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Ultimaker 2 Extruder problems - needed upgrade

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Hello,

 

I have Ultimaker 2 (standard, without "+") and I have big problems with extrusion with not standard material or with fast speed. I would like to make upgrade to Bondtech or trianglelab extruder. Please let me know if Bondtech is worth to pay 4x more than trianglelab? Or triangle lab is good enough? I would like to also know if I need to buy new stepper motor to extruder (from 2+) or stock from UM2 will be enough? I can not find anywhere this stepper to buy. Please let me know how to proceed with that. By the way upgrade kit official from Ultimaker is not good enough for my needs.

 

My second problem: very noise fan which is cooling heatblock - how and on what can I replace it? 

Thanks in advance for your support.

 

Best regards.

Remy

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Posted · Ultimaker 2 Extruder problems - needed upgrade

I recommend you get the bondtech DDG.  It's only about $95 or about 95 euros as well.

 

However if you are seeing lots of underextrusion, the problem is likely the teflon part.  You are supposed to replace that every 500 hours of printing or so.  Those are sold quite cheaply by Ultimaker resellers (unlike say inkjet printer manufacturers - Ultimaker does the opposite and keeps the price on consumables extra low).

 

I recommend you just get the teflon part.  And you should probably get an Olsson block while you are at it.  If you had the Olsson block you could remove the nozzle only and use a 3mm drill to widen the teflon a little bit which will make it last a few more days while you wait for the new teflon part to arrive.

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Hello,

 

I already replace this teflon part and I have olsson block. After cleaning is quite better, but I would like to replace the extruder. Do I need to buy motor from 2+? Or standard from UM2 is enough?

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Oh crap.  I'm completely confused.  You can't use the DDG with the UM2.  Only with the UM2+.  Sorry!  Everything is wrong - gear, mounting holes.  Sorry.

 

You can buy the bondtech QR extruder for UM2 - it costs a LOT more however and comes with its own stepper.  I'm not a huge fan of the QR because it's a pain to open (takes 20 seconds - yes I'm spoiled - but you'll be annoyed also) to slide filament in and out.

 

I personally have the medusa feeder on 2 of my printers.  But that's complicated.  If you have the time and want to save the most money - that's a great deal:

https://www.youmagine.com/designs/meduza-um2-belt-geared-feeder-improved

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

The "plus" kit from Ultimaker of course is awesome.  Upgrades your UM2 to a UM2+.  But it is something like 400 euros.  There is a chinese version much cheaper but I have no idea if it actually works or has serious flaws.

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Posted · Ultimaker 2 Extruder problems - needed upgrade
8 hours ago, gr5 said:

The "plus" kit from Ultimaker of course is awesome.  Upgrades your UM2 to a UM2+.  But it is something like 400 euros.  There is a chinese version much cheaper but I have no idea if it actually works or has serious flaws.

 

Yes I know, but I need only step motor to extruder from UM2+. Do you know where I can buy it? I found only motors to standard UM2, not +. Or maybe you know what is the specification of this motor? I am thinking if should I combine stepper motor from 2+ with bondtech or trianglelab, but probably I will choose cheaper trianglelab. 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

The UM2+ stepper has a different shaft than the UM2.  It also has a gear permanently mounted. You can order this part at a reasonable price from any Ultimaker reseller (you can order basically *any* part from *any* reseller as long as you know the part number - they don't list all the parts but they will sell them - but you will have to wait a while because UM ships to the reseller and then the reseller ships to you).  You can also get chinese versions of all these things at aliexpress.

 

The UM2+ stepper has no more power than the UM2 stepper.  They are the same torque.  Same power.  Same steps.  Different shaft.  The difference is that the "plus" feeder has 2X gearing to get twice the torque at half the speed.  This has nothing to do with the stepper. [correction - different number of steps - so maybe different torque - maybe same torque - don't know]

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Posted · Ultimaker 2 Extruder problems - needed upgrade
1 hour ago, gr5 said:

The UM2+ stepper has no more power than the UM2 stepper.  They are the same torque.  Same power.  Same steps.  Different shaft.  The difference is that the "plus" feeder has 2X gearing to get twice the torque at half the speed.  This has nothing to do with the stepper.

