Periodic under-extrusion issue on 300mm Voron 2.4 R2

[CallumRD1]

Printer Model

300mm Voron 2.4 R2

Extruder Type

Clockwork 2

Cooling Type

Stealthburner

Hi all,

I'm having an issue with periodic under extrusion and it's driving me nuts. I've attached a representative photo below. This issue occurs both on flats and on walls, with the under extruded parts causing structural failures in walls.

This is Polymaker ASA, printed at 250˚C, 260˚C, or 270˚C (with no appreciable difference between temperatures) on a 100˚C bed with a Dragon SF hot-end, ClockWork2 extruder, and 0.4mm nozzle. This happens for all flow rates I've tested, corresponding to 80-250 mm/s velocity at 0.4mm layer width and 0.2mm layer height (~6-18 mm^3/s). I'm printing enclosed with a chamber temperature of 50-60˚C.

In an attempt at resolving this issue I completely disassembled the extruder looking for faults but found none (granted I'm new to the ClockWork2 mechanism). The drive gear is not slipping on the filament or anything like that (although if I push flow rates to ~25mm^3/s it skips very violently!). Mesh between the drive gears appears to be good. The nozzle is clean and the hot end flows freely when I disconnect the ClockWork2 and feed filament by hand. I performed PID tuning on both the bed and hot-end with both managing to hold the target temperature to within ±0.3˚C for the entire print. Looking at the graphs of the PWM duty cycles don't show any systematic issues either.

I'm at a bit of a loss here. Nothing I've tried seems to make any difference. Can anyone help me diagnose this problem?

 

[Sanity Agathion]

In an attempt at resolving this issue I completely disassembled the extruder looking for faults but found none (granted I'm new to the ClockWork2 mechanism). The drive gear is not slipping on the filament or anything like that (although if I push flow rates to ~25mm^3/s it skips very violently!). Mesh between the drive gears appears to be good. The nozzle is clean and the hot end flows freely when I disconnect the ClockWork2 and feed filament by hand. I performed PID tuning on both the bed and hot-end with both managing to hold the target temperature to within ±0.3˚C for the entire print. Looking at the graphs of the PWM duty cycles don't show any systematic issues either.

Hello, I am not sure Dragon SF is capable of such high flow. Normally SF is around 14-15? maybe mm3/s, depending on temperature. Pushing it to 25 is even at the upper limit of Dragon HF without CHT at 0.4 mm nozzle.

 

[CallumRD1]

Hello, I am not sure Dragon SF is capable of such high flow. Normally SF is around 14-15? maybe mm3/s, depending on temperature. Pushing it to 25 is even at the upper limit of Dragon HF without CHT at 0.4 mm nozzle.

Yes, I'm well aware of that. I mentioned having skipping at 25 mm^3/s just to illustrate that I know what the skipping of the clockwork looks like when exceeding the hot-end's max flow rate. The print samples I'm testing and having issues with are from "80-250 mm/s velocity at 0.4mm layer width and 0.2mm layer height (~6-18 mm^3/s)", as I said in the post. I'm getting the same issues at 6 mm^3/s as at 18 mm^3/s, so that suggests that this isn't a hot-end issue but rather something in the ClockWork2 or somewhere else I haven't thought to look.

 

[Sanity Agathion]

Or could be a partial clog. That can demonstrate as periodic extrusion too.

If you suspect CW2, just in case check if is it assembled correctly, no gears are off axis, gear meshing between motor and 50T is set properly, if latch is not cracked, and the squish thingamajig and idler tension is set correctly. These videos may help: https://www.youtube.com/@dr.davesworkshop3585

 

[Bubbles]

check for just or debris in your drive gear filament channel
i had this issue once when my bmg gear filled up with clear petg dust.

drove me up the walls.

 

[bythorsthunder]

Lots of great tips here and you are right it is related to the extruder. Because it happens the same at high and low fédérâtes i would say ot is not a hotend, filament feed or other issue.

The most common possible causes in a CW2 are: 1. The gear mesh adjustment screw is too far out. This is the little m6 flat head cap screw. (This combined with minor eccentricity in the bmg gear set causes this exact pattern)
2. The grub screw on the bmg drive gear is too long or is not on the flat of the shaft. This results in the head of the grub pushing the drive gear away from the idler once a turn.
3. Significant eccentricity in the plastic bmg gear. This combined with an incorrect backlash between motor pinion and large plastic gear causes this issue.
4. Some combination of bad backlash , drive gears not aligned with filament path, drive gears plugged with gunk, worn out gears...
and probably some others that I can't think of at the moment.

