- keeping the cool end on the extruder barrel cool
- cooling the printed part as it prints
So, when and why would you need to cool these?
- Fan for Barrel Cooling
Some materials, PLA in particular, exhibit "melt creep". This phenomenon results in molten material working its way up from the hot end (nozzle) into the barrel and, in some cases, even all the way up to the filament entry point into the extruder. This is not good! The goal is to have a small melt zone with solid (i.e. unmelted) filament behind it to effectively push the filament through the nozzle. Once molten filament makes its way up to the cold zone (the PEEK section on typical extruders) it can harden or compress and jam your extruder. As mentioned above, PLA is nearly impossible to print without an effective cool zone to prevent this creep from occurring.
Most people have not really thought about the dynamics of heating/cooling the nozzle/hotend. Very little airflow pointed directly at the PEEK (25mm fan) is all that is required to lower the temperature by at least 20°C. Too much air, or air directed at the hot end/nozzle is only going to create problems for the PID to keep the hot end at the set point and use more power than necessary. You can use Kapton tape or aluminum foil shield to isolate the hot end if needed. Please consider using the right size fan for the job, bigger is not necessarily better and can make the situation worse.
NOTE: The way the Rostock delta head is designed, the spacers are exactly 1" tall so a 25mm fan slides right in. The lower part of the platform where the delta arms are attached makes a great "wind brake" to keep the fan on the PEEK and not the nozzle.
And as Polygonhell states "don't forget to retune your PID settings after you add a fan (with the fan on of course)."
It is perfectly fine to run the fan at all times. You will find that the PEEK barrel will stay nice and cool and you won't have problems with other materials. Higher melting temp materials like Taulman nylons (there are 2 types now) require higher melt temps - right at the lower limit for melting the PEEK - so the fan provides a degree of safety for these materials. I have my fan wired to a simple on/off switch and leave it on all the time when printing. I've had absolutely no clogs or issues printing PLA.
- Fan for Part Cooling
NOTE - this has been superseded by tip 12 here: viewtopic.php?f=36&t=7361
Certain materials like PLA remain plastic for a long time. Part geometry and infill also have an effect on the duration of this plastic state. There is a fine tradeoff between cooling a part so that it does not warp or distort and keeping it warm enough so the next layer can effectively bond to the previous layer. Excessive cooling can also CAUSE parts to warp and delaminate due to built up shrinkage stress in the printed part. ABS is particularly notorious for this since it has considerable shrinkage upon cooling.
But don't despair! It is actually quite simple to learn how to deal with this printing challenge. It does take a little experimentation and experience but once you understand it, you can reliably determine how much and "if" you need to cool your print. Let's take a look at some scenarios.
PLA can almost always benefit from some cooling air flow to help solidify the part as layers are built up. PLA stays soft for quite some time and is prone to warping and distorting due simply to plastic flow. A fan - or fans - aimed at the part can prevent this. I prefer to position the fans on the build platform rather than the printing head. This gives me more direct cooling to all parts of the print and removes mass from the print head. It also allows me to use several smaller fans distributed around the part rather than one big fan blowing a lot of unused air. I actually use three 40mm fans space 120° around the part. Adjusting the fan speed gives me control over cooling.
One tip, don't use the print fan on the first few layers. You want those to stick to your build surface and cooling them as they form is a recipe for pealing trouble.
Very Small Parts
Small prints (with a foot print around 15mm x 15mm or so) in all materials can benefit from cooling as they print. These small parts usually don't have a chance to effectively cool before the next layer is applied. You can also slow down your feedrate to allow cooling.
Prints with Thin Cross Sections
Prints in all materials that have thin cross sections or thin columns can benefit from cooling as they print. These thin cross sections usually don't have a chance to effectively cool before the next layer is applied.
Prints with Solid Infills
Prints with or near 100% infill can also retain heat and stay soft for long periods of time. Fans are an effective way to cool these parts.
NOTE: Most Arduino based controllers like RAMBo have fan ports. The RAMBo port is great for the part cooling fan (or fans). That way you can control it from gcode. For instance, with PLA I put down the first 4 layers without the fan and then turn the fan on 50% for the remainder for most parts or 100% for thin/pillar types of parts.
I'm sure I missed a few considerations so feel free to comment.