Under-extrusion on tall prints

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thedoble
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Under-extrusion on tall prints

Post by thedoble »

Hi folks

I thought I had this problem nailed but it appears not!

I've been trying to print this item for a 3dhubs customer, I've printed it 3 times now, and each time I've fixed a new problem. At this point, I'm out of ideas, it's so frustrating to have an 18 hour print fail right at the end :(

The problem is under-extrusion on the top 30% of the print. Some pictures:

Image

Image

As you can see, the bottom half of the print is solid, however the top half is very brittle - I could easily crush it with my fingers, or snap it off. There's gaps in the filament, like its only extruding at 1/4th the amount it should be.

Here's what I've done so far:

- Fixed bowden tube coming loose
- Reduced current to extruder stepper, and added a cooling fan. Stepper runs at room temp now.
- Fixed thermistor calibration - is now calibrated properly
- Reduced layerfan to 50% to prevent the hotend from losing temp during the print.
- Increased the strength of the tension spring on the ez-struder.

Where else can I look for problems?

Thanks
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Re: Under-extrusion on tall prints

Post by Glacian22 »

When the hotend is up higher, the filament has to take a more bendy path through the bowden tube, increasing friction. Meaning it needs more pressure to extrude. I'd guess that your extruder motor is getting overwhelmed at those upper areas. Are you running the stock ezstruder, or have you upgraded to some form of geared extruder?

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Re: Under-extrusion on tall prints

Post by thedoble »

Glacian22 wrote:When the hotend is up higher, the filament has to take a more bendy path through the bowden tube, increasing friction. Meaning it needs more pressure to extrude. I'd guess that your extruder motor is getting overwhelmed at those upper areas. Are you running the stock ezstruder, or have you upgraded to some form of geared extruder?


Thanks for your reply. That was my thinking too. I'm using the stock ezstruder. Should I be looking at upgrading?

I am a little miffed that the Rostock is sold as a 350mm high printer, when it will only reliably print up to 250mm :)
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Re: Under-extrusion on tall prints

Post by thedoble »

Another point - I recently switched to a different filament supplier. The filament I am using now is exactly 1.75mm in diameter. Previously, my filament was 1.66mm diameter. Is it possible that the thicker filament is causing more friction in the bowden?
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Re: Under-extrusion on tall prints

Post by Glacian22 »

That could be a factor for sure, and a little variance in diameter could be an issue too.

There are some good options for upgrades; if you want to pick up a geared nema 17 you can mod the ezstruder or use one of the designs based around that motor. Or if you're pressed for time to get that print done, you could print out a standard Greg's/Wade's style geared extruder from thingiverse. :)

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Re: Under-extrusion on tall prints

Post by IMBoring25 »

How long is your Bowden tube? Mine is such that, while I was building the machine, I had some serious question whether it was going to reach the entire build plate.

If that is the problem and you can get a sufficiently long Bowden tube, you also have the option of relocating the extruder drive above the top plate, which would allow more-relaxed bends near the top of the build volume and set you up a little better if you ever decide to go to a heated enclosure.

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Re: Under-extrusion on tall prints

Post by Windshadow »

I had no luck with the ninjaflex with the ezstruder
Then i got a Bondtech QR after reading Michael Hackney's review of it viewtopic.php?f=35&t=9446 viewtopic.php?f=35&t=9347
and the ninja flex prints with out problems so far with a flex bracelet I made... the BondTech is a very high quality kit so its easy to recommend, if a bit expensive, but how much time and plastic has the rabbit mask cost you... NOTE I have yet to print as high off the base as the ears of your mask so perhaps ask MHackney about that aspect. delivery from Sweden was very quick as well.

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Re: Under-extrusion on tall prints

Post by thedoble »

Glacian22 wrote:There are some good options for upgrades; if you want to pick up a geared nema 17 you can mod the ezstruder or use one of the designs based around that motor. Or if you're pressed for time to get that print done, you could print out a standard Greg's/Wade's style geared extruder from thingiverse. :)

Thanks for that direction, I didn't really know what to look for regarding upgrades. Right now I'm reading up on this one - http://www.thingiverse.com/thing:18379

The idea behind those upgrades seems to be gearing the motor to increase the torque. So the problem is the torque of the stepper? Not grip on the filament?
How does this effect the firmware? I assume at the least I would need to re-calibrate my steps-per-mm ... does anything else need to change?

Windshadow wrote:Then i got a Bondtech QR after reading Michael Hackney's review of it viewtopic.php?f=35&t=9446 viewtopic.php?f=35&t=9347

Yes I have seen the Bondtech, looks like a great piece of kit. You make a good point about wasted filament! But I think I'd prefer to try an upgrade that I can print myself first.
Last edited by thedoble on Thu Feb 25, 2016 10:33 pm, edited 2 times in total.
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Re: Under-extrusion on tall prints

Post by thedoble »

IMBoring25 wrote:How long is your Bowden tube? Mine is such that, while I was building the machine, I had some serious question whether it was going to reach the entire build plate.

