The small fan, 25x25mm, what does it do ?
Apart from cooling the (X ?) rod for the print head which gets the major part of the cooling wind there seems to be three possible targets:
The PEEK (heat insulator), but then it is a very strange location and angle for the fan.
The nozzle/heat element, but since there is a lot of energy put into heating it it does not seem reasonable to cool it down.
The heatbed, but some people (like me) installs heatbeds to keep the temperature up so why do you want to cool it down.
It seems the PEEK is the most likely answer after all but it leads to a new question; What controlls the fan ?
The only thermistor in the area, as I know of, is the one in the nozzle but is that controlling the fan as well ?
“The fan protects the PEEK part and helps to avoid that heat travels up, so we’d recommend not to turn it off during heating and printing.”
That´s one of the things i don´t understand in the construction of the printhead.
To protect the PEEK part from heat travels up it is much better to place a sheet of aluminium between the heater block and the peek part. Another benefit of this solution: The heater blocks are out of direct airstream of the fans and easily reach higher temparatures.
Also i can´t understand why the fans are connected to an output which is controllable by G-Code because of the danger to melt down the PEEK insulators.
Some people have problems to reach ABS printing temperature without slowing down the fans in slicer settings. If you do this you get an higher temperature and less PEEK part cooling at the same time. That´s not a very good idea in my opinion.
I changed these things (and some other) before first time printing other materials then PLA. No Problem to reach 250° degrees at nozzle and have a “cold” isolator guide at the same tiime.
And don´t forget: The 25mm fan in front reduces y-axis travel about 20mm.
Here are a few pics about the aluminium “heatshield”
The sheet fits exactly over the 10mm diameter part of the isolator guides and is hold in place by the hexagon of the nozzles. I covered it with kapton underneath but I think this is unnecessary.
@ SlowFoot: Don´t understand your Problem: The shield prevents the thread from overheating too because it covers it completely. The first 1.5mm are directly supported by the 10mm holes in the sheet and top side of shield is cooled very sufficient by the radial fan. To increase cooling power from radial fan I widened the opening in the extruder mount plate, took another radial fan and printed another fan guide to optimize the airstream. Another sheet of aluminium covers the openings of xy carriage 2 and I machined this part to guide the airstream from downside to front side to blow directly over the heatshield.
Here are a few more pics to explain:
Widened opening extruder mount plate
New fan guide
Machined xy carriage 1
Sheet to cover bottom of xy carriage 1
It is not a big problem to get these extra 20mm but you have to do this in marlin firmware in the configuration.h file but be careful to make changes there!
In order to access thhe extra millimeters I printed a fanguide for a 40mm fan on top.
Printhead test arrangement at work.
Additionally the most important point to me was to use the 2 fan outputs for the printhead fans instead of using fan 2 output for cooling the stepper drivers. As I found in marlin configuration_adv.h yo can easily turn the fan 2 output from stepper driver cooling to printhead cooling. So I decided to connect the stepper driver fan directly (over a temperature controller) to the power supply, extend the printhead wire loom with 2 more wires and connected them to fan 2 output and the radial fan.
Now the radial fan is controlled by firmware instead of g-code and its independent from the filament cooling fan. It starts with about half its possible speed if one of the nozzle temperatures reaches 50° C and works until both nozzle temperatures are under 50°C no matter if print job is finished.
The two bolts to fix the isolator guide are in row with the guide and they are rotated about 25 degrees. Distance from bolt to bolt is 22mm with isolator guide in the middle.
If you dimension it orthogonal you get these dimensions (nearly).
If the PLA is melting in the PTFE tube the heater must be too hot. Right temperature for PLA is about 190° (actual temperature is higher but the contact between the thermal sensor and the heat block is far from optimal) and I’m using 210° for ABS.
Thanks for the input.
I started having a closer look to the hotend inside design after struggling with stringing and clogged nozzle issues and because I was wondering why the filament got stuck in the extruder when unloading. I noticed that the pulled back filament has a thicker end (diameter ~2mm like PTFE tube inner diameter) which doesn’t allow the filament to pass the extruder when unloading.
So mcguivers approach with the heat shield seems very promising to me.
Earlier I did some trials with lower and higher temperature, different retraction values etc. but not very succesfully.
Nevertheless, the filament has still a thicker end (can not be unloaded) and - I’m afraid - will still tend to clogg the nozzle. Also I feel being close to the lower temperature limit so I will start to try installing a kind of heat shield. The more I look at the hotend design the less I can understand the concept of the fans blowing directly to the heat block…
Unloading filament always starts with pushing some through the nozzle then immediately pulling it back. I think this means the molten tip is still molten when it hits the PTFE tube end and so does not jam. I had this problem when the tip had charred debris inside and the PLA could not reach the hot tip well to get truly hot. I cleaned out the hot end by removing the tube, pushing a piece through with a bit of force, then pulling it out quickly and snipping off the melted end. Repeat this a few times; debris inside should stick to the PLA as you pull it up. Lower temperatures since then and no more clogs.
I thought I had found the problem. At a certain point I noticed I could print the fine structure object with printhead no.2 and only no.1 got clogged with the same object. After some systematic investigation I discovered that the fillament poulley was loose and after fixing this, the world seemed to be in order and I could print this thing on both nozzles withoug clogging.
However, now I tried a bigger 2h print - a simple tray, nothing complicated - and this time head no 2 clogged. Something is still wrong, I will try the cleaning you suggested and try the other side as well.