A couple of months ago, we discovered the wonder of fans. We thought we found a great leap forward in terms of print quality when we began incorporating cooling fans nearby the print head. The focus was cooling the plastic quickly after it’s having been extruded, and the result was much smoother prints, particularly with small parts or delicate areas. Towers are a good example of the issue – with a relatively small cross area, and continual build up of material in the same small area, the plastic stays too warm, practically molten, and eventually slumps. Rather than a tall spire, one ends up with a lumpy mess. Fans come to the rescue here by cooling the plastic more quickly, thereby allowing it to solidify, with the final result looking more like what one intended.
In our latest design, we’ve been trying to hammer out the details of our fan configuration, and along the way, decided to ditch fans altogether. Initially, we assumed we would be using two fans, pointed towards each other, and just below the print head. We purchased 3 different sized of fans to experiment with – 20mm by 20mm, 40mm by 40mm, and 60mm by 60mm. Each pair had a different location within the printer – the 20mm fans were about an inch away from the print head, the 40mm fans were about 2.5 inches away, and the largest fans were about 11 inches away.
Here is a picture of the 40mm fans attached to the print head:
These were the fans we used:
Although we used a variety of test objects, we settled on a tall (70mm) three sided pyramid as our primary test object. The objective was to print a tall, tapering object and see where it began to slump – in other words, at what point was the plastic being extruded too quickly, such that it could not cool enough to maintain its structural integrity. Our assumption was that the fans would promote more rapid cooling, and thus the object would more structurally sound.
To our surprise, the increase in airflow gave us only marginal gains in the structural integrity of the test objects. We additionally attempted to increase the airflow by supplying the 40mm fans with more voltage. While this improved things, the results were not what we were looking for. As can be seen in the picture below, the four different fan configurations we tried gave only small improvements in the final print’s quality.
Unsatisfied by the results we were getting, we began looking for other options. Skeinforge has a plugin called “Cool”, which turned out to be just what we needed. Particularly, one of the settings in the Cool plugin allows you to define a ‘Minimum Layer Time’. What this does is let you specify the minimum amount of time it takes to build each layer. Another setting, “Cool Type”, tells Skeinforge how to deal with layers when they would otherwise take less than the specified minimum time – we use the ‘Slow Down’ option. Essentially, how this works is you specify a minimum time (in our case, 10 seconds seemed to work well), and then for any layer small enough, the print head moved correspondingly slower.
Here is a resulting print. Note that both parts below were printed without the use of fans, the only difference being the use of the Cool plugin.
Our conclusion is that, while fans are of limited usefulness, Skeinforge’s Cool plugin is particularly useful for small parts that are prone to becoming too hot. I might add that the Cool plugin is much more easy to implement too.
