Inconsistent extruding from nozzle

[Niels_de_Kok]

Hello all! My name is Niels and i am a 3d printer newbie. I have watched tons of guides and tutorials on 3d printing. I suppose I spent around 20-30 hours doing that while building my printer.

I have a problem i can not seem to figure out and i can not really find on the internet. I did have a few other problems which i managed to solve on my own, including filament stripping, underextrusion and not perfectly level X-axis (Horrible noise).

My setup:

Prusa i3 - Steel, 12V, NEMA17, igus-drylin bearings, Ramps 1.4SB, DRV8825 drivers

Wade-style extruder, E3D V6 all-metal hotend (1.75mm), Mk3 aluminium heatbed. 0.3mm nozzle

Problem:

I am trying to print my PLA at the reccomended temperature of 220C on painters masking tape (yellow, cheap). The heatbed is at 50C (Worked better for adhesion than 60C). The print itself is a single walled upright bar, with bottom, no top. Layer height 0.2mm, speed 50 mm/s.

I observe gaps in extrusion, as shown in the picture. I see a nice steady stream of plastic flowing from the nozzle, and then suddenly nothing, and a little later it just continues. (In bad cases, when it continues it curls up at the nozzle and makes a mess, dragging everything along).

Diagnostics performed:

Simple extrusion through hotend in pronterface - 10 mm @ 100 mm/s occassionally hear a popping sound and see an irregularity (bump and decrease of flow) in the plastic stream, when extruding @ 10mm/s this becomes more pronounced.

Simple extrusion without hotend in pronterface - 100 mm @ 100 mm/s, perfectly extrudes 100mm of filament. (I did have to add about 20% steps/mm in Marlin to ~1950)

Tests:

Tried temperatures between 200-230 - No real difference

Tried extrusion multiplier between 100-110 - No real difference

Cleaned the barrel and nozzle very thoroughly with chloroform twice (Dissolves PLA) and used a toothbrush inbetween the two treatments. - No difference

Cleaned the hobbeld bolt with a toothpick and compressed air (was some slight grindings from skipping extruder from before) - No difference

I believe after spending about 10 hours on failed prints and searching for solutions on the net, i can say i honestly dont know what i could do more. (Except for maybe a extra extrusion test WITH hotend, although i did calibrate the extruder with the hotend before.)

Personally i suspect filament flexing/bending or snagging in the hotend barrel, getting softer/melted after a little while and releasing the pressure allowing for further extrusion. But as far as i know this should not happen.

Regards,

Niels

PS: I already typed all this etc, so i will add my pictures in a reply. Dont want to lose my text for whatever reason, haha!

[Niels_de_Kok]

The pictures, one shows a bottom layer with missing lines or gaps in the lines. (I was playing with the settings, so it seems a bit over extruded, and too hot)

The other picture shows my “towers” with decreasing temperature / extrusion multiplier towards the top.

Clear gaps visible in the extrusion path.

Note that the tape is bulging a bit, but that is because it looses adhesion after a while, it was flat when printing, i took this picture quite a bit later. (In the order of 2 hours or so.)

[Sra1]

Hi Niels, welcome!

At first glance, this could be caused by quite a number of things - I suspect this might be why there has been no replies yet.

Let’s start with the Filament - you mentioned popping, inconsistent volume, clogging at nozzle. This sounds like your filament has been exposed to moisture/humidity. It may be salvagable, some

people have successfully dried theirs in a cooking oven. It may be of poor quality and un-salvagable. So it may be cheaper/quicker to try another filament of the same material type (ABS/PLA) from a different supplier. Try a sample size if you dont want to commit to a 1kg spool.

Extruder - the steps per mm seem very high for a nema 17. Are you microstepping at 1/32? Of course it depends on your gear ratios, but standard is 1/16. I have similar motors and drivers, my E steps per mm is 420.

Next up is motor current - have you measured vRef across the DRV8825? This is done with a multimeter. The current is massively important, from what I read/see in your photo there’s a chance yours is under-powered and skipping steps.

Cooling - what are you doing for cooling? I dont mean the stock fan on the v6, I mean active cooling of the printed part.

Speed seem OK, 50 mm/s is reasonable.

Temperature 220 seems very high for PLA in my experience, but this is a contentious point and varies wildly with filament colour, manufacturer etc.

Build surface - you could try ditching the tape and trying PVA glue, as this is also cheap, quick and easy to try.

Let us know how you get on