Alternative Hotend.

Judging by a number of comments in the RepRap forum, some people are having problems with the longevity of J-head hotend.


* What are peoples experience with hotend's supplied in nopheads kit?
* As temperature seems to be part of the issue. How are people getting on printing ABS?
* Anybody attached an alternative hot end?
* E3D looks an interesting hotend, but needs an extra fan. Could one wire it in parallel with the existing cooling fan?

I have had more than one or two hotend blockages which I believe are down to the filament at the cool end of the JHead getting too hot and soft which leads to it being pushed out and solidifying in the gap around the top of the hex grub screw. I put this down to one thing - not enough flow (or is it feed?) of the filament through the JHead. That is, the filament moving too slowly and spending too long in the JHead itself. This will tend to occur during the first layer of a print when the head is at its slowest - more likely when a big surface area is being laid down requiring a lot of infill.

The solution - take care when printing items which will require a lot of time on the first, slow layer and if needs be, either speed things up at the slicer stage or be prepared to send an M220 Sxx command when the lengthy infill starts. The Mendel90 will print at quite high speeds anyway so it might even be worth experimenting with a view to speeding things up overall anyway to avoid the potential problem of a clogged up JHead.

Another thing to watch out for which will contribute to this problem is the extrusion temperature. I was having quite a problem with Faberdashery Jade Green when printing at my de-facto PLA temperature which is an indicated 220C on my Nophead Mendel90 kit. (Bear in mind that 1% tolerance thermistors are used in this kit and that Nophead's MARLIN temperature tables are based on temperatures obtained by measurement INSIDE the hotend nozzle using a thermocouple - they are as accurate as they can be). I cured the problems with the Jade Green filament by reducing the temperature by a massive 30C - at 220C it was flowing out like syrup but at 190C it extruded as it should. What I am getting around to is that if you print at too high a temperature for a specific flavour of PLA, the cool end getting too warm problem is more likely.

ABS is less likely to suffer from the above problem as it has a higher glass transition temperature - the heat which ends up at the cold end is not going to be enough to soften the filament to the same extent as PLA. The biggest problem I have had with ABS is delamination and to avoid that, I think that I will either need some form of enclosure as described by RichGain on his blog or else will have to wait for the hot summer days which MUST be just around the corner :-)

The ED3 hot end does look interesting doesn't it but if used on the Mendel90 kit as-is, will end up reducing the available print height and I suspect will mean that the carefully designed cooling fan shroud will just not fit. Don't forget that the fan in Nophead's kit is there to cool what is being printed not the hot end/JHead. As for wiring it up, it seems to me that the best plan of action in that regard would be to wire it in parallel with the heater resistor given that I don't think there is a permanent 12V line on the extruder PCB. I guess that in practice this may mean the fan turning on and off as the current to the heater cartridge goes on and off but I suspect that it will still work. If dispensing with the cooling fan, you could wire it to the cooling fan terminals, turn off cooling in the slicer and add an M106 to the start GCode, M107 to the end GCode.

Looking forward to comments from others on the above.

Alan

Edited 4 time(s). Last edit at 04/18/2013 03:57PM by Alzibiff.

To get permanent 12V you could take +12V from the un-switched heater connection and use the ground from the thermistor connection. It might add a bit of noise to the thermistor reading though or even cause a slight offset. Alternatively you could use the spare wire intended for a Z probe.

I use J-Heads on all my production machines with ABS at 250/255C and they run 24/7. They are very reliable. I did have a MK4 fail after about a year of continuous use. Somehow a round hole appeared in the side of the PTFE insulator about 2 or 3mm in diameter. That made it leak down the threads and unscrew itself. It still printed but the first layer height kept changing as it rotated.

I haven't had any problems with PLA jamming but I don't print it regularly although I did print quite a lot at the Manchester Maker Faire, but that was with a MK4.

A couple of customers have blown the end out by sending absolute E gcode when the firmware is configured for relative. Brian has explained in another thread that the thread is not as strong as it should be.

I don't get ABS de-laminating, even without a heated chamber as long as there isn't a cold draft. The only part of the Mendel90 kit I haven't tried printing without a chamber is the X motor end and that can be tricky even with a heated chamber.

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[www.hydraraptor.blogspot.com]

Im only printing PLA so far. My hotend did endure absolute E values during the setup of Cura without breaking.

But i had some blockages of the hotend while printing at layer heights below 0.3mm and while doing the first layer or having lots of retracts. Last week the brass part of the extruder popped out (i think i could have prevented it...).

I solved the problem by supplying the hotend with a minimal ammount of cooling. I cut two holes (~10mm^2) into the upper edge of the hole in the fan shoud and set the fan to allways on (S100 or ~40%). My heated bed ist set to 70°C to have the first layer stick nicely.


To reassemble the hotend i had to clean the threads in the PEEK and in the brass block. Heating it in the oven ~150°C made that an easy job. I had to remove the PTFE tape in the prozess and did not renew it. After assembly the length of the hotend increased by about 1mm but print quality didnt change. My backup JHead from reprapsource didnt get mounted yet as the other hotend works nicely.