PLA plugs above hot-end on UMO

[derek-bosch 1]

I purchased a used UMO about 4 months ago.  Everything was going great, printing solidly without issues

for a couple months.  Then I got my first filament jam.  I unblocked it (using the Atomic method, cleaned the nozzle, etc).  Since then, I've had very inconsistent results.

Sometimes it prints for 2-3 days without issue, but this past weekend it didn't last an hour.  

I'm using Gizmodorks 3mm filament (transparent blue), but I've also seen the issue w/ JET PLA orange.

printing at 210c.  using the most recent Cura (non-expert mode) normal print.  the design I'm printing is very

simple triangular bars - 5 of them lying parallel.

the plugs are right at the white teflon connector/ bowden tube... the filament gets ground down at the extrude wheel.

my experiments to try will be turning off retraction, as well as printing at a slightly lower temperature (200?)

I've taken apart the hot-end, cleaned out the white teflon connector, the PEEK, nozzle, etc.  Bowden tube is sitting flush in the white connector, and everything is nice and tight (at temperature).

Any other suggestions?  This has been very frustrating...

Edited June 8, 2015 by Guest

[Dim3nsioneer 557]

Make sure the Bowden tube sits really properly on the teflon coupler and the end of the Bowden tube is flat. Quite a good trick is to mount the print head but to wait with tightening the four long screws completely until the Bowden tube dits firmly in its place. You may also check if the Bowden clip holder grabs the tube nicely. Scratches on the tube at this spot are an indicator it does not. Finally make sure you never retract more than about 12mm on an UMO.

[jameshs 42]

plus some filament is worse than others and you might have to slightly UP the temperature. check the filament is consistent diameter (push a few lengths though the bowden.)

slightly tighten your feeder.

lightly oil the first metre of filament

each filament is different - I have some that blocks within 1 hour, and some that has never blocked. With the stuff that blocks I use it in my .65mm nozzle for 'prototypes' and use the non-clogging for 'fine' prints. (I mainly used colorfabb - and some old cf blocks, whereas the newer stuff tends not to).

[derek-bosch 1]

I reduced the temperature to 200C and reduced the retraction to 2mm, and it still jammed.

I will double check the filament diameter, but when I did so earlier, I found no sign of bumps or variation.

I will triple check the bowden tube -> teflon coupler connection.  I had done as dim3nsioneer suggested not tightening the long screws until the bowden is nice and tight.

What is the remedy if the clip holder DOESN'T hold the tube nicely?

I will also try increasing the temperature (to 220) to see if that makes any difference

Edited June 9, 2015 by Guest

[neotko 1,417]

Just a crazy idea. Are you sure that the bowden isn't inverted? I mean, the side that goes to the extruder has a different 'width' and it's a bit more open to allow easier filament load, but the side that goes to the hotend it's just plain 3mm.

[derek-bosch 1]

Just a crazy idea. Are you sure that the bowden isn't inverted? I mean, the side that goes to the extruder has a different 'width' and it's a bit more open to allow easier filament load, but the side that goes to the hotend it's just plain 3mm.

 

pretty sure it is the correct direction - the taped end is at the extrude end, the non-taped end goes into the teflon connector

[gr5 2,172]

I like around 4.5mm for retraction on UMO. I have printed lots of things at 240C no problem. If you are printing pretty fast then you need to print pretty hot. Here is a table of my recommended max speeds for different temperatures for PLA and at .2mm layers (.1mm layers print twice as fast):

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 usulaly with some grinding of the filament.

How tight is your spring - my spring on the feeder, when the filament is loaded and feeder is closed is 11mm and Simon's is 10.5mm.

Does your part have tons of retractions? For example if you have 1000 retractions all at 4.5mm then that is 4.5 meters of retractions. If you have 4.5 meters of filament that's not bad - about 1 retraction at every spot. But if you have 10 retractions or 100 retractions for every spot then you are likely to grind up your filament.

[derek-bosch 1]

I like around 4.5mm for retraction on UMO.  I have printed lots of things at 240C no problem.  If you are printing pretty fast then you need to print pretty hot.  Here is a table of my recommended max speeds for different temperatures for PLA and at .2mm layers (.1mm layers print twice as fast):

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 usulaly with some grinding of the filament.