 

Ups - wait a minute...

The feeder motor for UM2+ and UM3 has 1.8° per step (200 steps/rev), and a gear reduction of 36:11  - while the UM2 feeder motor had 0.9° per step (400 steps/rev) and no gear reduction.

 

7 hours ago, remiol said:

I need only step motor to extruder from UM2+

 

part no.:  9470 (Feeder Motor Assembly)

 

@remiol where are you located? Here is a link in Europe (for example):

https://www.ideato3d.be/boutique/spare-parts/ultimaker-parts/ultimaker-2-parts/ultimaker-2-feeder-motor-assembly-9470/

 

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Thank you, I am from Poland, so I will need to find it locally. I will make a post in few days what I tried and results.

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Hello again,

 

I made many tests and trials on different material and I came to conlsuion that those defects which I had are coming from bad material, please look at below photos - what you you think? Everything is OK or you see some defects? Prints are very similar to my Ender 3 pro. 

 

I have other issue - I can not understand why machine dont retract always. Sometimes I see when distances are very long, but now always - it is coming from settting from cura - can you support me what should i change? 

My settings:

retraction distance 5mm

retraction speed 45mm/s

retraction at layer change - OFF

retraction minimum travel 0,8mm

retraction extra prime amount 0

maximum retraction count 100

max comb distance with no retract 30.

 

Attached photo with the problem on raspberry pi casing print - arrow places where should be retracted and machine does not do this. This wole line should be retracted! I dont know why machine is not doing this (and even not trying -I will hear jumping of the stepper). My ender is retracting this normally. 

image.png.136a7111693f37e2e879503dc9b3ad71.pngimage.thumb.png.a0dc5483b02979783071cb40cf94dad6.png

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Retraction (if enabled) doesn't work so well on the bottom layer because ideally you want to over-squish the bottom layer (so the part sticks well).  Which means there is always extra material leaking out.  The bigger question is if you print two columns how badly does it string from one column to the other.

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Posted · Ultimaker 2 Extruder problems - needed upgrade
On 4/27/2020 at 3:53 PM, tinkergnome said:

The feeder motor for UM2+ and UM3 has 1.8° per step (200 steps/rev), and a gear reduction of 36:11  - while the UM2 feeder motor had 0.9° per step (400 steps/rev) and no gear reduction.

Okay, thanks for the correction.  But you still can not put a "plus" feeder on a UM2.  And the gear reduction is in the feeder, not the stepper.  So buying only the stepper is useless as it has the wrong shaft.  You need the entire feeder.

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Posted · Ultimaker 2 Extruder problems - needed upgrade
4 minutes ago, gr5 said:

Retraction (if enabled) doesn't work so well on the bottom layer because ideally you want to over-squish the bottom layer (so the part sticks well).  Which means there is always extra material leaking out.  The bigger question is if you print two columns how badly does it string from one column to the other.

 

The same print on Ender 3 pro - retraction normally. Here I have the line which looks very bad. The same on the top layers, no retraction at all in few places. What should I change to enable retraction similar to Ender? I was trying to find all settings connected with retraction but now I have no idea how to solve it.

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade
2 hours ago, remiol said:

arrow places where should be retracted and machine does not do this

 

Looks like "combing" moves. Check the combing settings (section "Travel").

Set combing mode to "not in skin" or switch it off.

And check the travel moves in the Cura preview, moves with retraction are light blue. No need to waste material.

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Posted · Ultimaker 2 Extruder problems - needed upgrade
2 hours ago, tinkergnome said:

 

Looks like "combing" moves. Check the combing settings (section "Travel").

Set combing mode to "not in skin" or switch it off.