If that is the problem and you can get a sufficiently long Bowden tube, you also have the option of relocating the extruder drive above the top plate, which would allow more-relaxed bends near the top of the build volume and set you up a little better if you ever decide to go to a heated enclosure.

My bowden is comfortably long enough to reach the entire build platform. When the effector is near the top, the bowden seems to curl around in a fairly relaxed fashion, however I see your point about moving the extruder to the very top.

Here's a pic of my current setup, with the effector placed roughly where it would have been upon completion of my failed print.

Image
Image
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Re: Under-extrusion on tall prints

Post by Glacian22 »

thedoble wrote:The idea behind those upgrades seems to be gearing the motor to increase the torque. So the problem is the torque of the stepper? Not grip on the filament?
How does this effect the firmware? I assume at the least I would need to re-calibrate my steps-per-mm ... does anything else need to change?


Right, it's the extruder motor itself that runs out of torque and starts skipping when it can't push through the friction of the bowden tube and backpressure from the hotend. By gearing it (either by using a planetary geared motor, or with printed gears) you're lowering the top speed (not an issue unless you want to print at 100mm/s with an e3d volcano) while increasing the available torque. For the firmware you're right again, you'll need to adjust the steps per mm to match your new setup, and you may find you need to adjust the amount of current going to the extruder motor, but it might be fine as is.

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Re: Under-extrusion on tall prints

Post by nebbian »

Another option is to use a flying extruder.

Here's one that I designed and have been running on my Kossel mini for a month or so:
http://www.thingiverse.com/thing:1259941

Image

This one should work with a variety of extruders, it just clamps to a NEMA 17 motor.

Flying extruders have many benefits, all to do with your bowden tube being a LOT shorter. A benefit in your case would be that there's no difference as far as the extruder is concerned, when you're printing near the build plate, or near the top of the envelope. A benefit that I've found is that there is a lot less "stored force" in the bowden tube, so changes in extrusion rate/printing speed don't carry over to subsequent operations.


Also, I've noticed that there are different bowden tubes out there... Some of them have an ID of 2.0mm, which is great for 1.75mm filament. Other stuff is closer to 1.8mm, which is not so great once your extruder gear has bitten great big teeth marks into the filament and smooshed it out of round. I've got 5 metres of bowden tube from RobotDigg which is useless, because it's ID is too small. Virgin filament goes through it OK, but once it's been through the extruder it is hard to push through the tube. Unfortunately there's no way to tell which stuff you're buying before you receive it and test it yourself.


Good luck sorting out your problem.

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Re: Under-extrusion on tall prints

Post by geneb »

Another thing to consider is that you may have turned the extruder drive down too far. Try bumping it a bit and see how that goes.

If you want to for-sure eliminate the "bowden drag" as an issue, you could try printing "higher". Make a stack of books or something on your printer to artificially reduce the build height - reset your Z zero point and you should be able to print PLA on cold glass - you'll need to tape the glass down to make sure it doesn't move on your stack of books. :)

BTW, I like the three-lobed extruder knob. Very nice!

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Re: Under-extrusion on tall prints

Post by cope413 »

I have a feeling it can be remedied without changing hardware.

What are your print speeds and retraction settings? Temps?

Does the part geometry get thinner as it goes up to the top of the ears?
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Re: Under-extrusion on tall prints

Post by thedoble »

cope413 wrote:I have a feeling it can be remedied without changing hardware.

What are your print speeds and retraction settings? Temps?

Does the part geometry get thinner as it goes up to the top of the ears?

The part doesn't really get much thinner toward the ears, the entire thing is about 10mm thick.

Settings are as follows:

#define MOTOR_CURRENT {150,150,150,130,0}
PLA, 195C, max 50mm/s print speed
Layerfan max 50%
4mm retraction at 30mm/s, z-lift ON 0.5mm, wipe OFF, coast ON 1mm
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Re: Under-extrusion on tall prints

Post by thedoble »

TLDR of my below post is as follows:
1. Stepper current too low - raised from 130 to 150.
2. Extruding too fast for hotend - e3dv6 LITE - reduced print speed from 50mm/s to 35mm/s.

Read on if you want the details!
------

geneb wrote:Another thing to consider is that you may have turned the extruder drive down too far. Try bumping it a bit and see how that goes.

This got me thinking - because I have been turning the extruder's current down - I thought it was overheating and causing the filament to slip. Originally it was at 165.
I ran some tests. I calculated my maximum mm/min as follows: (my math may be wrong here, but it seemed to work)

0.3mm layer height / 1.75mm filament = 0.1714
50mm/s max print speed is 3000mm/min
3000 x 0.1714 = 514.2mm/min maximum extrusion speed

So I plugged my printer in via USB, got the hot end up to temp and ran:
G1 E100 F514.2
The extruder skipped repeatedly when trying to extrude at this speed.

