CTC dual - PLA erratic extrusion difficulties, filament slipping on drive gear and/or stepper jerk

[jamesbe...@gmail.com]

About 3 weeks ago I bought a CTC dual 3D printer - the dual extruder one in black wood. I print by USB only from the computer as I'm fine with this for the moment and the SD card reader won't get fixed till I upgrade to sailfish anyway.

I'll spare you an epic history of how I got to where I am and all the things I've tried, but I have been doing a lot of reading and a lot of testing to try and improve things so suffice to say I've learnt a lot and done a fair bit of work myself before reaching out for assistance.

To sum up my issues they seem to be extrusion related and manifest by bad quality prints with gaps between layers, layers that separate/pull apart, bad looking infill and difficulty getting strings to bond/join on the solid infill layers. This is when it's at its worst but sometimes it does kind of print ok (although somewhere in the print there is a usually some sign of a flaw such as a small gap in side layers of a cube but only on one side. The quality is a bit erratic but I've noticed some settings seem to improve things (basically anything that slows down the extrusion rate eg. lower layer height, slower print speed).

The real issue I think I'm having appears to be either slipping of the drive gear against the filament or not slipping and the stepper/drive gear jerking back as it cannot push the filament but does not lose grip (eg. the current is too low on the stepper but there is no way to adjust the current as I believe they're digital pots). I'm only printing with PLA 1.75mm at this point.

I've replaced the original filament feeder with a printed one ( http://www.thingiverse.com/thing:231310 the v9) because the filament was slipping against the drive gear with the original which had no tensioner - I could literally only get something to print out by pushing the filament manually down into the filament feeder throughout the whole print. I used the grooved bearing from the original and put a strong spring in (I've tried numerous springs and if they're not strong the drive gear slips against the filament very easily).

I have turned the print speed down to 30mm/sec which seems more reliable (although is a pretty slow speed I think) and am prining at 215c with a layer height of 0.1mm (as this seems more reliable than 0.2mm). I believe this is due to the difficulty of the extruder to put out filament at anything other than a snails pace. I've tried different temperatures ranging from 195 to 230 and this seems to be the best for me. I've also tried increasing the print speeds and tried the range of 40-90 at 10mm increments but it didn't work - it would skip bits of each layer and the infill would look a mess. I don't think it can push plastic through the extruder well enough to go over about 30mm/s.

This morning I took the fan and heatsink off to observe the printing and saw the drive gear slipping against the filament again. So I took the nozzle off, cleaned out the PTFE insert tube and cleaned the nozzle (heating it very hot in a gas flame) after which I could see clearly through the nozzle. I also cleaned any shredded plastic off the drive gear. I put it all back together and the stepper clicks/jerks as it's printing, both on first layer and subsequent layers (printing 20mm test cube).

It's been a frustrating process and I have spent considerable time reading, printing, testing various settings. Currently I'm using the 7.5 firmware and Makerware slicer. I don't want to go to sailfish until I iron out these basic issues. I understand that Makerware 2.4 is the best to stick with for the moment (don't get the new versions) and that ReplicatorG is not the way to go. I really don't know where to go next but I'm fairly sure the issue is mechanical. I could get a new drive gear and/or filament feeder but then I suspect I'll be back to the clicking stepper that doesn't push the filament hard enough. I have tried using parts from the other head as well but this has not helped. I've tried the other stepper too as well as swapping the driver boards around for the two drivers on the mightyboard just in case there was an issue with one. I've also fitted a PTFE guide tube to help ensure the filament is guided into the head reliably.

It feels like either there is a blockage in the nozzle or other restriction - I rule this out because I cleaned out the nozzle today (and previously several times using different methods) as well as trying the nozzle from the other head or that the stepper is not powerful enough to push filament through properly a lot of the time. I don't know how I would fix the latter and I don't honestly believe that the original parts are that bad (not two of them especially, having tried both steppers from the two heads).

Someone please inject some sanity into my 3D printing world as I've about lost all of mine now. I think all I need to do is be able to get a solid grip on filament so it doesn't slip and be able to push it through the extruder at a reasonable temperature reliably at a modest speed (30 seems low but the fact that sometimes at that speed with the low extrusion rate used on 0.1mm layer height makes me think that this is really lower than it should do).

I have got through nearly 2KG of PLA now doing various tests and have a sea of test prints all over my desk. I've tried 2 or 3 different filaments to the one that came with the printer.

Thanks for reading to this point.

[ml...@rawebb.net]

Random thoughts... As I understand it, the toothed feed gear should almost never slip on the filament. If there's a jam beneath it or the filament is restrained above the gear then the filament should keep the feed gear from rotating and you'll get cogging from the stepper motor. The usual exception to this is when the feed gear teeth are clogged with filament and there's not much grip left but I'm sure that you've cleaned the teeth well (probably several times).

