Extrusion rate drops after a few layers

[ppope357 0]

hi

I've been having problems with my prints, and have spent the last month or so trying to fix them without success. The problem is as follows:

The first few layers come out fine, generally to a good quality. But as the later layers print, the amount of PLA coming out of the extruder seems to reduce, resulting in blobby, stringy layers (see pic). The line of filament will be ok, then low volume, then normal again (over maybe a couple of mm of travel). this results in a layer that is only partly solid, kind of bitty. the next layer then doesn't lie on the previous layer, and the print fails. The problem seems to occur mainly for medium or larger prints - very small prints seem to work ok.

I tried replacing the PFA tube with a PTFE bowden tube, which helped a little. I made a new feed mecanism (berthos spring loaded/bearing feed mechanism to fix the filament against the hobbed bolt). That might have helped a little. It has cut down on the filament grinding that had been taking place. But the poor print quality persists.

I have been using netfabb to slice the models, with replicatorg 26. I've been using the high quality setting on netfabb - when I use the standard setting the problem gets worse (I think due to the higher speeds). Otherwise the replicator g settings are all standard. I have been using pla filament from faberdashery, which from past experience has been good quality.

Anyway, I would really appreciate some help or suggestions - I'm getting really sick of this problem. My printer did work really well for a few months, and was loads of fun - I really want to get it working properly again so print useful things.

many thanks[attachment=1]printfail.jpg[/attachment]

[joergen 2]

difficult to diagnose anything from this info.

generally, if the tube wasn't a bad one with bad ID, there was no need to replace it.

print failure after a couple of layers happens when you let the printer get too hot while letting it sit with heater on without printing, or by printing at a way too high temperature, causing the upper part of the brass tube getting too hot, and causing a plug of sorts.

lower the temp in 5 deg steps until the extrusion starts to look matte, not shiny any more. then increase your temp by 5 deg again, since that will be a nice print temp for low/med speed printing. and don't let the printer idle while hot for more than 1-2 min.

[ppope357 0]

thanks for your response.

The difference in friction when moving the pla down the bowden tube by hand was noticable - so I think the new tube probably did help a bit.

 

My printing temperature starts at 230 then drops to about 190, and in the past (when things were working well) these temperatures were fine.

I also try to avoid leaving the printer hot and idle, as I read somewhere this was bad for the printer.

If you let me know what further information would help with the diagnosis, I will dig it out.

thanks

[greengecko 8]

I had a similar experience. A great printer and then too less extruion after the first layer. Finally i found I had a plug in the hoted (only small but obviously enough to cause too much friction). So after cleaning i worked again. but I guess you have already checked when you changed your tube.

Another reason could be a too thin filament diameter. Can you meassure your filament? If so adjust the value to the slicer, but make you meassure it at more than 3 points. I also ad here some problems lately.

[ppope357 0]

many thanks greengecko, I will check for any fresh plugs in the hot end, and also measure the filament diameter.

[SandervG 1,521]

I would have suggested the same things, so i am looking forward to hear about your findings.

If you are experiencing a plug perhaps it is interesting to look into the new hot end V2.

Are you printing with different colours or only 1?

[joergen 2]

if you start your print too low (pressing the first layer of PLA too hard into the blue tape), you are creating too much pressure in the hot end, causing either grinding, or back flow of molten PLA up the brass tube, forming a plug when it's cold enough. if you start the print a tiny bit higher (1-4 clicks manually on the z axis), does it get better?

[ppope357 0]

many thanks for the responses. I am using a variety of colours of filament, which doesn't seem to make a difference. I have checked the filament diameter using some crappy calipers and it seems to be fairly constant - but due to the low quality calipers, I can't really be certain.

When I start a print, the print head is very close to the build platform, to the extent that the only sign of printing is a kind of "sheen" or shininess on the tape. The poor quality extrusion starts after 5-10 minutes or so. Would the back pressure cause a plug/blockage that would only manifest after this time? Anyway, I have screwed the build platform down a little, increasing the gap between the extruder and build platform a little.

I removed the bowden tube end, and between that and the peek insulator I found a doughnut shaped bit of pla. This must have been reducing the flow of pla into the extruder head, probably leading to the reduced extrusion. I removed it, refitted the bowden tube (getting it in contact with the peek insuator, as much as I could anyway), then screwed everything back together.

I'm doing a test print now, so will update with any progress.

I think I may have been suffering from a number of problems throughout this process. Initially, I think the original bowden tube was causing too much friction. Before I realised this, I changed the feed mechanism to berthos spring loaded system, and saw no real change. When I changed the bowden tube, the gouging of pla at the feed mechanism was pretty much eliminated - which indicates to me that the excess friction between the pla and the tube was causing the hobbed bolt to chew into the pla. The new bowden tube is a little too narrow (OD), which means it popped out a few times - I wrapped some tape around the end to widen it, and it has stayed in place so far. But possibly it is not clamped strongly enough.

anyway, we shall see. The test print will fail within the next 20 minutes, if I have not resolved the problem.

thanks again for your responses!

