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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3D Printer Extruder Hot End Close Up

So, this is an introduction to my latest 3d printer extruder system with a detailed view of the Hot End, Cold End and Nozzle. There are plenty of pictures and a detailed illustration that shows details about the 3d printer extruder system I’m currently using. I explain some of the pros and cons, and explain why the latest extruder system I’m using works.

I’m still using a Twin Drive Extruder System I developed to push the 1.75mm Polylactic acid (PLA) filament into, what used to be, a very stubborn nozzle. However, forcing the filament into the nozzle was not the answer and some investigation work needed to be done to make the system work better. A new Hot End is purchased and after much tweaking, the extruder set-up is now working as well as it can be and I should be able to revert back to the single filament drive extruder upgrade, freeing up a stepper motor. I’ve got a new extruder stepper motor drive gear coming from the US which should provide improved grip on the filament giving more pushing power with a single stepper motor.

Airtripper’s 3D Printer Twin Drive Extruder

What was

The Hot End has caused the most frustrations and headaches during the 3d printer ownership, and at first, I was not sure if the Hot End was at fault or the fault was with some dodgy PLA filament. It seemed that some types of PLA filament extruded better than others, but I still had performance issues with them all. Rather than build a collection of PLA filament that failed to extrude, I decided to develop a set-up that was less fussy about extruding different PLA filament types.

After a number of different extruder mash-ups with some endless tweaking and putting new bits together, I finally have a 3d printer extruder system that works. Through tweaking, the Hot End part of the extruder has increased in sophistication due to having better nozzle heat control and active cold end cooling. This has allowed for better filament management during it’s journey through the 3D printer extruder system that is fitted to the Sumpod 3D Printer.

About The Hot End

A slightly altered version of Mendel-Parts V9

Where it’s from

My latest Hot End is a derivative of the Mendel Parts V9. The parts kit I got, shipped from Make Mendel in India, was supposed to be a Mendel Parts V9 copy, but there was an error in the main Peek housing that allowed the tubes to connect together without a thermal barrier between them, this meant the kit could not be used without a fix or part swap. Instead of returning the Hot End kit, I decided to use the parts to build my own derivative version.

How it works

The basic operation of the extruder system is to feed the filament, using a stepper motor drive gear, into the Hot End melt chamber to extrude melted plastic out of the nozzle tip. In order to achieve good extrusion performance for best 3d print quality, Some conditions in the 3d printer extruder system need to be controlled.

The Hot End has two chambers ( M6 threaded tubes), one melt chamber and one cold end chamber. The chambers are separated by a thermal barrier so that each chamber can be controlled to maintain separate temperature targets. The melt chamber is heated to the point where it melts the filament to a level that can be extruded with minimum pressure without the plastic burning. The cold end chamber, to avoid jamming, prevents the softening and swelling of the filament. A fan and heat sink is attached to the cold end chamber to keep the heat off the filament until the filament reaches the melt chamber. If the filament softens in the cold end chamber the filament will swell and become jammed under pressure from the extruder stepper motor drive gear.

Due to PLA’s relatively low glass transition temperature, the heat sink cooling fan needs to be switched on during 3d printing. Without the fan, the cold end becomes very hot which could lead to filament jamming. The Hot End is capable of extruding 1.75mm PLA at temperatures up to 230 degrees C without changing the glass transition of the plastic in the cold end.

3D Printer Nozzle Tube Parts with PTFE Tube Seperator

Hot End Pros and Cons

Pros

• 1.75mm PLA filament can be extruded at temperatures as high as 230 degrees C.
• The Hot End reaches the target temperature easily because heat transfer to the cold end is kept low by the PTFE thermal barrier.
• Filament swelling, causing extruder jamming, is prevented by using cold end heat sink and fan.
• M6 threaded cold end chamber allows for easy attachment to heat sink.

Cons

• The Hot End is difficult to assemble and has a lot of parts.
• The PTFE thermal barrier is difficult to get right because it deforms very easily, under pressure, when the M6 threaded tubes are screwed against it.
• The PTFE thermal barrier needs to be drilled on each assembly to align with the M6 threaded tubes. This causes extra wear on the inside of the tubes.
• The cooling fan adds extra noise to the 3d printer.

Conclusion

If I’d have got this Hot End from Mendel Parts instead of Make Mendel, I’m sure I would have had a few less problems. However, Make Mendel was the only company that had the parts and could deliver quickly.

1.75mm PLA is probably the most challenging Filament to extrude due to it’s relatively low glass transition temperature and of course being really thin as well. The Mendel Parts V9 Hot End derivative I created works well with this filament, and I’m sure Mendel Parts V9 original does work just as well if set up correctly. Anyway, working with a faulty Hot End has been very educational and has made me a bit wiser for my next purchase.

As it happens, I have a new Hot End on backorder, a Makerbot MK7/8 and Makergear Plastruder derivetive, so looking forword to getting that in the near future.

3D Printer Bowden Cable Extruder System	3D Printer Extruder Cold End with Fan Cooler
Sumpod 3D Printer Y Axis Top View	3D Printer Extruder Hot End Close Up
Old 3D Printer Extruder Nozzle with PTFE Tube Inner Lining.	Old 3D Printer Extruder Nozzle with Fan on SS Block Insulator

[bodyadsrich1l] More Hot End posts to follow as experiments continue, also a new belt driven gear stepper motor extruder is coming up.