And check the travel moves in the Cura preview, moves with retraction are light blue. No need to waste material.

 

Thank you! it helped. 

 

Now I would like to know if those modification will be good for my UM2, or maybe you have other proposals what to change or something additional:

1. Fan bracket change for the same as in UM2+ - it will work? I recognized poor cooling. 

image.png.ec07144f95551f3b479c086f71bca60a.png

2. New fans for cooling print - the same as in stock UM2? after 1,6k hours i think that it will be good to replace both of them what do you think? Maybe you know better fans in this size?

 

3. New fan for hotend - replacemant for Sunon (stock is very, very noisy, massacre):

image.thumb.png.0794054453ded619157f399ca0b41b98.png

4. Last modification - bondtech extruder - maybe next month (expensive modification). With new motor from UM2+ (complete set from Bondtech).  

5. Touchscreen for Raspberry PI (now I have only rasp PI without touchscreen. I found it here: https://www.thingiverse.com/thing:2207689.

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

I don't have a feel for your budget.  If you don't mind spending 500 euros you should definitely get the plus upgrade kit.  If you are trying to save money, the two upgrades most worth it are the "plus" feeder (you can get a meduza upgrade for just $19 that's just as good in my opinion) and the olsson block.  The um2 fans are good enough in my opnion.

 

So I guess I need to know your budget.

 

Yes I like the quieter fan - I don't know the part number for the one UM used to sell with the UM2 the first year but it's very quiet.  I'm not sure the voltage of that fan either - did you check the voltage?  It's probably 5V but some of the fans are 12V.

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade
27 minutes ago, gr5 said:

I don't have a feel for your budget.  If you don't mind spending 500 euros you should definitely get the plus upgrade kit.  If you are trying to save money, the two upgrades most worth it are the "plus" feeder (you can get a meduza upgrade for just $19 that's just as good in my opinion) and the olsson block.  The um2 fans are good enough in my opnion.

 

So I guess I need to know your budget.

 

Yes I like the quieter fan - I don't know the part number for the one UM used to sell with the UM2 the first year but it's very quiet.  I'm not sure the voltage of that fan either - did you check the voltage?  It's probably 5V but some of the fans are 12V.

 

 

I dont want to spent much money, but if bondtech set is worth it, I can buy, but I expect perfect exxtrusion, on all my printers (chinese ender, cr10 and um2) I have problems with extrusion. My colleague told me that is much better than from UM2+, on bondtech he is able to print simple elements 120mm/s. What is your opinion? Did you try it? 

 

I am searching something to improve the cooling of the print due to fact that I have very poor overhangs near the bed (2cm above the bed is much, much better) - I print PLA with 60° on the bed. Did you have similar problems?  

 

I have olsson block, so I dont need upgrade "+". 

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

I have 5 um2 printers.  One has "plus" feeder, 2 have "medusa" feeder, 1 has original feeder, 1 has bondtech.

 

I like the medusa the best and it only cost $19.  I have characterized the pulling power off all these feeders and I don't have my notes in front of me but they go something like this:

original: 4kg

medusa with iroberti: 8kg

plus: 8kg

bondtech 10kg

 

This is (very rough - from memory) the amount of force (weight) that the feeder can lift if you only insert filament half way down the bowden.

 

I have printed thousands of hours on the "original" and it has enough force for me but there is definitely an improvement with the other feeders.  The extra power from the bondtech doesn't interest me and it's harder to slide filament in and out (the original feeder - you can't slide filament in and out at all - you have to use the menus).

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Posted · Ultimaker 2 Extruder problems - needed upgrade

So if you want to spend the least money for an excellent feeder, do the meduza.  If you don't mind spending 200 euros then get the bondtech - it's less work to install.  The meduza is quite a bit of work (printing all the parts and getting it all to fit together):

 

Instructions and links to all STL files.  The parts you need to order are all on the meduza page on youmagine (linked from page below):

http://gr5.org/med/

 

 

iroberti feeder (doesn't increase power but it's a great feeder!):

https://www.youmagine.com/designs/alternative-um2-feeder-version-two

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade
1 hour ago, gr5 said:

I have 5 um2 printers.  One has "plus" feeder, 2 have "medusa" feeder, 1 has original feeder, 1 has bondtech.

