<p>I'm printing parts for a HEVO (<a href="https://www.thingiverse.com/thing:2254103" rel="nofollow noreferrer">HyperCube Evolution</a> CoreXY), using Colorfabb XT filament. After several successful prints. I'm having a lot of failed prints. They start off pretty well but after ~15 layers the filament starts to string and blob. </p>

<p>Printer details</p>

<pre><code>Model: RepRap i3 
Extruder: E3D 1.75 all metal hotend.
Nozzle: .4
Print temp: 260°C (max. recommended).
</code></pre>

<p>Steps I took to troubleshoot</p>

<ol>
<li>First I thought my nozzle was clogged. But it's not I can push the filament by hand without issues.</li>
<li>Lowered the speed to 35&nbsp;mm/s.</li>
<li>Disabled retraction / disabled part cooling.</li>
<li>increased the max temp with 10&nbsp;% to ensure the filament flow</li>
</ol>

<p>Printed parts that fail: </p>

<p><a href="https://i.stack.imgur.com/2wEjO.jpg" rel="nofollow noreferrer" title="Top view printed part"><img src="https://i.stack.imgur.com/2wEjO.jpg" alt="Top view printed part" title="Top view printed part"></a>
<em>Note: the two parts on the left are printed in one job</em></p>

<p><a href="https://i.stack.imgur.com/1jure.jpg" rel="nofollow noreferrer" title="Side view printed part"><img src="https://i.stack.imgur.com/1jure.jpg" alt="Side view printed part" title="Side view printed part"></a></p>

<p>UPDATE 26/07
Dit a few more prints with PETG to eliminate the moisture problem. Same results.</p>

<p><a href="https://i.stack.imgur.com/l6vj4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l6vj4.jpg" alt="PETG"></a></p>

<p><a href="https://i.stack.imgur.com/GL1IF.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GL1IF.jpg" alt="PETG2"></a></p>

[{'answer_id': 6390, 'author': 'Valmond', 'author_id': 8328, 'author_profile': 'https://3dprinting.stackexchange.com/users/8328', 'pm_score': 3, 'selected': False, 'text': "<p>This looks a lot like <strong>under extrusion caused by heat creep</strong>.</p>\n\n<p>Heat creep is when the nozzle temperature 'creeps' up through the filament and makes it melt (a bit) and form a blob (or just widen enough to get stuck) a centimeter or two before the nozzle.</p>\n\n<p>The characteristic is usually that everything works perfectly well for some quite fix amount of time, then there is severe under extrusion.</p>\n\n<p>Solutions:</p>\n\n<ul>\n<li>Lower the temperature (yes, as then the heat won't creep as much!)</li>\n<li>Add a fan cooling down the cooling part of the print head</li>\n</ul>\n\n<p>I have the same print head as you it seems (E3D 1.75 all metal) and I had heat creep when I changed the fan to a less noisy one (but also less effective).</p>\n"}, {'answer_id': 6393, 'author': 'Sean Houlihane', 'author_id': 4927, 'author_profile': 'https://3dprinting.stackexchange.com/users/4927', 'pm_score': 3, 'selected': False, 'text': "<p>This suggestion may not apply in your specific case (you seem to have looked closely at the problem, and it doesn't really fit the apparent time-dependence) but you might have an issue with the extrusion drive. If your hobbed drive isn't tight on the stepper motor then the 'push' might not be enough to match the force you've tested by hand. This explains one way that the extruder can be more sensitive to small performance variations than you would normally expect (heat build up somehow contributing to those variations).</p>\n"}, {'answer_id': 6408, 'author': 'Toon', 'author_id': 9303, 'author_profile': 'https://3dprinting.stackexchange.com/users/9303', 'pm_score': 2, 'selected': False, 'text': '<p>I have a possible cause for my problems. XT is sensitive to moisture (hydrolytical stability) When I extruded 20mm filament manually, the string felt a bit rough. When I looked closer very tiny bubbels where visible. I baked the filament at 60°C for 2 hours.</p>\n\n<p>The baked filament allowed me to print a perfect model. </p>\n\n<p>But after one print the filament is again affected by moisture so I need to build a dry-box and do some more tests before I come to a conclusion. </p>\n'}]
['https://3dprinting.stackexchange.com/questions/6377', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/9303/']