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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 it’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. One thing that I have never been able to explain is that in all my printing with Nylon the J-head always seems to give better print results than any other nozzle I have used to-date. I do not know if it’s linked with the level of moisture in Nylon, or how the PTFE sleeve transports the material, or the level of compression, oozing or meltzone. I have a feeling it’s a combination of all these. So for Nylon I do prefer to use a J-head MK4/5 over anything else at the moment. Do watch out for cloned or badly manufactured J-head nozzles, I have had some during the year with various issues. Some requiring a massive amount of force to extrude, due to an incorrect machined nozzle hole length and others with sealing issues, incorrect use of materials and poor cooling capability giving a lot of oozing. Another interesting read for J-head background information is Brian’s J-head and ‘clone’ overview here.
Overall opinion and general recommendations 1. Best for Nylon Printing (245 Degrees C @ 30-80mm/Sec) (1.75mm recommended) 2. Good for general PLA printing (190-220 @ 10-80mm/sec) - Exceptional performance and print results at very low PLA temperatures down to 155 Degrees C. - needs active cooling of the PEEK 3. Do not overheat or the PEEK & PTFE can fail - Keep to under 250 Degrees, insulate the heater block. 4. ‘Industry standard’ Groove mount.