J-Head MK-IV Hot End Clone Design

Got myself a J-Head MK-IV Hot End clone, from Ebay (snipermand), to see if it will be good enough to replace my heavily modified Mendel Parts Hotend V9 clone; and since the J-Head MK-IV is a clone, this is my quick review to share my purchase experience. The review also includes an illustration of how the different components fit together, how the J-Head clone stacks up against the original J-Head and conclude whether Hot End clones are really worth considering.

The J-Head MK-IV will be the third Hot End clone I’ve purchased in the last 12 months with the hope of putting together a decent extruder system for 1.75mm PLA filament. The Hot End I’m using right now is not as good as it should be and it’s a Mendel Parts V9, the first clone I purchased, which I had to heavily modify due to a manufacturing or design error made by the supplier in India. The second clone I purchased was the MBE Extruder V9 from qu-bd.com, and like for many other users, it just would not work with the 1.75mm PLA filament. This Hot End kit is a Makerbot Stepstruder clone.

J-Head MK-IV Hot End Clone Design

J-Head MK-IV Hot End Clone Illustration

The illustration above shows the clone version of the J-Head MK-IV Hot End and looks similar to the original J-Head supplied by hotends.com. The version I have is with the aluminium nozzle/heater combination which is also available in brass (J-Head MK-IV-B). The overall machining quality of this nozzle is very good and was delivered with the main components pre-assembled, and has some kind of red sealant locking the peek insulator on to the aluminium nozzle/heater. A resistor, thermistor and some wire was included, and also wire insulating PTFE tubing and bootlace ferrule connectors; which all needed assembly.

J-Head MK-IV Clone rear view, fitted to bracket with cooling fan

The peek nozzle holder has perhaps gone through the most evolutionary changes during the life of the J-head which demonstrates the importance of cooling; and version four is used here, but with only four vents instead of the five as per original design. The extra machining to the peek nozzle holder has greatly increased the surface area to allow heat to dissipate more efficiently to allow better cooling for extruding PLA filament. The series of vents round the peek nozzle holder would allow a cooling fan to be effective at lower RPM speeds making the 3d printer much quieter during operation.

The aluminium nozzle/heater combination that make the J-Head, is probably the best and most reliable 3d printer Hot End design in it’s price range. You have what is commonly three separate components (nozzle, heater block, threaded tube), combined into one. With the machining required to produce the nozzle and peek nozzle holder together, it still manages to be the best value for money Hot End out there; with the important good usage track record. The aluminium version I have is based on the blueprints for nozzle/heater combination version one.

J-Head MK-IV Converted to 1.75mm with PTFE Tube pushed down through the melt chamber to the nozzle tip.

PTFE liner tube is used in the peek nozzle holder which is held between the nozzle and the set screw under pressure. The design uses the PTFE tube to create a good seal between parts and also provide an almost instant transition from cold end to hot end for the filament path. The PTFE liner also provides some heat shielding from the peak nozzle holder as well as the nozzle itself, however, some active cooling would be required for PLA filament to prevent the PTFE liner from heating up too high. An extra PTFE tube was supplied as a method to convert the J-Head to a 1.75mm extruder from it’s native 3mm design; a method not supported in the J-Head Wiki because the melt chamber is machined for 3mm filament and not 1.75mm.

J-Head MK-IV Clone v J-Head MK-IV

If I’d done my research properly I might have decided to get the J-Head MK-IV from hotends.com instead of getting it from RepRap.me through Ebay. With the various clones available, you just can’t be sure that they’ve been manufactured using techniques that achieve the kind of precision and quality you would find in the original item. Basically, these Hot Ends are sent out to customers untested, and when ordering a clone Hot End, you are putting a lot of trust in the supplier, their understanding and knowledge of the product, and the quality of manufacturing.

J-Head MK-IV Clone. View of a Poorly drilled orifice that was claimed to be 0.4mm and turned out to be 0.5mm

Had I done some research on the J-Head MK-IV Hot End I would have realised that the 3mm to 1.75mm conversion method, applied to the J-Head clone, is not recommended. The conversion involved inserting another PTFE tube inside the existing PTFE liner; as shown in the above illustration. The PTFE tube is used to reduce the melt chamber diameter size to 2mm. It’s not clear how well this conversion performs or whether there are maintenance issues.

The 1.75 mm J-Head version from hotends.com would have a melt chamber machined for 1.75mm filament (rather than being reduced with PTFE tube from 3mm), which is likely to improve reliability over the Hot End clone version and have better control over to temperature in the melt chamber.

Hot End Purchase Experience

As I noted earlier, I’ve purchased three Hot End clones in the past 12 months with the third purchase being the J-Head MK-IV clone from RepRap.me via Ebay (snipermand). I ordered the J-Head MK-IV Hot End with a 0.4mm orifice and everything looked in order on delivery, the build quality looked good as far as I could tell and it seemed like I made a good purchase. However, while working on the J-Head, to get it ready for extruding, I kept noticing the Hot End orifice looking a bit big for 0.4mm. So I took some close up pictures with the nozzle tip up against a ruler and added some reference points to the Hot End nozzle images with an image editor. The image above right shows the grey reference points added.

The reference points on the image was used to accurately gauge the size of the Hot End orifice against the ruler, the orifice size appears to be 0.5mm in diameter. To confirm the size of the Hot End orifice I found an electronic component with 0.5mm leads, confirmed with calipers, and I was able to insert a lead into the orifice with a snug fit.

I’ve since sent a message to RepRap.me about the issue and still waiting for a reply. As it stands now I’m unlikely to use the nozzle since it does not meet the specification I wanted, and also unlikely to order another clone as this is the third clone failure to meet the specification claimed. Most people that order Hot Ends may not consider checking the nozzle size because the orifice is so small and take it on faith that they have been sent what they’ve ordered

Hot End Clone Conclusion

J-Head MK-IV Clone with Foil Wrapped Resistor

The J-Head MK-IV has few parts, but a lot can still go wrong through poor quality manufacturing and poor assembly. Things like poorly tapped screw threads, PTFE liner not retained properly, PTFE liner ends not cut squarely or cleanly, nozzle orifice drilled larger than specification, and assembly errors caused by lack of product knowledge. It only takes a single fault to cause the nozzle to fail and in view of this, it would be better to put your trust in the original designer and supplier.

All in all it was a bad decision to purchase this Hot End clone due to the lack of backing from the supplier. The sale campaign was mostly backed up with a copy and paste from the J-Head Wiki; with an added thermistor table for only the Sprinter firmware. The thermistor supplied had no brand or type to identify it and would be difficult for the less than average 3D printer user to set up correctly in firmware. Also, the supplier did not declare any working experience or manufacturing process to back-up the reliability or build quality of the their Hot End clone design.

A 3d printer Hot End is what makes a printer a 3d printer and so is a critical component that needs to be right. So the advice would be to buy your Hot Ends from the original designer and manufacturer that is backed up with good documentation and support. Basically, if you are out to buy a J-head Hot End, get the J-Head from hotends.com. Supporting the original designer/manufacturer/supplier will help with further Hot End research and development.

J-Head MK-IV Clone with PTFE Tube to convert Nozzle to 1.75mm	3D Printer MBE Extruder V9 from QU-BD. It could not extrude PLA filament with any success
J-Head MK-IV With Fan Mounted on Nozzle Bracket.	J-Head MK-IV Clone Hot End In Bracket with Bowden Push fitting

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