The importance of nozzle tip design and drag.

Hi All

I seem to be having a problem nowadays in that my sparse infill tends to be very messy and the top layers always end up with holes in them.

It seems the nozzle tends to accumulate a little plastic on it (away from the hole) and this then causes the plastic the nozzle to pick up previous threads laid in the next pass (not layer but when the nozzle swings back on the adjacent strand).

I am not sure what changes I have made, but I do remember changing layer thickness from 0.35 to 0.33 and perimiter width over thickness ratio to 1.5 from 1.8 (to enable 2mm walls with an extra shell).

I am currently running a bunch of tests and upping the temperature (PLA) to 205 seems to be giving better results, but not good enough.

Is it better to have a nozzle tip that is a sharp point rather than a blunt point so that there is minimal opportunity for plastic to stich to the barrel and drag the newly laid stuff away?

If the nozzle is pulling stuff away something else is probably wrong.

How about some nice closeup pictures of the problem print and nozzle to help troubleshoot.

I'm guessing you have too much filament. Do you have the same problem with sparse infill? (60% or less)

What size is your nozzle? My experience with PLA is that sparse infill doesn't come out too well if you're layer thickness is smaller than 0.4 mm with a 0.5 mm nozzle. It doesn't seem to bridge across the infill gaps very well resulting in very thin filaments in the infill. This results in the top layers not being completely filled even though the sides and bottom are fine.

over time plastic actually will bake onto the extruder with a thin film.


A trick I use now is to lubricate the nozzle with oil on the outside. This makes it less likely to stick or stay sticking to the nozzle in any area.

if plastic crud accumulates on the outside of your nozzle, the plastic is like glue to other plastic, and will tear your build apart as the plastic will stick better to the hotter plastic on the nozzle.


With the nozzle heated, take a cotton cloth (no synthetics as they will melt) put some 3 in one oil on the cloth, and wipe away plastic crud, if anything remains, wire brush it or scrape it away with a screw driver. When finished, wipe down base of nozzle with oil.

This possibly is a reason that makerbot went with teflon coating on outside of there nozzles. as for nozzle designs, i think a flat bottom with a small surface area reduces drag and improves stringing issues.

Edited 4 time(s). Last edit at 08/02/2011 07:41PM by jamesdanielv.

I think the tip of the nozzle needs to be flat to a diameter slightly bigger than the widest filament you want to extrude and then slope away in a cone that matches the drill cone inside.

If plastic accumulates on the nozzle while it is extruding it generally means the flow rate is too high.

Interesting tip about using oil. I will give that a try.

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Hi James

That is interesting. I will give it a try.

I guess the oil film is so thin that it will not affect the adhesiveness of the layers being put down.

I did run a test putting my Perimiter Width Over Thickness (ratio) - PWOT - up to 1.8 from 1.5 and that seems to have improved the surface.

As brnrd states, my infil tends to be very messy (30% 0.5mm nozzle 0.33 layer thickness) with very thin strings between the contact points where a strand contacts the layer below. At the contact points it seems to be a bit bigger.

Out on the lash tonight so will run some further tests tomorrow...

On Wildseyed nozzles, which are copper MIG tips, I normally sharpen the tip to a point, and then I rap on it with a hammer which creates a flat area around the hole, and shrinks the hole to whatever size I want as well. For the most part, there is no stringing for PLA at temps above 205'C.

I,ve also made a few tips that were wide and convex, and they didn't seem to drag either, but then again, all my stuff seems to be more the exception than the rule here

I'm struggling with this same issue, as well, as I increase speeds above 40mm/s.

Won't Perimeter W/T only effect the perimeter paths? There's something similar under Fill, but i don't think it works exactly the same, since the skeinforge manual says to decrease the number if you get sparse infill.