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Roaldo

Destroyed 2 cores with printing error

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Hello all,

 

I use a Ultimaker 3 extended at my workspace for almost a year now. Never had any kind of problems with it untill last week. I came into work on a morning only to see that the ABS had built up inside the nozzle head. I don't have a clue why and how this could happen. The printer was printing overnight.

I attached some photos because they say more than a 1000 words. I used the correct nozzle: AA. This print was only using the right side AA nozzle. I used Cura on custom settings. Before printing I had just changed the ABS filament for the correct color. 

Printing temp: 240 degrees Celsius

Bed temp: 110 degrees Celsius

 

Both printing cores were damaged beyong any repair. Printer didn't stop untill the heater core error appeared for core 2, this was caused by a snapped wire due to excessive amounts of ABS buildup.

Normally all goes well,. If anyone has any idea how I could prevent this from happening next time, please let me know.

2018-02-08 08.17.30.jpg

2018-02-08 08.17.24.jpg

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I don't know if the cores are destroyed but I have to admit it's a lot harder to get ABS out than PLA.  Basically you need a heat gun and pick it out slowly over the course of an hour or three.

 

The cause is when your part doesn't stick to the bed well *and* the part is much wider than it is tall when this happens.  Those are the 2 requirements.  Then what happens is the part is dragged around on the bed like a hockey puck on ice (if the part is taller than wide it is more likely to just fall over).  The nozzle keeps extruding but it is on the same spot on the part - sort of not moving.  The pressure builds up.  If you have no silicone things are even worse and the problem gets into the head a little sooner.  With the silicone it tries to stop this from happening but the pressure is high.

 

The fix is to never ever let parts slip on your bed.  For ABS this is harder to do but you can become an expert.  Watch this video.  I know it's long but it's full of valueable information.  For one thing you need that bed at 110C for ABS and you have to enclose the printer anyway for ABS to get the air up to 35C or you won't likely get good layer bonding and your parts will be weak.  Your pva looks to be much too thick - you want it so thin it's invisible and even better use ABS juice (google it - just ABS and acetone).  And finally you need to squish the hell out of the bottom layer to get it to stick well.  There are other tricks (rounded corners, brim) but squishing is critical, glass temp is critical, and a clean bed with very very thin layer of abs glue or pva is critical.  Video shows 3 ways to achieve the thin layer of glue and how exactly to get the first layer squished extra well (hint - don't use autolevel).

 

 

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Thanks for the replies! I guess that it couldn't stick well then. The parts I was printing were in fact taller than wide, but it failed after approx. 1mm height. So could definitely be the hockeypuck thing.

If you mean the silicone on the underside where the nozzles are then I had them in place. They protected it a little bit, but eventually it was no match haha. I will try and experiment a bit more with ABS. I was using it for parts that are more intended for longer use, so I figured why not print them in slightly more durable ABS. 

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I agree with gr5. I used to only make ABS parts in an enclosed UM2 with ABS juice for adhesion. This worked well most times and occasionally removed lumps of glass from the bed with the print. I was always a little concerned about overheating the enclosed UM2 and the high temp hot end limiting its life. I have now switched to nGen and found this a good alternative to ABS and much easier to print. For this I only use the thin pva system on a 90 deg bed and do not enclose the machine. It obviously depends upon your applications, but it's definitely worth trying out.

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I found that keychains and ID-card holders in my pockets survive longer in PLA than in NGEN and PET, contrary to my expectations. At least, as long as the PLA does not have to flex! In a year time PLA gets harder, stiffer and more brittle, but it does not crumble apart, also contrary to my initial expectations. So, as long as its function does not require flexing, and does not require warmer temperatures than 45°C, standard PLA might be good enough. But I don't know what it will do in 5 years time?

 

However, if flexing is required, for example in snap-fit locking mechanisms, then the tabs in PLA will break after a year when forcing them in or out, because they lost their flexibility. In that case NGEN or PET is better. I haven't printed in ABS, apart from a few test pieces, so I can't compare these to 3D-printed ABS.

 

A disadvantage is that you can not make screw threads in PLA, nor drill, because it just melts. And like almost all plastics, PLA suffers from severe creep deformation and stress cracks, if subjected to continuous loads.

 

I would suggest that you print a couple of things in various materials and keep them in your pockets all day. Keychains are a good test item. And see how they survive when in contact with hard metal keys, when getting stuck and getting bent when you move or go sitting, etc.

 

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