Hi all. Thought I would share a couple of thoughts I have on the subject of heat creep and jams. For the purpose of the diagram i’ve created, i’m intending only to communicate generalized associations between ‘Print speed’, Hotend Temperature and filament jams’. I’m also not trying to address any of the clogging situations having anything to do with foreign debris in the nozzle tip. IE, I’m only describing jams typically associated with heat creep, where the filament becomes difficult to pull out of the head even at temperature.
In the diagram below, I’ve tried to describe the correlation between hotend temperature, print speed and risk of filament jamming. And to be clear, when I say speed, i’m simply describing how much filament moves through the heatsink at a rate. The specific numbers (mm/s) are somewhat irrelevant. The fact is this correlation exists for every type of hotend/speed combination.
There’s also another factor that is even more challenging to isolate which is filament glass transition and melting point (2 different temperatures). Technically speaking, these temperatures are not the same across all filament materials. IE, Red PLA from one manufacturer will almost certainly have a different melting point from another manufacturer. This means that the jam risk factor can simply be higher based on choosing a different filament.
Generally speaking, the higher the heat travels above the heater block, the higher the risk of filament jams. While I love the ease of printing with PLA, it has proven to be a little more challenging when trying to print higher quality (slower speed) prints. These are the times that i’ve most often experienced filament jams of this type.
Also, don’t overlook retraction settings. This can be a less than obvious factor as well. The higher the retraction distance and the frequency of how often retraction occurs, can significantly contribute to this prob. Recall, retraction is pulling the already filament back up toward the heat sink. The higher the filament that has hit the glass transition temperature, the greater the chance of it jamming in the heatsink. Example: the combination of a slower print speed and high retraction distance can lead to a jam. It’s entirely possible that without changing any retraction settings, a simple increase in speed can eliminate the risk. Conversely, reducing the retraction distance from .8mm to .4 or .2mm may also eliminate the jams. As you can see, there are a variety of ‘levers’ you can pull in order to change the risk factor of jamming.
One last factor is airflow across the heatsink. In most cases, this may be difficult to alter as the fans on heatsinks are generally fixed speeds and yield a static cooling effect at all times. This is at least in part, why you find quite a few heat sink fan shroud designs.
Sorry to be long-winded. I hope this helps some of you. Here’s Lulzbot’s extensive reference to 3d Print filament if any of you are interested in reading. https://devel.lulzbot.com/filament/.
