Hot End Design on 3D Printer Extruder

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.

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

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.

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.