10 minutes I will typically use it before I start any big print that is going to take a long time, or anything that is going to be a bit challenging from the perspective of bed adhesion or stringing, especially if I'm using a filament I haven't had much experience with, and I will always do this test print first if I have recalibrated the bed or done maintenance on the printer that might have affected the calibration.