Part 4: Extruding Filament
If you managed to put together Extruder based on the previous posts, the next step is to extrude some filament.
Extrusion Temperature
I received a lot of questions about the extrusion temperature. Let me tell you for everyone this temperature is different as depends on the type of polymer, its specific composition, barrel material/thickness, ambient temperature, and many other parameters.
Remember we’ve 3 heating zones? The temperature of the first zone (near hopper) and the temperature of the third zone (near nozzle) must be equal.
The temperature of the second zone will be higher than the temperature of the first and third zone.
One thing to note is that the temperature reading on the PID controller screen is telling you the surface temperature of the place where the thermocouple is attached i.e. barrel wall. It’s not telling you the temperature of the polymer that’s inside the barrel. We are operating under the assumption that if we keep the temperature of the barrel wall constant then ideally, the temperature of the molten polymer will be constant. In reality, the temperature of the melt could be higher or lower than the barrel wall depending on the sheer applied to the polymer.
A good place to start our hit and trial method is this website, look at the cylinder temperature:
So, we set the temperature of zone 1 and 3 to 190*C and zone 2 to 200*C. Let the barrel reach the target temperature and stabilize for 5–10 minutes.
After that add the granules to the hopper and start the screw motor at the lowest RPM setting. When the filament starts coming out, try to pull the molten polymer with a pair of needle-nose pliers, you are looking for a chewing gum pulling like consistency. Lower the temperature if it’s too rubbery, increase the temperature if it doesn’t stretch at all. But by how much? Try changing temperature by 5*C at a time. You want the extruded filament to be slightly soft, not too rubbery.
Once you’ve got to this state, don’t worry if the filament is coming out to be too thick. We’ll stretch it into the right dimension and freeze it.
Freezing Die
Now, buy a 25mm x 25mm x 10mm cube of aluminum also buy a 1.75mm drill bit.
Drill 1.75mm hole to the other side along the 10mm side. There you go, you’ve your freeze die ready!
Water Bath
Filament exists the nozzles, goes inside a piece of bowden ptfe tube then goes into the aluminum freeze die which is submerged in a water bath at the start of the water bath then from the end of the water bath it goes into the filament feeder.
Now, you need a water bath:
I constructed one using MDF, I cut it with a jigsaw as I don’t have a circular saw. With some patience it’s possible, make it between 1 meter to 1.5 meters long, 6inch deep and 6inch wide. You also need to get a few aluminium hollow tubes and use it in the water bath to submerge the filament (white tubes in the above picture, you can use hard PTFE rod or tubes but aluminum tubes are easier to find so I used that). Also, aluminum tubes are easy to polish with mirror-like finish with a handheld drill and 1500 grit sandpaper.
You’ll fill the tank up to the cut in the front of the bath where filament enters the bath, the tubes will push the filament down below the water level to submerge it completely and remove the heat from the filament.
Once you’ve glued MDF like this, I used silicone sealant to waterproof the joints and latex paint everywhere else.
Manually pull the filament slowly in the water bath as the screw extrudes, don’t worry about the dimensions till now — it’s not important.
Filament Puller
After exiting the water bath, the filament will be solid just like the filament on store bought spools, so it will not be distorted by the puller where it bites into the filament and it will be stretched between the nozzle and freeze die — that’s what we want.
Once the filament is out at the other end of the water bath, all you need now is a puller:
Fix your printer to bench in front of the water bath, detach the Bowden tube from the hotend, disable cold extrusion in marlin and give it gcode to continuously extrude, feed your filament in the feeder and there you go!
All you’ve to do now is adjust the speed of the filament feeder, so it pulls the filament into the right consistency without filament pooling in the front of the freezing die. There is one sweet spot where you’ll get consistent filament within 0.03mm tolerance. If the filament is thicker than expected, increase feed rate of feeder/extruder through LCD, if it’s thinner decrease the feed rate.
What’s next?
This setup is good for extruding some filament but aluminium is a soft metal - it abrades fast and the drilled hole might enlarge, so after drilling the hole ream it a reamer and Hard Anodize it, it will make it harder than stainless steel, so it will not abrade: https://youtu.be/L2RKze7baJw , there are many process videos on YouTube for anodizing aluminium. Anodize it for longer to deposit a very thick layer of hard oxide, this will make it good for a few 100kg run! I’ve extruded 100kg+ and I see no signs of wear on freezing die.
As you can see we’ve done lots of hack jobs including putting our printer on line to get to this stage where we’ll be extruding sweet 1.75mm filament.
You’ve the filament extruder ready! The future step will be to remove the filament feeder from the printer or creating a new one (source the metal gear and stepper motor from aliexpress), you can either print one of the thingiverse filament feeder or buy a premade one — don’t buy the geared one like BMG for this purpose as it will drastically limit our pulling speed.
Buy a RAMPS board, write a firmware to control the feeder speed from a potentiometer and knob, and if you don’t know how then put the whole marlin on it and operate it as a 3d printer with missing parts.
Ofc, you can do it in a better way by improvising but why bother? I’ve managed to make 100kg+ filament with this hack job.
