Brass nozzle too blunt causing drag-through?

I experience a lot of "drag through" when printing -- i.e. the previous layer hasn't cooled sufficiently and get's dragged around a bit by the extruder when it is laying-down the next layer. It is a problem with small areas because the plastic from the previous layer doesn't have time to cool before laying down the next.

I've partially resolved the problem using the "cool" plugin on skeinforge, but that will slow down the head only if an entire layer is small: if it is a large layer with localized small-areas the cool plugin doesn't help (really need a "localized" cool setting).

I've also tried using a fan to accelerate cooling of the layers. The problem with that is that it cools down the hot end too much so that extrusion fails. In other words, the hot end can't compensate for the cooling action of the fan. (I see a new hot end in my future most likely...)

Anyway, I'm thinking that the blunt tip on the brass nozzle of my extruder might also be to blame for some of the drag-through problem. I've noticed that many of the hot-ends I've seen on-line have sharper, or more pointed tips. I've included a photo of the nozzle from my machine. It seems that with mine, there is more "hot surface area" very close to the plastic that has been extruded. The more pointed tips I've seen on-line would only expose a very small point to the extruded plastic.

Has anyone found that replacing a blunt extruder nozzle with a more pointed nozzle improved their print quality, especially by reducing drag-through?

The "drag through" you're experiencing happens to me when the extruder isn't calibrated properly. It's extruding too much material and creates peaks that the extruder ploughs through.

This still happens slightly at the beginning of a print if my start z height is a tad too low, but corrects itself once the layers become mostly infill.

If you are experiencing this drag throughout the entire print, I would lower my e-steps/mm or increase the filament diameter in the dimension tab of skeinforge. You'll know you've got it right when the flat tops of prints are not rough nor concave.

BTW i used a modified version of the Mixshop hotend you posted for a few months and was able to make decent prints with it. I've since moved on to my own design with a pointed tip and more reliable extrusion.

Hi, i had 'Drag' to.I use smaller brass bolt Maybe M4 size drilled m5 size hole and retaped with M6 tread .Works much better

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canam
I've noticed that many of the hot-ends I've seen on-line have sharper, or more pointed tips.

The acorn-nut spherical profile, which is tangential to the orifice "die exit", is a less than ideal profile for an extrusion die.

The "die face", or "die lip" needs to have a flat plane orthogonal to the orifice axis.
A flat plane more readily balances the exiting forces of the extrudate internal shear forces,
whereas any small deviations of the spherical profile at the die exit will skew the exiting extrudate.

I'm guessing that a conical profile would be more advantageous than a bulges spherical profile.

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canam
I've also tried using a fan to accelerate cooling of the layers.
The problem with that is that it cools down the hot end too much

Try using a fan that shields the hot end.

Fan Duct for E3D hotend
(I like how this design has more room on the opposite side of the inlet to help balance the air flow.)
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