How tight is your spring - my spring on the feeder, when the filament is loaded and feeder is closed is 11mm and Simon's is 10.5mm.

Does your part have tons of retractions?  For example if you have 1000 retractions all at 4.5mm then that is 4.5 meters of retractions.  If you have 4.5 meters of filament that's not bad - about 1 retraction at every spot.  But if you have 10 retractions or 100 retractions for every spot then you are likely to grind up your filament.

 

I'm running at 210 for 50mm/sec .1mm layers

not a lot of retractions, maybe 10 total per layer.

I need to double-check my spring tension when I get home.

Edited June 10, 2015 by Guest

[derek-bosch 1]

alas, running at 220 with no retraction still jammed after the first couple layers.

extrusion looks great up until it jams.

[gr5 2,172]

derek please update your country in your profile settings location field.

Could you please take a photo of your hot end from the side and post?

When it jams - how do you un-jam it? You said you used the atomic method to unjam it but can you explain more details? Maybe a photo of what it looks like when you pull the filament out.

>What is the remedy if the clip holder DOESN'T hold the tube nicely?

It's common for people not to hold down the tube-holder-clip when pulling out the bowden and it gets scraped such that it no longer holds well. Same parts for both UMO and UM2. If only the bowden is damaged just clip off 1 or 2 mm off the end of the bowden so the clip can hold a fresh spot on the bowden. However if one or more of the metal blades in the clip are bent or broken you should buy a new one. They are very cheap. I sell them but I only ship to NA. 3dsolex.com also sells them for a reasonable price.

[derek-bosch 1]

I will get a photo this evening.

As far as un-jamming it, usually I heat the unit to at least 90c, then pull the filament from near the spool (disabling the feeder wheel).

if that doesn't work, I end up removing the four long screws, pulling the nozzle/aluminum block off the teflon coupler, then push filament through the tube and cut off the plug that has formed...

Any advice in cutting the bowden tube? just a razor blade? or something more precise?

I will double check if I need a new tube-holder clip.

-Derek

[gr5 2,172]

You can tell if something is wrong because the bowden slowly slides up until there is an air gap easily visible when looking at the print head from the side.

Razor is fine - just make it very perpendicular and 2mm should be plenty - you can only take off 20mm or so before you need a new one (soon I will have some in my store gr5.org/store/).

Edited June 10, 2015 by Guest

[derek-bosch 1]

You can tell if something is wrong because the bowden slowly slides up until there is an air gap easily visible when looking at the print head from the side.

Razor is fine - just make it very perpendicular and 2mm should be plenty - you can only take off 20mm or so before you need a new one (soon I will have some in my store gr5.org/store/).

 

there is no visible air gap on between the bowden tube and the teflon connector...

I will get pictures later this evening

[derek-bosch 1]

 

You can tell if something is wrong because the bowden slowly slides up until there is an air gap easily visible when looking at the print head from the side.

Razor is fine - just make it very perpendicular and 2mm should be plenty - you can only take off 20mm or so before you need a new one (soon I will have some in my store gr5.org/store/).

 

there is no visible air gap on between the bowden tube and the teflon connector...

I will get pictures later this evening

 

no obvious air gap. the plug seems to be contained in the teflon connector. the peek and nozzle are empty of PLA.

I tried tightening the feeder spring to 11mm (it was over 13mm), and I trimmed 2mm off the bowden tube. Printed for about an hour and jammed again. I will try some different filament tonight

[neotko 1,417]

The curve that the bowden does even slightly it might be your problem. When you feed the filament by hand do you fell any tension before it goes out or it moves easy?

The S curve shows on the filament photo. It might be adding tension.

[derek-bosch 1]

it seems to move easily... not sure how representative the S curve on the filament was - I had pulled it out by hand, and might have put the bend in myself.

[gr5 2,172]

The feeder can push about 5kg or about 10 pounds. So the resistance in the bowden has to be at least 1 pound to be significant. Which is possible but I think unlikely.

I recommend you post these pictures over on the google groups forum - those people are more knowledgable for UMO issues (even though I have one and have used it for years - I never had this specific problem):

https://groups.google.com/forum/#!forum/ultimaker

[gr5 2,172]

By the way - did you have lots of retractions? didn't you already answer that? Sorry I didn't re-read everything. Each retraction moves heat upwards a little bit. Also longer retractions move it up faster. 4.5mm should be plenty.