Next I re-loaded the firmware and increased my extruder current from 130 to 150.
Running the exact same test, the stepper still skipped, but far less often. I was able to run the extrude command over and over and it would only skip once in every 2 or 3 runs. The extruder stepper didn't seem to get hot running at the higher current.

This got me thinking about the limitations of my hot-end. E3D quote a print speed of 20-50mm/s on the v6 lite, so I started reducing my extrusion speed in GCode until I was able to consistently extrude with no skipping or slipping of the filament.

The number I came out with was F350 - which translates to 35mm/s maximum print speed at 0.3mm layer height.

This also got me thinking about my woes with stringing and trying to find the right amount of retraction. I am able to print a perfect retraction calibration test cube, but on larger objects, the stringing returns - the difference? speed! My smaller objects are automatically printed much slower for cooling's sake. (Seems obvious now!)

I believe my recent change of reducing the extruder current from 165 to 130 exacerbated the problem of the print speed being too high.

I have also gained an understanding of the factors involved in working out print speed. In the past it's been voodoo magic to me, but now I get it. I plan to write an explanation out that will maybe help others, as I have struggled with understanding how to work out how fast you should print for ages.
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Re: Under-extrusion on tall prints

Post by thedoble »

Well I am sad to say that the problem is not fixed.

I just re-ran the print with my aforementioned changes and had the same issue.

Image

I found that if I reduced the print speed to 8mm/s, the extruder seemed able to function again, but anything higher than this resulted in skipping and slipping of the filament. You can see the top half where the extrusion seems to be back to normal.
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Re: Under-extrusion on tall prints

Post by IMBoring25 »

I think I'd pass it M84 to disconnect the motors and try turning the extruder by hand while moving the effector around. If the resistance increases dramatically when the effector gets to the height where you're having trouble, it should be related to the Bowden tube routing. If it doesn't I'd think it's related to the timing or retraction patterns of that section of the print and would be looking at the hot end itself.

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Re: Under-extrusion on tall prints

Post by cope413 »

thedoble wrote:2. Extruding too fast for hotend - e3dv6 LITE - reduced print speed from 50mm/s to 35mm/s.


That's the issue. Your retraction is set to 4mm. With the E3D, you shouldn't be above 2-3mm with PLA.

My guess now is that you have more retractions at the top of the ears, so more chances to get the heat creep bulb that screws up your extrusion.

Set your retraction to 1.5mm and I would bet the problem is resolved.
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Re: Under-extrusion on tall prints

Post by thedoble »

IMBoring25 wrote:I think I'd pass it M84 to disconnect the motors and try turning the extruder by hand while moving the effector around. If the resistance increases dramatically when the effector gets to the height where you're having trouble, it should be related to the Bowden tube routing. If it doesn't I'd think it's related to the timing or retraction patterns of that section of the print and would be looking at the hot end itself.

I've tested at various heights and I can't measure any difference in resistance.

cope413 wrote:Set your retraction to 1.5mm and I would bet the problem is resolved.

I'll give this a go
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Re: Under-extrusion on tall prints

Post by thedoble »

OK I am beginning to suspect that my nozzle is clogged. This is with 1.5mm retraction:

Image

I have just switched to a new nozzle, will see if that solves things.
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Re: Under-extrusion on tall prints

Post by DeltaCon »

thedoble wrote:OK I am beginning to suspect that my nozzle is clogged.

If your nozzle is clogged, you would notice your filament slipping in the ezstruder. That usually makes a clicking sound and you can actually feel the filament going backwards after a pressure buildup. If that is not happening you probably have no clog. If you pull the lever on your ezstruder, you must be able to push down the filament without much resistance.
Yesterday a experienced a partial clog. Filament was still flowing, but it kept skipping in the extruder. I could hardly push the filament through the hotend manually. When I dismounted the nozzle the clog was visible, with a little hole in the middle that kept the filament more or less flowing. After burning the nozzle thoroughly with a dismantled gas solder iron the usual filament flow was restored.
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Re: Under-extrusion on tall prints

Post by thedoble »

Well the print with the new nozzle seemed to complete without issue, other than there being a lot of stringing - I ran the retraction at 1.5mm.

Image

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Re: Under-extrusion on tall prints

Post by Xenocrates »

At least it's done now, and you can use it. (Or send it off, I seem to recall it being for someone else), and use smaller towers to tweak it to get rid of stringing. Try playing with retract speed (Both slower and faster, many get good results with slower, but faster is the usually used first option), and travel speed (The higher the travel speed/acceleration, the less stringing you produce). I'm sure that with your usual attention to detail, you'll have it dialed in pretty quickly.
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Re: Under-extrusion on tall prints

Post by cope413 »

Yes, faster travel speed (175-200mm/s), and if you're using Z lift, stop if you can. Z lift just adds more time between retraction and subsequent extrusion, and time is the main reason for oozing/stringing. Even if the pressure is fully released from the melt zone, gravity is still in play and wants to pull that molten filament out and ruin your beautiful prints.
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