Early experience with Thingfarm J-head hot end

[Graham Klyne]

FYI, my extended barrel J-head hot end arrived on Saturday. The new extruder
has been doing sterling service over the weekend ... I nearly have all parts
needed to build a second Mendel, which I can use to try out alternative design
options.

My early impressions are that the J-head design extrudes more cleanly and
consistently than the Mendel-parts (V4) hot end, but is also slightly more prone
to stringing and oozing (not too seriously). I've noticed that I have the
extrude temperature set 10-15 degrees lower than with the Mendel-parts hot end,
and may go lower yet - I'm assuming this is in part because the J head design
has more efficient thermal transfer to the PLA filament, but of course
thermistor placement and calibration may be part of the difference here (their
thermistor is larger than the ones I was using previously).

#g
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