Very low flowrate when printing

Hello.
I'm nearly done with my Prusa Mendel. I was just calibrating and running some test prints, when i encountered that my extruder didn't output filament fast enough. I'm using a bowden setup. I tried putting a smaller piece of filament directly into the hotend, not using the tube and motor. The filament was very hard to push through, even though the nozzle had preheated to 210 degrees celcius. I tried different thermistors, and different heaters, although that probably weren't the problem, it would have been an easy solve. It seemed that the filament didn't melt fast enough, because some got through, just very very little, and very slow. But 210 degrees should be enough for PLA.

Does any of you know what might be going on here?

Thanks

Double check your firmware settings to ensure you have the correct thermistor selected. Different types will have a different resistance at the same temperature, so it is possible you think you are printing at 210 when it is actually much cooler.

Make sure you are trying to print with ABS or PETG or some other type of plastic.

Double check that the thermistor is properly seated in the hot end and wired correctly.

Make sure the hot end isn't blocked or clogged.

Try increasing the temperature, or choosing different ntc setting in firmware. If you have a multimeter with thermocouple you can check if the ntc is giving the correct temperature. If not, you could adapt the temperature sensor table using the readings of the thermo couple.

When was still using my orginal hotends and bowden system I had similar issues.
Hobbed bolt constantly chewing filament or filament not being transported properly.
Especially when using big filament rolls towards their end the curling in the filament caused a lot of friction in the bowden tube.
But the bigget deal breaker was the hotends itself.
ABS was fine most of the time, PLA go stuck on a regular base.
In the original J-heads the teflon tube was going all the way through the hotend and secured by the bowden tube holder in the top.
This meant that it was next to impossible to hold the tube fully in place.
Once really hot telfon becmes a bit soft and flexible, enough in my case enough so the friction from filament caused the tube to be pushed silghtly into the nozzle part.
The more this happend the smalle the lower diameter became causing even more problems.
Until I reverted to a direct drive system I fixed the ssue by modifying the cold end.
I used a teflon tube with a bigger OD and tapped the top end of the cold end, the bottom part wa drilled out to the OD of the tube.
Took a bit of heating the teflon, swearing and a few cans of beer to screw the telfon tube into place and to cut it to the right lenght to moun the nozzle but worked a treat.

If you can try the manual filamet pushing again but without the cold end attached, if you still have problem pushing your nozzle might be partially blocked up.
Happens a lot with black flaments and those with added fillings, like copper fill, wood fill, glitter and so on.
When mainly printing PLA it can be enough to run some ABS at slightly too high temps trough to clean the goo and gunk out.
A good indicator of a partial block is that your printed filament looks stringy and the infill becomes extremely fine instead of being extra thick.

Edited 1 time(s). Last edit at 07/24/2015 09:16PM by Downunder35m.

Okay, so i just completely tore the hot end apart. It turns out that inside the the nozzle throat there is a small teflon tube. And when printing the filament would get retracted and would pull the teflon tube up, and partially out of the throat, creating quite a large area, in the buttom throat, that would have way more friction than with teflon. Combined with mixing temps, speeds of filament intake and more, it would result in a large piece of stuck PLA in the buttom of the throat, that just would get bigger, the more filament got pushed in. That was what caused it. Fortunately i had some spare teflon tube that i could use to make the whole throats length full of teflon tube. That way, there is no room for the filament to get stuck. I think i have solved it that way. We'll see

Thank you for your input