Extrusion width and part size issues

I'm having major problems with parts from my printer. Everything is calibrated correctly and objects come out the correct size, however internal holes are smaller than they should be. The extrusion width calibration test pieces do not fit together.

After following various guides on how to fix this, I reduced the extrusion multiplier in Slic3r to 0.84. Now the calibration pieces do fit together perfectly. I also printed the 0.5mm single wall test piece and it does indeed come out as having exactly 0.5mm walls. All sounds good right? Well no, now every object is too small! In addition, the top surfaces are full of gaps and look terrible.

I don't know what else I can change in both the printer and Slic3r settings to get correctly sized objects with a solid top layer, and correct internal hole dimensions.

I am using a 0.5mm nozzle with 3mm PLA.

There is nothing to do with circles but to oversize them. If you calibrate your printer for right size circles, your cubes will come out too big. Get your cubes to perfect size and then find the right oversize for your circles.

For me a 3 mm circle needs to be 3.2 to come out exact at 3 and my cubes are exact to the tee.

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ggherbaz
There is nothing to do with circles but to oversize them. If you calibrate your printer for right size circles, your cubes will come out too big. Get your cubes to perfect size and then find the right oversize for your circles.

For me a 3 mm circle needs to be 3.2 to come out exact at 3 and my cubes are exact to the tee.

It's actually internal squares which are too small.

In that case, don't reduce your extrusion multiplier but your extrusion width.

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ggherbaz
In that case, don't reduce your extrusion multiplier but your extrusion width.

My extrusion width is already equal to nozzle size, so I can't reduce any further

well, I don't know if your slicer have the option or not, but I will switch from outside-in to inside-out on the printing and see if that gives you the right measuring inside? if not, I would put back the multiplier to 1 and re-calibrate all axis (specially the extruder)

Ok thanks, I'll try the inside out option.

If you are using the newest slic3r version 1.26, you'll find an option "XY Size Compensation" in "Print Settings" --> "Advanced" as a better way than changing the extrusion amount as it avoids small holes in the surfaces.

Ok so I tried the outside in option and it did indeed fix the problem, but it also created new ones, including generally reducing print quality.

The XY size compensation option sounds promising, I'll get the new version and try it out!

Thanks to both for your help.