hotend postmortem

August 17, 2011

Following the last post I’ve sliced open the old ptfe thermal barrier in order to get an idea as to why it leaked/jammed. In the first image, below, it can be seen that the pla made quite a bit of room for itself increasing the ptfe inner diameter! If you look closely in the lower section close to the transition from threaded to smooth section there is a little blob of orange pla.

I have a cheap’n’cheerful usb microscope which is useful for this type of situation…

Above is a slightly closer view of the orange blob.

Above is a closer image of the pla blob. Sorry about the lack of a scale, if it helps the threaded section in zoomed-out images is M6.

Above is a microscope image of the od, in particular the threaded section. The dark region just above the (admittedly dark!) threads is possibly of interest….

Above is a closer view of the dark region in question. There does appear to be some orange pla exiting this hole. It is in the same position as the blob on the id… so this is likely the leak.  I suspect you then get into a vicious cycle of jamming-leaking-jamming which eventually leads to a plug which is too much for the extruder to overcome.

On a brighter note here are some images of the makergear hotend:

The hotend has whats called a groovemount, this is visible in the first image. This slides onto a plywood plate which can be purchased from makergear. In my case, having a laser and some ply lying around, I cut one out myself (sorry for the lack of photo!). Its basically a rectangular piece with a U-shaped slot/cutout for the groovemount to slide onto. The plate’s thickness was about 0.5 mm too much so I shaved that off with a sharp chisel. The plate mounted on the Prusa x-carriage without fuss, over the existing ply plate. This raises the extruder a shade but the hotend is shorter than the old one so no z-axis height is lost.