 

[CallumRD1]

Lots of great tips here and you are right it is related to the extruder. Because it happens the same at high and low fédérâtes i would say ot is not a hotend, filament feed or other issue.

The most common possible causes in a CW2 are: 1. The gear mesh adjustment screw is too far out. This is the little m6 flat head cap screw. (This combined with minor eccentricity in the bmg gear set causes this exact pattern)
2. The grub screw on the bmg drive gear is too long or is not on the flat of the shaft. This results in the head of the grub pushing the drive gear away from the idler once a turn.
3. Significant eccentricity in the plastic bmg gear. This combined with an incorrect backlash between motor pinion and large plastic gear causes this issue.
4. Some combination of bad backlash , drive gears not aligned with filament path, drive gears plugged with gunk, worn out gears...
and probably some others that I can't think of at the moment.

This is very useful, thank you. This is a new build, with only about 1.5 kg of filament run through it, so everything is clean and sharp. I'll take it back apart tomorrow and check for eccentricities. That sounds like the most likely source of my problems. I was careful it setting my backlash but I didn't check it at multiple points of revolution, only at one given spot on the 50T gear. I have already completely removed the flat head screw that limits the maximum clamping of the idler onto the filament because I was worried that it was prematurely limiting my engagement on the filament.

 

[bythorsthunder]

This is very useful, thank you. This is a new build, with only about 1.5 kg of filament run through it, so everything is clean and sharp. I'll take it back apart tomorrow and check for eccentricities. That sounds like the most likely source of my problems. I was careful it setting my backlash but I didn't check it at multiple points of revolution, only at one given spot on the 50T gear. I have already completely removed the flat head screw that limits the maximum clamping of the idler onto the filament because I was worried that it was prematurely limiting my engagement on the filament.

Perfect approach. Yes it is important to check the backlash at multiple locations for sure. If it varies too much you'll need to replace, otherwise ensuring the closest point has no binding will likely be enough. If the extruder is removed you might even be able to spot the eccentricity as you manually pull filament through while latched. You can sometimes see the guidler moving in and out periodically.

 

[bythorsthunder]

Perfect approach. Yes it is important to check the backlash at multiple locations for sure. If it varies too much you'll need to replace, otherwise ensuring the closest point has no binding will likely be enough. If the extruder is removed you might even be able to spot the eccentricity as you manually pull filament through while latched. You can sometimes see the guidler moving in and out periodically.

This is very useful, thank you. This is a new build, with only about 1.5 kg of filament run through it, so everything is clean and sharp. I'll take it back apart tomorrow and check for eccentricities. That sounds like the most likely source of my problems. I was careful it setting my backlash but I didn't check it at multiple points of revolution, only at one given spot on the 50T gear. I have already completely removed the flat head screw that limits the maximum clamping of the idler onto the filament because I was worried that it was prematurely limiting my engagement on the filament.

Oh and also check the bearings. Ensure they are seated correctly and there are no rough spots as they rotate. I use a pencil inside and spin them. Also good to double check the needle bearings in the idler side are lubed up and running smoothly.

 

[CallumRD1]

Just closing the loop on this issue: I went through the ClockWork2 extruder with a fine toothed comb, even checking each moving part with an indicator and didn't find any obvious sources of the issue. The plastic 50T gear had about 8 thou of axial runout in it, but that shouldn't have made much difference. The only part I don't have much insight into was the stepper; I didn't have a replacement on hand to see if it was the source of the issue. So I decided to just bite the bullet and purchase an LDO Orbiter 2.0 and switch over to that. I installed it yesterday and the printer's been running non-stop since without a hiccup. I still don't know what was wrong with the ClockWork2, but I'm just happy to now have a printer running properly!

 

[Sanity Agathion]

Glad your printer is printing, even if the solution is not the cheapest. Sorry we were not able to give further advice :-(
Which mount for Orbiter 2 did you use?

 

[CallumRD1]

Glad your printer is printing, even if the solution is not the cheapest. Sorry we were not able to give further advice :-(
Which mount for Orbiter 2 did you use?

I used this one: https://github.com/elcrni/Voron-Mods/tree/main/Orbiter_2.0_SB_CW2_Enclosed

The tolerances on some of the holes seem slightly off, but nothing that a quick pass with a reamer couldn't fix. Other than that it's a really elegant mount, completely hiding the extruder and maintaining the StealthBurner aesthetic entirely.