Slipping in extruder - no or low output

Yo rappers (ok, let's start this with some bad humour).

I have built a Mendel Prusa V2, and whilst having broken some plastic parts already, I'm confident in being able to make it work.

Now it moves in all directions quite freely, the heated bed got warm (once, then the MOSFET burnt out, need to get a new one and maybe fix some kind of heat sink).

But, the big problem for me is the extruder, I have a reel of ABS 3mm that I want to extrude through a Greg's accessible hinged Wade's geared extruder and a hotend looking like this: with a nozzle of 0.35 mm.

I don't know what I'm doing wrong, but it seems impossible to extrude through the hotend using this extruder, the hobbed bolt only slides on the ABS, creating sort of a fine dust and when I take out the ABS "rod" from the extruder it looks like someone has taken a big chunk right out of it, just at the point where the hobbed bolt comes into action. I have tested with different tempsettings on the hot end, to reduce the viscosity of the plastic, but nothing seems to help. The slipping effect is still there.

What do I do wrong here? If you want pictures, please tell me and I will get them ASAP for you.

Thank you for your answer!
Fizz out

does the extruder flow when feedstock pushed by hand, and is it possible the extruder is plugged? what temp are you extruding at?
pla is around 190-210, abs is around 210-250c. (if the hot end is supported by ptfe only then not above 230c)
and is your temp accurate, can you put your plastic feedstock against the outside nozzle and does it start to melt?

Hi jamesdanielv.

I love quick responses.

I aven't tested to push anything through the nozzle by hand, is it supposed to be very easy? I use ABS and I've tried from 190-300°C.

Didn't know about the max temp for ptfe, I maybe have damaged my hot-end. What do you think?

When I push the feedstock (better word than "rod", thanks) it does melt, but it doesn't become liquid, only soft and mushy. Is this a sign that the temperature is not ok? I have no thermometer, so I cannot check.

Hello fizzman,

I'm using the same hot end as you (just with 0.4mm nozzle) and just today I hooked it up to the x-carriage along with Greg's accessible extruder. I had tried pushing ABS through manually before and it did require more force than I thought it would, originally; but then again it is the first time in my life that I mess with thermoplastics in this context. Anyways, I tried running ABS filament today, motorised this time, through Pronterface and stumbled across the same issue as you, just that for me it was less persistent i.e. I would get 'micro jams' and the hobbed bolt would just be 'shaving' the ABS feedstock every say 10mm or so. The temperature of the hot end was always between 240-255 using thermistor setting 7 from Sprinter (I just picked it at random, don't judge).

After countless hours of diagnostics, I realised that our hot ends' melt zone is slightly larger than usual given that the brass actually runs up the 'barrel' quite a considerable amount when compared to say the J-Head hot end. What this means is that it will require a higher pressure to extrude filament (even more so ABS filament). There turned out to be an easy way to gain this extra pressure using the current setup. It was to tighten the screws/springs on the idler to their absolute maximum. Sadly this makes it more difficult to swap filament out, but you may always untighten them should you wish to change filament. Following the brutal tightening (as well a cleaning session of the hobbed bolt using a hobby knife) I was consistently extruding at 100mm/min 50mm multiples of filament without any trouble which I think is quite OK. A sign to show that the bearing is actually gripping the filament better is a small, yet distinct, 'line' down the center of the bearing i.e. the part which comes in contact with the filament.

Oh and also, make sure you tighten the hot end both with the supplied rods AND with M3 screws on the extruder's tapped holes as only like this will you be absolutely sure it won't ever budge due to the pressure it's under (since it uses PTFE as a support material, extra precautions have to be taken).

if the feedstock melts, then it is hot enough, and your heater is working at least within range. try pushing filament thru by hand. it may require some force, but if you can push it by hand then it will work with extruder. otherwise I would say the ptfe is deformed, meaning it may be time to upgrade. many people like the j head design because it is extremely forgiving.

Thank you all for your replies.

I have tried to push the feedstock through, and even though it demands some force, it is no problem to do it. So I'm guessing the hot end is ok...

It's my extruder gear that's messed up, I'll have to see if I can increase the gripping force a bit, as you suggest Pentatonic. I have also chosen the good thermistor (EPCOS 100k according to the supplier), I don't know if this has made a difference or not since I have no idea what was in the firmware before.

But now I'll be getting on with the extruder tweaking. Maybe the first part to extrude, if I ever get this to work, will be a new extruder...

Good evening to you all, and of course if I find something of interest to report I will write it here.
/Fizz

Ok. I think I found the problem(s).

There must have been a problem between the "push filament through by hand" test and the time I had reassembled the extruder. I think this comes from the calibration of the thermistor, as I stayed quite long times at high temperatures without pushing filament through the nozzle. There is some burnt material inside blocking the output.

Also, when disassembling the hot end, I found that the PTFE was a bit deformed, so I reopened the hole so that the ABS filament runs freely through.
However, it is still impossible to push the filament through the nozzle...

Tomorow I'm gonna pick up some acetone at the local hardware shop and see if I can dissolve the ABS overnight. Anyone's got an idea of how long time it usually takes to dissolve ABS? Especially in such a small nozzle (0.35 mm)?

Fizz out