 

I like the medusa the best and it only cost $19.  I have characterized the pulling power off all these feeders and I don't have my notes in front of me but they go something like this:

original: 4kg

medusa with iroberti: 8kg

plus: 8kg

bondtech 10kg

 

This is (very rough - from memory) the amount of force (weight) that the feeder can lift if you only insert filament half way down the bowden.

 

I have printed thousands of hours on the "original" and it has enough force for me but there is definitely an improvement with the other feeders.  The extra power from the bondtech doesn't interest me and it's harder to slide filament in and out (the original feeder - you can't slide filament in and out at all - you have to use the menus).

 

Thank you very much for your info! I will think about this once again. What is max speed in mm/s on 0,4 nozzle and height 0,3? Are you able to achieve speed 120mm/s on bondtech or medusa?

 

Please only note that I see that my stock extruder does not have enough power - worned motor/extruder? I tried to put by octoprint 50mm extrusion, but I see (measured by calipper), filament moved less than 45mm on very low speed (on higher speed it is worse) - I can see that few milimeters extruder does not have enough power and filament was not moving always. 

Whats your opinion? When I print slow - all is OK. 

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

Steppers do not get old.  It's not the stepper.

 

With 4kg of force you can do about max 10mm^3/sec through a 0.4mm nozzle.  Bondtech I believe claims 18mm^3/sec with a 0.4mm nozzle.  Nozzles twice as large can pass about 4X material.  Nozzles 1.4X can pass about 2X material.

 

To calculate volume (I reported volumetric speeds - not linear), multiply line width (0.4 for 0.4 nozzle) by layer height by print speed.  for example 0.4mm nozzle with 0.3mm layer height with 40mm/sec print speed gives you (40 X 0.4 X 0.3) - I'll let you enter the numbers in a calculator for practice.

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Posted · Ultimaker 2 Extruder problems - needed upgrade

 

19 minutes ago, gr5 said:

Steppers do not get old.  It's not the stepper.

 

With 4kg of force you can do about max 10mm^3/sec through a 0.4mm nozzle.  Bondtech I believe claims 18mm^3/sec with a 0.4mm nozzle.  Nozzles twice as large can pass about 4X material.  Nozzles 1.4X can pass about 2X material.

 

To calculate volume (I reported volumetric speeds - not linear), multiply line width (0.4 for 0.4 nozzle) by layer height by print speed.  for example 0.4mm nozzle with 0.3mm layer height with 40mm/sec print speed gives you (40 X 0.4 X 0.3) - I'll let you enter the numbers in a calculator for practice.

 

Thanks for info, good to know. I have problems with 60mm/s, 0,4nozzle and 0,2 layer. Its 4,8mm3/s. When I am trying 0,1 layer, it is OK, but not with all materials. I am cleaning from time to time the nozzle with cold/hot pull. I had similar problems on ender 3 pro, solved by metal extruder for 5$. 

 

What is your opinion? What can be other root cause of under extrusion? I must print very slow to do not have under extrusion. 

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade
5 hours ago, remiol said:

What is your opinion? What can be other root cause of under extrusion? I must print very slow to do not have under extrusion. 

 

The PTFE coupler is a consumable and has a limited lifetime. This would be my first bet.

 

Some details:

https://ultimakernasupport.zendesk.com/hc/en-us/articles/115004429006-When-Should-Parts-Be-Replaced-

 

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Posted · Ultimaker 2 Extruder problems - needed upgrade
5 hours ago, tinkergnome said:

 

The PTFE coupler is a consumable and has a limited lifetime. This would be my first bet.

