<p>My i3 MK3 is printing very well for solid parts of an object, but it messes up with infill.</p>

<p><a href="https://i.stack.imgur.com/dc5BL.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dc5BL.jpg" alt="Infill rough"></a></p>

<p>As you can see in the image, the infill is broken into pieces and bends to that the surface becomes rough and the nozzle touches it next time it moves there, which probably does not make things better.</p>

<p>I've read the <a href="https://www.prusaprinters.org/7-problems-affecting-quality-of-3d-prints" rel="nofollow noreferrer">Prusa problem page</a>, where they suggest three solutions:</p>

<ul>
<li>change infill type</li>
<li>flexible filament (I'm using PETG, so this does not apply)</li>
<li>lower printing speed</li>
</ul>

<p>I'm printing with 20% infill and I believe that this worked before at the same speed, so I'm tempted to say that both remaining options are options, but it should work without them.</p>

<p>It also seems to me as if the infill is thinner that ordinary walls. Is the extrusion speed lower in case of infill? Is there a way of changing the extrusion speed for infill?</p>

<p>Side note: my printer always tells me to upgrade to the latest firmware 3.5.1. Since I have just received the printer back from a warranty repair after the last firmware upgrade, I don't want to upgrade the firmware. Could the issue be related to firmware?</p>

<p>Infos requested from comments:</p>

<p>I'm basically using the Slic3r default settings for PETG. The only thing I adjusted is the temperature, since I'm using HDGlass PETG and there was a recommended temperature written on the spool. Relevant settings seem to be</p>

<ul>
<li>Filament settings

<ul>
<li>fan speed min 30 % max 50 %</li>
<li>bridges fan speed 50 %</li>
<li>enable fan below 20 s</li>
<li>slow down below 20 s</li>
<li>min print speed 15 mm/s</li>
</ul></li>
<li>Speed settings

<ul>
<li>Perimenters 45 mm/s</li>
<li>Small perimeters 25 mm/s</li>
<li>External perimeters 35 mm/s</li>
<li>Infill 200 mm/s</li>
<li>Solid infill 200 mm/s </li>
<li>Top solid infill 50 mm/s</li>
</ul></li>
</ul>

[{'answer_id': 8233, 'author': '0scar', 'author_id': 5740, 'author_profile': 'https://3dprinting.stackexchange.com/users/5740', 'pm_score': 3, 'selected': True, 'text': '<p>From your comments can be read that you print infill at 200&nbsp;mm/s. </p>\n\n<p>Know that 200&nbsp;mm/s is ridiculously fast (like high travelling speed), close to the limits of printing on certain machines (<a href="/a/8108">for an AtMega</a>)! It is hard for the filament to keep up at this speed. A value of 60&nbsp;mm/s would be a good value to start experimenting. Your infill is not rough, it just failed printing. I have printed kilometers of PETG, normal print speeds for my PETG are recommended at 30-50&nbsp;mm/s by my manufacturer; I get good results at 50-60&nbsp;mm/s. On my Ultimaker 3, 70&nbsp;mm/s is also feasible.</p>\n\n<hr>\n\n<p><em>Note that the filament you use seems to have rather <a href="https://www.formfutura.com/shop/product/hdglass-clear-238" rel="nofollow noreferrer">low printing temperatures</a> (195-225&nbsp;&deg;C) as opposed to the PETG filament (co-polymer) I\'m used to. The manufacturer does not specify advised print speeds (other than "high", but what defines "high"?), but <a href="https://mevade.wordpress.com/2015/08/22/1-75mm-hdglass/" rel="nofollow noreferrer">this user posted</a> some of his print settings for this material. The overall speed of 60&nbsp;mm/s seems to support lower than 200&nbsp;mm/s print speeds.</em></p>\n'}, {'answer_id': 8237, 'author': 'Jeremy Bunn', 'author_id': 14510, 'author_profile': 'https://3dprinting.stackexchange.com/users/14510', 'pm_score': 1, 'selected': False, 'text': '<p>I have dealt with this on infill as well on multiple MK3s.</p>\n\n<p>However, it was not the speed itself, but the hot end having difficulty extruding enough to keep up with the infill.  </p>\n\n<p>Some things to try:</p>\n\n<ul>\n<li>Raise hot end temperature 5 degrees (melt filament faster)</li>\n<li>Lower infill speed, it will not affect your overall print time very much (surprisingly)</li>\n<li>A combination of the two above.</li>\n</ul>\n\n<p>Good luck!</p>\n'}]
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