Hot end throat blocks

Hi there!

I'm trying to build a 3D printer from scratch. For this I am testing the extruder hot end, and I can't seem to get it working properly.

The image attached gives my setup. I simply used a 0.4mm brass nozzle, a heating block and a nozzle throat. When I set the temp to about 200degC, and feed ABS, for about 10 sec, all goes well. (BTW I feed manually).

After 10 sec, I cannot feed anymore or very slowly. When I extract the filament, it seems that the filament already melts partly in the nozzle throat. This results in the blockage, as the partly molten polymer does not allow proper feeding anymore. On the image you can see that the tool can only be inserted for about 0.5cm. After that the partly molten polymer blocks all.

I have tried to add a heat exchanger block and a small fan to the nozzle throat, but this does not as well. The temperature of the heating block then also drops dramatically, having me to heat it even more with the same result as above...

The setup:
The above hot end setup
A 12V power supply
A P&ID to keep the temp at a setpoint

Should I increase even more the temperature?

Thanks!
Steph

Edited 1 time(s). Last edit at 08/02/2014 10:19AM by Stephanel.

Hi Stephanel,
It seems like your hot end's barrel is getting way too hot. The type of hot end that you are using requires a heat sink and a fan to actively cool the barrel. As long as the fan blows only on the heat sink, the heater block temperature shouldn't be affected too much. I made some DIY heat sinks from aluminum, and they work well for my hot end designs, which are similar to yours.
I would try running the hot end at around 230 C.

Edited 2 time(s). Last edit at 08/02/2014 04:15PM by 3D-ME.

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Agreed. 200c is too cold for ABS. I print at 230c-235c