Is it possible that the idler pulley V-groove is too deep/wide? With everything cold, filament unloaded, and the heat sink out of the way so you can observe, poke an inch or so of fresh filament down past the feed gear and then try pulling it out. It shouldn't move.

[adam paul]

My .02$. Incorrect length for the ptfe tube. When you tighten the nozzle against the thermal barrier your compressing it.

https://groups.google.com/d/msg/3dprintertipstricksreviews/o8jX3RqdJ-0/641iCvV-srMJ

[jamesbe...@gmail.com]

On Wednesday, 2 March 2016 21:47:52 UTC, adam paul wrote:
> My .02$. Incorrect length for the ptfe tube. When you tighten the nozzle against the thermal barrier your compressing it.
>
> https://groups.google.com/d/msg/3dprintertipstricksreviews/o8jX3RqdJ-0/641iCvV-srMJ

I did measure the ptfe tube from the 2nd head before I used it (the first one got compressed between the nozzle and throat creating a disc shaped bulge in the middle and split) - the measured length of the 2nd was 33.62mm using my digital callipers. When I disassembled it all this morning there was no bulge in the middle - it didn't look compressed. I do have some replacement PTFE tube on the slow boat from china too.

I presume the implication here is deformation of the PTFE tube causing a difficult path for the filament. Would a photo of the PTFE tube in the nozzle help?

[jamesbe...@gmail.com]

On Wednesday, 2 March 2016 21:24:37 UTC, ml...@rawebb.net wrote:
> Random thoughts... As I understand it, the toothed feed gear should almost never slip on the filament. If there's a jam beneath it or the filament is restrained above the gear then the filament should keep the feed gear from rotating and you'll get cogging from the stepper motor. The usual exception to this is when the feed gear teeth are clogged with filament and there's not much grip left but I'm sure that you've cleaned the teeth well (probably several times).
>
> Is it possible that the idler pulley V-groove is too deep/wide? With everything cold, filament unloaded, and the heat sink out of the way so you can observe, poke an inch or so of fresh filament down past the feed gear and then try pulling it out. It shouldn't move.

It's possible the idler pulley is a problem for the slipping instances but then the same idler pulley can cause the stepper to cog/jerk so I just don't know. I have been thinking of getting an entire replacement filament feeder unit which would replace the one I've printed and come with spring and new bearing. I've also contemplated new drive cogs (I did buy one but it was a lot smaller diameter so presumably for a different MK drive).

I did take a video of it slipping this morning - I don't know an easy way to share that at the moment.

I've got a couple of photos of an object I printed tonight that I can see flaws in. I'll post them shortly.

[jbeeston]

These were printed tonight. I can't say I heard the steppers skipping but I wasn't in the same room for most of the print. Yet you can see signs of extrusion problems. And they don't seem to wrap uniformly around the object at the same layer.

I have tried numerous cooling solutions and haven't found the ideal one yet but currently have a 24v 40mm fan on a printed duct clipped onto the front of the print carriage controlled by the slicer (I added the mosfet and connector).

[jbeeston]

I just tried to remove it from the bed and it separated due to weak bonds between layers both at the back and front (different layers). Pictures show what I mean as well as the rather messy infill (I have had some cubes with a really nice looking infill but I don't know what is determining when it works well and when it looks messy).

[jbeeston]

Printing a single shell square wall has always been pretty reliable. Attached pictures show what seems to me to be reasonable quality aside from some temperature or bed adhesion issue on one corner (doesn't concern me).

I can pull on the sides and the layers do not separate.

I'm printing a 20mm test cube at the moment and I can hear the steppers skipping as it lays down the floor layers. I did have pillowing on the test cubes a lot initially but recently I increased the floor and roof heights up to 1mm and the biggest improvement by adjusting the direction of thos to 45 degrees instead of 90 so I get a lot more varying directions of plastic laid down. Pillowing is gone now.

There was no jerking at all with the attached square wall pictures and no apparent signs of under-extrusion either.

*EDIT* I should add that the MinLayerDuration setting is 10 seconds which on this type of print will slow down the head quite a lot more than the 30mm/s. At 30mm/s it only takes about 4 seconds to do each layer so with 10s min layer duration it's going to be going around half that speed so 15mm/sec which may explain why this object usually prints pretty reliably at 0.1mm layer height - very low rate of extrusion.

[jbeeston]

So I've been running at 0.1mm layer height and about 18mm speed and it's been printing pretty reliably. But this is pretty damn slow. My 2/3mm PTFE tube arrived so tonight I took some pictures of the old one and some measurements and cut a new one and fitted.