Still I've never had this problem you describe. I'm thinking there is a tiny gap between bowden and teflon part. Did you put it together such that the 4 thumb screws are a few turns loose when you put the bowden in? You want the 4 screws loose by maybe 2 to 4 full turns and then lift on the bowden clip/holder while inserting the bowden. Then while still lifting, screw the 4 screws in slowly so the bowden is seated nicely onto the teflon. This will compress slightly any gaps that filament might flow into.

You know you got it right because then you no longer need the horseshoe shaped clip anymore - the force of the lifting bowden holds itself in place.

[gr5 2,172]

One more thing - I can't tell in your pictures but you want the threaded tube that is in the aluminum block and the peek to be low enough such that you can't screw the main nozzle quite all the way up to the aluminum block. If the nozzle is touching the aluminum block that is bad because it means you have another space for plastic to flow into and you are also more likely to get a PLA leak. Although I don't think this is your issue as any plastic flowing out will be molten in that area long before the nozzle is up to temp.

[derek-bosch 1]

By the way - did you have lots of retractions?  didn't you already answer that?  Sorry I didn't re-read everything.  Each retraction moves heat upwards a little bit.  Also longer retractions move it up faster.  4.5mm should be plenty.

Still I've never had this problem you describe.  I'm thinking there is a tiny gap between bowden and teflon part.  Did you put it together such that the 4 thumb screws are a few turns loose when you put the bowden in?  You want the 4 screws loose by maybe 2 to 4 full turns and then lift on the bowden clip/holder while inserting the bowden.  Then while still lifting, screw the 4 screws in slowly so the bowden is seated nicely onto the teflon.  This will compress slightly any gaps that filament might flow into.

You know you got it right because then you no longer need the horseshoe shaped clip anymore - the force of the lifting bowden holds itself in place.

 

I will try this when I unblock it tonight. And I will post in the google group as well.

Thanks for the help.

One more data-point... I'm about 75% through the current spool. Had no issues for the first 50-60%... I wonder if the bend on the filament near the center of the spool might be contributing at all...

And I completely turned off retractions... no improvement

[gr5 2,172]

int... I'm about 75% through the current spool

Definitely that can cause issues - but you can feel that when loading by hand. I still think it's getting in the gap between bowden and teflon.

[derek-bosch 1]

 

int... I'm about 75% through the current spool

Definitely that can cause issues - but you can feel that when loading by hand.  I still think it's getting in the gap between bowden and teflon.

 

me too, from when I take it apart. no plastic is in the peek or nozzle... just stops at the teflon

connector...

[derek-bosch 1]

One more thing - I can't tell in your pictures but you want the threaded tube that is in the aluminum block and the peek to be low enough such that you can't screw the main nozzle quite all the way up to the aluminum block.  If the nozzle is touching the aluminum block that is bad because it means you have another space for plastic to flow into and you are also more likely to get a PLA leak.  Although I don't think this is your issue as any plastic flowing out will be molten in that area long before the nozzle is up to temp.

 

I will double check this - I might have tightened the nozzle before I tightened the threaded tube... I assume both have to be done at hot temperature?

[neotko 1,417]

I fit everything so there's a 'less' than a milimiter of touching the aluminium (abit more) I fit it cold but without real force. Then when hot at 200 I hold the aluminium block and tight the nozzle (but not too much just a bit more). When I used the standard head I used to also hold the peek but that did over the change of 15 nozzles (4different ones a lot of times) I did end killing the alu block (so yeah don't over do it).

Btw did you try to atomic just in case? Just to remove the posibility...

[derek-bosch 1]

I fit everything so there's a 'less' than a milimiter of touching the aluminium (abit more) I fit it cold but without real force. Then when hot at 200 I hold the aluminium block and tight the nozzle (but not too much just a bit more). When I used the standard head I used to also hold the peek but that did over the change of 15 nozzles (4different ones a lot of times) I did end killing the alu block (so yeah don't over do it).

Btw did you try to atomic just in case? Just to remove the posibility...

 

I have done atomic pulls, both from the teflon connector / peak, and pulling all the way from the feeder