[joergen 2]

I removed the bowden tube end, and between that and the peek insulator I found a doughnut shaped bit of pla. This must have been reducing the flow of pla into the extruder head, probably leading to the reduced extrusion. I removed it, refitted the bowden tube (getting it in contact with the peek insuator, as much as I could anyway), then screwed everything back together.

that thing is called a plug, when the bowden separates from the peek due too much pressure from the filament (too fast, too cold, or no good transition. this has to be avoided under any circumstance.

 

which indicates to me that the excess friction between the pla and the tube was causing the hobbed bolt to chew into the pla. The new bowden tube is a little too narrow (OD), which means it popped out a few times - I wrapped some tape around the end to widen it, and it has stayed in place so far. But possibly it is not clamped strongly enough

unless the diameter of the filament doesn't match the bowden (filament around 2.9mm, bowden around 3.1mm), the bowden has no significant friction in this context, since it is made of teflon, and there is nothing more slippery than teflon (ask any gecko in your neighborhood).

the critical part the is the transition from bowden to brass tube, which needs to be tight, so no PLA can come in contact with the PEEK, which will be catastrophic. but if you make the transition too tight via the screws, the filament can't pass, and you still get a popping bowden. the filament really needs to get through the transition nice and easy.

[ppope357 0]

ok test over and another failure. I just pulled out another plug, so it looks to me like the fit of the bowden is incorrect, as you mention Joergen.

My original bowden tube was not teflon, but some other type of plastic with much more friction (I forget the name). I think the original tube was causing the friction and causing the hobbed bolt to chew the filament, distorting the pla an leading to more friction.

So from your advice it looks like now I need to improve that transition from bowden to peek. I've tried many times now to get the bowden tube snug onto the peek, and each time it isn't held in place. So what are my options now, any ideas? A new hot end and bowden might fix it, but I'm not sure if there are any other options. I'll try adding more tape to the bowden tube to fatten it within the clamp, but I don't think I can fit much more on without it becoming too fat to fit in the white holder thing. although that's going to have to wait until tomorrow.

Anyway, thanks for your help, it is much appreciated. I've been getting rather frustrated with the infernal thing, but I think I've made some good progress today in at least diagnosing the problem.

[joergen 2]

while of course the new hot end v2 is designed to prevent those events, it not really necessary to be able to print.

the fastest, and most secure way is the Joris M7 nut method:

1. get a M7 thread cutting die... borrow it from somebody, buy it cheap somewhere, it doesn't matter. if you can't get your hands on a M7, get a 1/4in. also, buy the corresponding nut (the flatter the better).

2. take out the white tube clip (always push the bowden towards the hot end through)

3. eyeball how deep the well in the peek is, and how tall the nut is, and thread at least 2-3mm more of the PFA tube with your M7 die... very easy done by hand, no tools.

4. thread the nut on the end, and feed the tubing upwards through the XY carriage (or the other way around, the nut will hold the tube against the bottom. if necessary add a washer.

5. make sure there is a bit more tube left below the nut to reach all the way into the peek.

6. chamfer the hotend side of the tube also a bit, to ensure a good seal around the brass tube, which should a tiny bit reach into the peek well.

7. heat up the hot end to 200-240C, and remove all PLA from the brass tube (the head dangles freely in the air, don't burn yourself). q-tips with paper sticks work great cleaning the brass tube inside.

8. let everything cool down

9. assemble the head according to instructions, but don't tighten the 4 screws

10. feed some filament through the tube by hand until you reach the PFA-brass interface

11. tighten the 4 screws carefully (alu needs to stay somewhat level), until you feel hat you are over tightening the 4 screws, and the filament doesn't pass easily through the interface

12. back off the 4 screws a bit, until the filament goes through easy again.

13. reassemble the rest, make sure the TC isn't broken or lost it's connection

14. warm to 100C and see if the TC is working properly

15. set your Z to about 1 sheet of paper thickness above the blue tape (your bed is perfectly level?)

16. start printing: your first layer needs to have about the same volume/space as all the following layers. adjust by hand for the first couple of prints, but keep count of the click (each one is 0.06mm) (find a z level adjuster on thingiverse to print, helps big time)

the purpose of the first layer is to offer adhesion to the blue tape, if you mush it too deep into the blue tape, your back to your initial problem, although you will more likely see grinding than popping. grinding needs to be avoided.

good luck

[ppope357 0]

thanks joergen for your detailed reply!

I have now managed to solve my popping problems, and my machine is working better than it has for months. I didn't use the method above however, I went for something a bit simpler. Gaffer tape (aka duck tape). I wrapped a little round the Bowden tube at the end, where it is clamped to the hot end. this increased the friction between the clamp and the tube enough that the thing stayed in place, for a while Anyway. I then printed out all the bits for Owens Bowden clamp, and kept on printing till the Bowden tube finally popped. when it popped I fitted the new clamp in place, and since then it has been working fine. the clamp comes with a spacer designed for a standard size Bowden tube, and I'm using a smaller one (6mm od ), and the standard spacer works fine.

so I now have a working machine, mainly due to Gaffer tape (Also due to the great advice above, much thanks!)

I love Gaffer tape.