As long as I print large parts (where every slice is, e.g. at least 5mm x 5mm) my Prusa i3 produces what looks to be very accurate models.

When I try to print small parts, there's a lot of jitter and inaccuracy in the printed model.

For example, this was sliced using Cura with 30mm/sec speed and 1mm retraction (30mm/sec retraction speed as well):


The widest square tower (rightmost at the top image) is 3mm wide, and isn't very accurate, but the narrower towers are even less accurate.
On the bottom part, it's quite evident that as the cones become narrower, they're less accurate. The more complex towers on the left hand
side of the bottom image are almost accurate, and are wider.

I tried changing the retraction to 4.5mm, which was recommended in Cura (I got the 1mm value from the kit seller). This removed a few of
the small leftover plastic threads, but didn't make a substantial difference to print accuracy:


One final attempt - I lowered the print speed of the shell (not the infill) to 10mm/sec. The result was better:

Still, this is not very accurate on the narrower parts.

BTW, I was using slic3r before, but results are roughly the same.

Any recommendation on what could cause this?

Thanks.

Needs more cooling. The slower speeds are allowing more time for the prior layers to cool. Slic3r's cooling might help: [github.com]