 

Some details:

https://ultimakernasupport.zendesk.com/hc/en-us/articles/115004429006-When-Should-Parts-Be-Replaced-

 

 

Person which sold me 3d printer replaced it during by presence.  Plastic tube was not bad as I remember, but tomorrow I will check once again. I dont know really what can be other issue than extruder... olsson block issue? I dont think so... 

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Posted · Ultimaker 2 Extruder problems - needed upgrade

CAUSES FOR UNDEREXTRUSION UM2 AND HOW TO TEST FOR THEM AND REMEDY THEM

One can quickly check the feeder (it takes seconds) so I would always do that first.  The feeder on UM2+ and UM2 can push with 10 pounds (5kg) force easily so first thing is to lift that lever (if um2+, if um2 regular do move material) and insert filament so it is only part way into the bowden (e.g. half way).  Then move the filament with "move material" command in menu so the feeder is energized and then pull down on the filament under the feeder.  You should be able to pull with 5 to 10 pounds force without it slipping.  Then have it move the material up while you pull down.  5 pounds force (2kg) is enough to make decent prints at moderate speeds listed below but you need 10 pounds (5kg) to print fast (e.g. 0.2mm layers and 60mm/sec)

As far as underextrusion causes - there's just so damn many.  none of the issues seem to cause more than 20% of problems so you need to know the top 5 issues to cover 75% of the possibilities and 1/4 people still won't have the right issue.  Some of the top issues:
1) Print slower and hotter!  Here are top recommended speeds for .2mm layers (twice as fast for .1mm layers) and .4mm nozzle:
20mm/sec at 200C
30mm/sec at 210C
40mm/sec at 225C
50mm/sec at 240C
The printer can do double these speeds but with huge difficulty and usually with a loss in part quality due to underextrusion.  Different colors print best at quite different temperatures and due to imperfect temp sensors, some printers print 10C cool so use these values as an initial starting guideline and if you are still underextruding try raising the temp.  But don't go over 240C with PLA.

2) Shell width confusion.  Shell width must be a multiple of nozzle size (in cura 15.X.  In cura 2.X it doesn't matter as much but still makes a difference).  For example if nozzle size is .4mm and shell width is 1mm cura will make the printer do 2 passes with .5mm line width which is possible but requires you to slow down much more to make a .5mm line out of a .4mm nozzle.  If you really want this then set nozzle size to .5mm so it's clear what you are asking Cura to do for you.

3) Isolator - this is most common if you've printed extra hot (>240C) for a few hours or regular temps (220C) for 500 hours.  It gets soft and compresses the filament under pressure.  It's the white part touching the heater block.  It's very hard to test when not under full pressure (spring and bowden) so sometimes it's best to just replace it.  Also if you notice parts of it are very soft (the blacker end where it touches higher heat) then it's too old and needs replacing.

4) Curved filament at end of spool - if you are past half way on spool, try a fresh spool as a test.

5) curved angle feeding into feeder - put the filament on the floor -makes a MASSIVE difference.

6) UM2 only: Head too tight?  Bizarrely MANY people loosen the 4 screws on the head by just a bit maybe 1/2 mm and suddenly they can print just fine!  Has to do with pressure on the white teflon isolator.
6b) UM2 only: Bowden pushing too hard - for the same reason you don't want the bowden pushing too hard on the isolator.
6c) Um2 only: Spring pushing too hard.  Although you want a gap you want as small as possible a gap between teflon isolator and steel isolator nut such that the spring is compressed as little as possible.

