<p>I'm printing a ring that's a replacement for the non-slip base of a mixing bowl. The ring is about 130mm in diameter, with a rectangular cross section, like this:</p>
<p><a href="https://i.stack.imgur.com/9cx9Y.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9cx9Y.png" alt="rubber ring" /></a></p>
<p>I'm using Cura as the slicer, and I've set the infill to 100% and <code>concentric</code>, but after slicing it looks like Cura used <code>lines</code> instead; the ring is filled with parallel straight lines:</p>
<p><a href="https://i.stack.imgur.com/LEfXF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LEfXF.png" alt="lines infill" /></a></p>
<p>Is this a problem with Cura? Is there something I can do to encourage it to use concentric infill? I don't really care what the infill pattern is, but I think <code>concentric</code> would print a lot faster since the head wouldn't have to switch directions all the time.</p>

Is this a problem with Cura?
I don't know if the good folks at Ultimaker consider this a bug or a feature, but it appears that Cura uses the
```
Lines
```
option regardless of the
Infill Pattern
setting when
Infill Density
is set to
```
100%
```
. There may well be some reason for that; for example, the fact that the
```
Lines
```
option alternates the direction of the lines from one layer to the next probably makes for stronger parts.
Is there something I can do to encourage it to use concentric infill?
Yes!
It turns out that setting
Infill Density
to anything less than
```
100%
```
gives the expected concentric infill (provided
Infill Pattern
is set to
```
Concentric
```
, of course). When I changed the setting to
```
99.99%
```
and re-sliced, I got concentric infill in the Preview panel. I haven't tried printing yet, but I have no doubt that I'll get the same thing in the actual print.
I don't really care what the infill pattern is, but I think concentric would print a lot faster
With
Infill Density
set to
```
99.99%
```
and
Infill Pattern
set to
```
Concentric
```
, the estimated time to print my part drops from 4 hours 50 minutes to 2 hours 44 minutes,
a 44% time savings compared to 100% infill
. That's probably a lot more savings than you'd get on a part that wasn't so narrow, but it's worth knowing that at least some parts can print much faster with concentric infill.