If you choose to print tiny objects, consider printing many of them together. By printing multiple smaller parts together the 3D printer can ensure it has a suitable minimum layer time because it spends a longer amount of time printing multiple parts, so each layer takes longer. This may sound like all you are doing is making your 3D print take a longer time to complete, and that's true, but you are also allowing each layer on each part to cool enough to accept more molten plastic on top. If you print just one small part, the slicer will slow down nozzle movements so the layer time is slower, but because the hot-end nozzle head is never too far away from the single part being printed you may still not have enough time to cool the layer.
It's often better to end up with two or three small parts printed together, and they may take only slightly longer to print that one single part due to the minimum layer time condition. This technique has one down side: You may not want copies of a part, and you may start seeing tiny defects on the outside surface of an object where the head moves between the parts. These visual flaws may not be problems for functional parts, but for a model intended for display, you probably require the best possible appearance.To address the speed problem, you could slow the entire print speed, but there's a better option: Define a minimum print time per layer in Slic3r. In Expert mode, choose Filament Settings and Cooling → Enable Auto Cooling. You'll probably find that this setting is a good one to keep enabled all the time. Read on to find out why.
When you define a minimum layer time, Slic3r knows that it has to automatically calculate and slow any layer to this set speed. The result is that tiny objects automatically print slowly, and bigger parts automatically take longer than the minimum layer time and so are not slowed. Thus, the Auto Cooling setting gives you the best overall print speed and quality.
Automatic cooling is really important with some objects, such as pyramids. A pyramid starts with big layers at the base and print faster as the layers get smaller toward the top. If you don't set a minimum layer time, the pyramid still looks great until the print reaches the top, where it's ruined by the very fast printing of tiny layers — which usually results in a blob of plastic instead of a defined, sharp peak. When you set a layer time of around 15 seconds, the print automatically slows as it gets closer to the top, and the model prints well.
You print objects quickly without using the slowing-down method just described, but it takes some time to discern when this technique is appropriate. One way to achieve this result is to use a directional fan to force-cool the layers immediately after they print, but we recommend using this trick only for materials such PLA and for nonheated print beds. You can use 3M painters tape to hold down PLA printed parts when not using a heated bed.