filament piles up in extruder cavity

Whenever I start a long print, after a while (15 or 20 minutes or so) the filament is jammed in a cavity on the bottom of the extruder to the hot end. for shorter prints that only take 5 or 10 minutes I do not have this issue.
In the pictures, you can see the extruder as it is mounted and when I open it up after the print, it looks like in the second picture. Of course, when that happens, there's no filamaent anymore coming out of the printer so the object is lost.



Does anybody know why this happens? Is this beceause the extruder is "too fast", or, is it because the whole extruder on the x-carriage is getting that hot that the filament is already to flexible in teh cavity? What is the cavity for anyway... does it have a purpose?

Anyone who experienced the same and found a solution?

Kind regards and thx for any feedback,

Wim

To me, it looks like the excess heat that builds up is causing the filament to become flexable, just as you say. Is there a way you can make the gap in that cavity shorter, so there is less distance from where the filiment is being fed into your extruder?

You might need a longer barrel to stop the heat migrating to the top so quickly as it's obviously too warm just under the extruder. A fan might help to keep the upper end of the hotend a bit cooler, but looking at yours, it looks like theres not much length to cool as it seems quiet short.

print one of these
[terawatt-industries.github.io]

bore out the the hole in the budapter a bit just to make sure it allows your filament to go through freely and with little to no friction, then place it in the cavity.

There should be no cavity above your hot end. The top of the hot end - at least the top of my j-head hot ends - is meant to be inserted INTO the extruder body. If you have a hot end design that does not project like this, you should have not have a cavity in the bottom of the extruder so that he two can meet flush.