7) clogged nozzle - the number one problem of course - even if it seems clear.  There can be build up on the inside of the nozzle that only burning with a flame can turn to ash and remove.  Sometimes a grain of sand gets in there but that's more obvious (it just won't print).  Atomic method (cold pull) helps but occasionally you need to remove the entire heater block/nozzle assembly and use flame.  I found soaking with acetone does not help with caramelized pla. Even overnight.  Maybe it works on ABS though. Simpler cold pull: https://www.youtube.com/watch?v=u07m3HTNyEg

😎 Temp Sensor bad - even the good ones vary by +/- 5C and bad ones can be any amount off - they usually read high and a working sensor can (rarely) fail high slowly over time.  Meaning the sensor thinks you are at 220C but actually you are at 170C.  At 170C the plastic is so viscous it can barely get out of the nozzle.  You can verify your temp sensor using this simple video at youtube - on you tube search for this: mrZbX-SfftU

9) feeder spring issues - too tight, too loose.  On the black UM2 feeder you want the tension such that you can clearly see the diamond pattern biting into the filament.  You want to see at least 2 columns of diamonds.  4 columns is too much.  On the white UM2 plus and UM3 feeders you usually want the tension set in the center.

10) Other feeder issues, one of the nuts holding UM2 and UM3 together often interferes with the feeder motor tilting it enough so that it still works but not very well.  Other things that tilt the feeder motor, sleeve misaligned so it doesn't get a good grip.  Gunk clogging the mechanism in there.

11) Filament diameter too big - 3mm is too much.  3mm filament is usually 2.85mm nominal or sometimes 2.9mm +/- .05.  But some manufacturers (especially in china) make true 3.0mm filament with a tolerance of .1mm which is useless in an Ultimaker.  It will print for a few meters and then clog so tight in the bowden you will have to remove the bowden from both ends to get the filament out.  Throw that filament in the trash!  It will save you weeks of pain

11b) Something wedged in with the filament.  I was setting up 5 printers at once and ran filament change on all of them.  One was slowly moving the filament through the tube and was almost to the head when I pushed the button and it sped up and ground the filament badly.  I didn't think it was a problem and went ahead and printed something but there was a ground up spot followed by a flap of filament that  got jammed in the bowden tube.  Having the "plus" upgrade or using the IRobertI feeder helps you feel this with your hand by sliding the filament through the bowden a bit to see if it is stuck.

12) Hot weather.  If air is above 30C or even possibly 25C, the air temperature combined with the extruder temperature can soften the filament inside the feeder such that it is getting squeezed flat as it passes through the feeder - this is obvious as you can see the problem in the bowden.  The fix is to add a desk fan blowing on the back of the printer.  Not an issue on the UM3 or UM2 "plus" series.

13) Crimped bowden.  At least one person had an issue where the bowden was crimped a bit too much at the feeder end although the printer worked fine when new it eventually got worse and had underextrusion on random layers.  it's easy to pull the bowden out of the feeder end and examine it.

14) Worn Bowden.  After a lot of printing (or a little printing with abrasive filaments) the bowden resistance can be significant. It's easy to test by removing it completely from the machine and inserting some filament through it while one person holds it in the U shape.  Preferably i nsert filament that has the pattern from the feeder.

15) Small nozzle.  Rumor has it some of the .4mm nozzles are closer to .35mm.  Not sure if this is actually true.  I'm a bit skeptical but try a .6mm nozzle maybe.

16) CF filament.  The knurled sleeve in the extruder can get ground down smooth - particularly from carbon fill.  4 spools of CF will destroy not just nozzles but the knurled sleeve also.  Look at it visually where the filament touches the "pyramids".  Make sure the pyramids are sharp.

17) Hot feeder driver.  I've seen a more recent problem in the forums (>=2015) where people's stepper drivers get too hot - this is mostly a problem with the Z axis but also with the feeder.  The high temps means the driver appears to shut down for a well under a second - maybe there is a temp sensor built into the driver chip?  The solution from Ultimaker is that they lowered all the currents to their stepper drivers in the newer firmware.  Another solution is to remove the cover and use desk fan to get a tiny bit of air movement under there.  TinkerMarlin lets you set the currents from the menu system or you can send a gcode  to lower the current.  Ultimaker lowered the default currents in July of 2015 from 1300ma to 1200ma for X,Y,Z but left extruder at 1250. Other people (I think the support team of a major reseller but I forget) recommend X,Y,Z go down to 1000mA.

