DIY filament extruder, half working, many questions

Hello to everyone on the rep rap forums. I am hoping that people here who know more than me on filament extrusion can help me with a project of mine, a DIY filament extruder, which has given me proof of concept, in that it melts plastic and begins to extrude it, but not with a very consistent diameter.
I will start from the beginning of my build and highlight any questions I have along the way.

So firstly, here I have a 12mm diameter auger bit, with a 12mm ID copper pipe to fit the auger, soldered to a 10mm ID copper pipe to fit the nozzle.


Next I cut a hole in the pipe, and begin to attach some sheet steel to form the intake hopper.



Then, through a combination of welding and soldering, I form a stand to attach this to a thick steel base, with a thrust bearing also mounted into the assembly. (I am not an experienced welder, so the welds don't look that great, but they hold well).



To heat the melt zone, I wrap nichrome wire around the copper pipe, obviously this would create a short if I did it directly, so I've had to wrap a layer of kapton tape around the copper pipe to electrically insulate it, then wind the nichrome wire, and then wrap another layer of kapton tape on top to keep things in place. A question I have is that, will the kapton tape inhibit the heat transfer into the pipe? Is there any way I can electrically insulate the copper pipe without thermally insulating it at the same time?

I then wrap fibreglass insulation around the whole thing and begin a test run.


I have not attached a motor yet, so I have a grip on the end of the auger bit to turn it by hand. This is definitely inconvenient, but I wanted to make sure I got everything else working first before I attached the motor, which I will do soon.

I am melting down HDPE from old milk jugs, because this is the plastic with the lowest melting point that I had on hand, at around 130c. The extruder struggles to reach above 150c so I think I need to improve my heating methodology before I attempt PLA or ABS.

Regardles, it does melt the HDPE, and it begins to extrude from the hole in the brass end cap.


But the diameter consistency is terrible and it looks more like it is taking a turd than producing filament.

I think that this may be because I am winding the auger by hand so the speed is inconsistent, once I attach a motor it may be better. Is there anything else I can do to improve the consistency?

For temperature control, I have rewired my Printrboard from my 3d printer, and connected two sections of nichrome wire on the melt zone as the "Extruder" and "Bed" with the appropriate thermistors wired also, one close to the end of the nozzle, and one near the hopper. I was careful to match the resistances of the nichrome wire to that of my bed and extruder. I can then control and monitor the temperature of the two zones through repetier.

I'm hoping some experienced builders will be on here and be able to offer me tips for improvements.

Thanks,
Karl

12mm leading into a 10mm bore is causing a pressure drop, and will take more force to operate, and it places the auger further away from the nozzle. This also increase the amount of resin in compression (it's a spring), and will cause some diameter variation. I would think that you would want to terminate the auger at the face of the nozzle. Grind the end of the auger flat. I would probably weld on a cap to the barrel, tap it to accept threaded nozzles so you can easily change out orifice diameters for experimentation.

If you have a drill with enough torque, and variable speed, use a hose clamp to adjust the rpm for experimentation, and operate in reverse.

Purchase fiberglass braided sleeving, and thread your nichrome wire into it for electrical insulation. Probably going to be a PITA, so consider use a few band heaters.

Looks cool, what will you drive it with?

Thanks for your help.
Yes, the reason I used a 12mm pipe at one end and a 10mm at the other is that I had a 12mm auger but only a 10mm brass fitting to screw the end stop into.
I didn't mention it in the first post but I have already cut the end of the auger flat due to problems with the pipe clogging.
I understand what you mean about the pressure drop, I can imagine some of the plastic having friction with the edge as it transfers from the 12mm to 10mm pipe and that's probably what was causing part of my clogging issues also.
I will take out the 10mm pipe, solder on a section of 12mm pipe and terminate the nozzle closer to the hopper. I reckon I'll be able to weld the 10mm brass fitting into the 12mm pipe and fill in the extra gap with careful welding/soldering.
Hopefully a shorter barrel will mean that the windings for my nichrome wire will be compressed in a smaller space and probably allow me to achieve higher temperatures. A quick search for fibreglass braided sleeving on ebay looks like expensive stuff, but I'll see if any local stores do it.

I don't have a drill with variable speed, but I do have an old tread mill motor which I intend to use to drive this, not sure whether geared or direct drive yet. Looking at PWM controllers on ebay, this seems up to the job to give me speed control: [www.ebay.co.uk]

I'll keep you updated

I forgot how big my treadmill motor was! I'ts as big as the extruder itself! It may be overkill for this project, but considering I got it for free (a friend was throwing away the treadmill) I might aswell use it.
At 12v I get about 100rpm and it gives shed loads of torque so I'll have no need for gearing. Just a PWM for speed control.

Treadmill motor, I like it, too bad you don't have the rest of the treadmill for the electrical.

The duct tape coupler is awesome

haha, the motor is not coupled yet, what you can see there is a few blocks of wood superglued to the end of the auger bit with duct tape around it to provide grip for hand turning. The motor is just lying next to it for demonstration
I will build a proper coupling and a frame to secure the motor once I have shortened the barrel.

Hi, an update from the last week is that I now have the treadmill motor coupled to the auger bit. 12V from the PC power supply is more than enough for it and it has enough torque to operate direct drive (yay, no messing about with gearing ). I received a PWM controller a few days ago to control the speed of it, most of the time it only needs around half power.
I shortened the barrell to remove the 10mm section and things are better. I can achieve 200c max and the diameter of the filament is much more consistent but not perfect.
I have managed to extrude HDPE and PLA but cannot get things hot enough to extrude ABS.
For heating, I have wrapped two lengths of nichrome wire around the barrel, 7.5 ohms each, electrically insulated using kapton tape, and thermally insulated using fibreglass insulation. Connected the lengths of nichrome wire to the 12v outputs of my printrboard, one connected to the bed output and one to the hot end output.
Since the hopper is also made from steel, it conducts heat away from the barrel. To try and achieve hotter temperatures, I am encasing the entire outside of the barrel and hopper in fire cement to hopefully give better thermal insulation. I am also shortening the nichrome wire to 6 ohms. Less ohms means more watts and more heat so hopefully these two improvements will help me to achieve ABS melting temperatures.
Does anyone know how low I can go on the resistance of the heating element without smoking my printrboard? Do they have overcurrent protection?
Only have enough time for one photo at the moment, you can see the fire cement covers most of the barrel and hopper, the front section has not been covered as I will wind that with nichrome wire and then encase that with fire cement. The steel base plate and supports have also been given a nice coat of red paint to prevent rust and to look better

You can also see the section of copper pipe at the front for the extruded filament to rest on as it cools. This helps but I'm still not getting consistent filament diameter. Once I've rewound the barrel with new nichrome wire I'll concentrate more on the diameter consistency problems. At least at the moment it is good enough to convert shredded plastic to pellets by chopping the extruded filament!