In my previous post, I was indicating some factors as to why my print head was clogging as well as a description of the particular hardware being tested. I since have done some more accurate tests (and even taken notes!) to get a better picture of the factors involved with the print head.

I was under the misconception that not enough heat was the cause of some of my extrusion issues, so with my very shaky understanding of the properties of my unknown formula of ABS filament I was increasing the temperature to try to get a smoother flow. This was not the result, however. I was previously attempting to print with this plastic at about 240C and had pushed the hot end as high as 245C.

I started over again with the configuration, dismantling the hot-end from the cold-end of the extruder and testing by pushing the filament through the extruder using a metal tool and some filament stock at various temperatures. I slowly increased the temperature of the tip until I was able to consistently feed filament through the hot end. Using this method I was able to get a decent flow as long as the hot-end was at 225C. Although things started to move a bit at 220C, it required a lot of force to push the plastic slowly out of the .34mm nozzle – more force than I figured the extruder could push the filament without stripping it.

I cooled everything down and re-assembled the extruder before firing it back up again with this new lower temperature.

Once everything was back together again, I heated up the hot end and did some more tests with everything assembled, which is where a paradox with my setup comes into play. Even at the minimum-to-extrude temperature of 225C the x-carriage and extruder warp from the heat building up underneath it from the hot-end. This causes the weight of the stepper motor to pull the hot-end off-center as well as sag down towards the print. My experience with this scenario is that within a few layers the nozzle will start dragging into previously layers and starts getting pushed around by already printed plastic. I have never let it go for very long in this state as it looks very much like it is working at self-destruction.

I have machined and fit in an aluminum support plate underneath the extruder which improves the stability and heat dissipation, but not enough. I have found that a 50mm fan blowing upwards at the bottom of the x-carriage and across the extruder partially prevents this warping of the assembly even at fan speeds as low as 25%. The downside to this additional cooling is that it causes the ABS filament to cool too rapidly at the top of the melt-zone and it prevents the extruder from pushing the filament through. This happens even with the hot-end cranked up to close to 250C.

The only conclusion I can draw from this is that unless I find a way to keep the cold-end of the extruder cool without affecting the top of the hot-end, there is little chance of this printer handling ABS appropriately in it’s current configuration.

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