J-Head The J-head has been my default hotend for almost all my RepRap adventures, I have a lot of experience with it in almost all itâ€™s revisions and I still use them today in various models and adaptions. Recently we have seen an explosion of J-head like designs, some are built to the same or similar standard as the original design (hot-Ends.com) and others fall way short of being even slightly usable. J-heads do use multiple materials and tend to have more parts than other stainless or minimal designed hot-ends, but a well made and built J-head can run for years and process tens of Kg of material without any significant issues. They do have some limits and unfortunately people do tend to melt them more
often than you would expect (see above warning about cartridge heaters).
J-Head MK2 - Still a good and solid design, I have a stock of them that only run ABS, no external cooling required, extrusion speed is limited to around 40mm/sec, but they run ABS well at 245 Degrees C J-Head MK4 - Longer and heavier than the MK5 with similar printing performance. J-Head MK5 - Compact and very light weight, great for Bowden extruders running PLA, needs to be fan cooled for best results.
J-Head MK5 (dissassembled) four core parts - Nozzle is most often Brass, but can be machined in Aluminum too. REPRAPMAGAZINE