M907 E1250

Above sets the extruder max current to the default - 1250mA.  So try 900mA.  This will only change until next power cycle so if you like your new value and want to save it use M500.  You can just put these into an otherwise empty gcode file and "print" this and it will change.  Or get tinkergnome marlin!  You will wonder how you lived without it: https://github.com/TinkerGnome/Ultimaker2Marlin/releases

M907 E900
M500

18) third fan broken.  This tends to cause complete non-extrusion part way through a print.  In the rear of the head for UM2 and the front of the head for UM3.  Without this fan several things can go wrong.  It can take a while as usually you also need several retractions to carry the heat upwards.  There are a few failure mechanisms and I don't understand them all.  One of them is probably that the molten PLA spreads out above the teflon and sticks to the metal in a core or fills the gap at the base of the bowden in UM2.  Later it cools enough to keep the filament from moving up or down.

19) Spiralize/vase mode.  This is a rarely used feature of Cura but you might have left it on by accident?  In this mode the wall of your part is printed in a single pass.  So if you have a .4mm nozzle and the wall is .8mm thick it will try to over extrude by 2X.  This is difficult to do and may instead lead to underextrusion.

20) non-standard or bent fan shroud.  Sometimes people print some fan shroud off of thingiverse or youmagine out of PLA or ABS.  Some of these are great but most of them are crap.  One needs to do good air flow modeling.  Also if it's PLA it will slump and direct air differently.  Air directed at the block or nozzle can cause severe underextrusion and also sometimes HEATER ERROR.  Put the original shroud back on or just turn off the fan to prove that the fan is the problem.

21) Firmware settings - for example UM2+ firmware on UM2 or vice versa will cause 2X over extrusion or 2X underextrusion.  Downgrading or changing firmware can mess up steps/mm and other settings - so if you updated firmware and then problems started then do a "reset to factory settigns" which corrects all the steps/mm values.

22) too many retractions (this causes complete failure) - if you have too many retractions on the same piece of filament you can grind it to dust.  10 is usually safe.  20 is in the danger zone.  50 should guarantee failure.  You can tell cura to limit retractions to 10 per a given spot of filament.  Do this by setting "maximum retration count" to 10 and "minimum extrusion distance" to your retraction distance (4.5mm for UM2 and 6.5 for UM3 and 8mm for S5).

23) Brittle filament.  Espciallty with older PLA but even brand new pla can do this.  If you unspool some (for example if it's in the bowden) for many hours (e.g. 10 hours) it can get extremely brittle and it can snap off into multiple pieces in the bowden.  It's not obvious if you don't look for this.  Then it starts printing just fine and at some point one of those pieces reaches the print head and gets hung up somewhere and the printer suddenly stops extruding for now apparent reason.  This usually happens within the first meter of filament - once you get to printing the filament that was recently on the spool it should be fine from then on.

24) The "plus" feeder can have an issue where the filament doesn't sit properly for one print and it permanently damages the arm inside the feeder as shown by this photo - the hole is ground down asymetrically: http://gr5.org/plus_feeder_issue.jpg

25) Other feeder issues.  You can test the feeder by putting the filament only part way down the bowden and with the feeder electrically turned on (or moving) pull very hard on the filament until it slips.  You should be able to pull with about 5kg or 10 pounds of force before it slips.  4kg is acceptable.  2kg is a problem.  If the stepper motor isn't engaged you can try going into the move menu.  After a minute or so power is removed again from the feeder stepper.

26) Meduza - some people who install the Meduza feeder upgrade (2x the pushing power versus standard black UM2 feeder) make the belt so tight that the printer starts underextruding - typically as the circuitry heats up the extruder driver has less and less power and extrusion gets slowly worse over the course of 10 minutes or so.
 

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