The old tubing doesn't look like i was compressed or incorrectly lengthed to me.Here's a couple of pictures of the tubing (for condition observation), inserted inside the nozzle and heat break. You can sse that there is no tubing visible when the nozzle and heat break are pushed together Also there is a picture of the tubing with caliper for the measurement.

[jbeeston]

Here's a picture of the new piece of PTFE tubing show with the caliper. I also took a few pictures of my extruder front front view and bottom view just in case it helps. The new tubing fits nicely inside the nozzle and break.

Printing after refitting I would say is just about the same as before, if not slightly worse. I'm printing a 20mm calibration cube at the moment and have heard several clicks of the extruder stepper.

I'm still not sure what's wrong. At the moment it feels like I'm doomed to just print at 1mm height and 10-15mm speed just to ensure it prints acceptably.

While I had the extruder apart I cleaned the toothed gear - it really wasn't too bad at all. I also tried pulling on the filament after feeding it with the steppers engaged and it didn't slip out. So the problem seems to just be that the stepper struggles to push filament through the nozzle at anything other than a snails pace.

[ml...@rawebb.net]

Is that PTFE tape on the nozzle and thermal tube threads? I can't quantify it but I'd speculate that is adding a layer of insulation between the aluminum hot end and the brass nozzle. May be that you're just not getting enough heat energy to the nozzle quickly enough (heat flux too low).

[jamesb...@gmail.com]

Yeah, I did put a little bit on the threads ages ago because I had a huge problem when I got the printer with plastic leaking out of both the top and bottom of the heater block and was dripping big blobs of molten plastic on prints. Since putting the PTFE tape on the thread it fixed all that although at this stage I'm not sure if there's even any tape left on the threads now.

The bit of tape on the heat break just above the threads I took off just after taking the photo so wasn't on when I refitted tonight.

Temperature wise I'm printing at 215c which has been working reasonably well so long as the speed is low.

[jamesb...@gmail.com]

I wonder if the filament is rubbing on the outlet hole in the bottom of the feeder block or if something is misaligned causing it not to move as freely as it should.

I don't really know how to test the stepper clicking issue either or to find the problem. I wonder if the 2 springs I'm using in the feeder mean the grip on the filament is too tight, but from memory it would slip a bit against the filament with just the stronger black one in there.

[rob evason]

This also happened to my CTC dual. I have been running mine for three or four months without problems and had nice print quality with PLA at a reasonable 198 degree hot end and variable on the heat bed. The erratic extrusion began after I ran out of the filament that came with the printer. Once I received my first replacement (Excelvan branded) I noticed the slipping cog sound and noticed visually that the PLA was a lot less viscous coming out so I increased the temperature but maxed out at 250 still with PLA that wasn’t melting enough. I deemed the roll to be bad and ordered an unbranded generic PLA, this next one was better I could print with it at around 239 degrees but it was extruding erratically, I could see the first line layer on the heat bed being drawn out fat then thinning out to nothing and getting fatter again, it would work fine if I assisted by manually holding and lightly forcing the filament into the extruder just like you explained, I printed out a spring loaded device this way but unfortunately still have the problem, I have tried several strengths of spring and feel the grip on the extruder gear to be sufficient, I have tried both filament in the other extruder which has not been used before (Dual) but it did exactly the same thing.  

[adam paul]

Increasing the heat that high most likely cooked PLA into your PTFE liner. This liner is a consumable item and will most likely have to be changed out. I have also found that much of the PTFE sold on eBay is PFA which is close but not quite as thermally stable, it breaks down much faster. You should buy some from a reputable source.

[rob evason]

I have been working on the printer and have found a solution to my erratic extrusion problem, which I attribute to varying filament diameter. I had tried the usual things like replacement nozzle and PTFE and upgrading the MK8 extruder to an MK9 with the spring loaded device. The reason it was still not extruding consistently was because the extruder fan heat sink was pushing against the spring loaded gear effectively clamping the pivoting arm and restricting its movement. This was noticed while observing the exposed drive gear in motion while the fan and heat sink were removed to inspect for slippage, there was no slippage it seemed to work normally. Modifying the unit to allow a gap between heat sink and pivoting arm worked. 

[adam paul]

That would indicate an assembly error. Every other extruder fits on that space. Was the heatsink on backwards? The fins should be out, with the flat back against the aluminum cooling bar. I have seen that issue of the heatsink pressing on the lever one time before, in the flashforge group, and that was the cause.

[rob evason]

The heatsink was fitted correctly but the 3d printed mk9 spring loaded device gave no clearance and I had to sand its surface down (about 0.5mm). A visual inspection of the heatink saw no warping or bend. After about 15 hours printing with nice results it started extruding erratically again after it ran out of filament and continued to print empty (possibly that could have affected the PTFE)

[adam paul]

Is it seated properly on the stepper? I think some photos here would be really helpful for us to help diagnose.