Bottom Layer Compression (over extrusion) - Can't get rid of it I've been trying to find a solution to a problem I've been having recently whereby the bottom layers of my print (1.2&nbsp;mm; 12 layers) are either being compressed. over extruded or both. The problem results in the nozzle being dragged through previously extruded filament leaving deep groove marks and the bottom layers being risen/wavy, thus causing (I believe) the print layers to expand horizontally outwards 

Settings are:


Anycubic Chiron 
0.1&nbsp;mm layer height
200&nbsp;&deg;C hotends temperature
55&nbsp;&deg;C bed temperature
40&nbsp;mm/s print speed
eSun black 1.75&nbsp;mm PLA
Cura 4.4.1


It's less noticeable on less intrinsic prints but for my latest project, its becoming a real issue. The problem is that for the square holes for the buttons (of which there are a lot), the bottom layers are extruding (essentially elephants foot-ing) which is impacting the tolerances of the build (holes should be 13&nbsp;mm to accept 12.5&nbsp;mm square buttons but are coming out at ~12.7&nbsp;mm only on the bottom layer, I've measured the walls of the square holes and they're coming out perfectly).

I've tried almost everything I can think of/find on Google: 


Levelling the bed (multiple times)
Tried print temps from 190&nbsp;&deg;C to 210&nbsp;&deg;C (even printed a temp tower which confirmed printing at ~200&nbsp;&deg;C is correct for my filament (eSun black PLA)
Calibrated the extruder
Calibrated the Z-axis 
Set different horizontal expansion settings in Cura
Reduced entire print flow rates (have tried 90&nbsp;%, 85&nbsp;% and 80&nbsp;%); this somewhat worked but produced problems elsewhere in the print due to lack of material (skin overlap etc.)
Used the 'modify settings for overlap' mesh setting to reduce infill flow &amp; inner wall flow to 45&nbsp;% and 55&nbsp;% respectively for the bottom layers (up to 1.2&nbsp;mm). 


The last point in that list is where I've had the most success but it does leave a slight indentation around the outer wall until the full flow rate kicks in (i.e. >1.2&nbsp;mm) and I'm thinking there may be other things at play that are causing the issue and I shouldn't have to do this reduce bottom layer flow so much if at all.

Has anyone seen this before?
The first thing that comes to mind is that, even though you have levelled the bed, the print nozzle may be too close causing too much "squish" on the first layer. Squish isn't bad as it promotes adhesion, but in your case, as you are looking for finer tolerances on the holes, it may be a problem. I use a feeler gauge and aim for 0.15&nbsp;mm gap when printing at 0.2&nbsp;mm layer height.

Next thing to consider is ensuring you have calibrated your flow rate/extrusion multiplier. See here for detailed procedure

Assuming flow rate is calibrated I can think of some settings in Cura that could affect your print.


Initial Layer Flow
Flow Rate Compensation Factor
Combing Mode / Avoid Printed Parts


Initial Layer Flow enable the use of a higher/lower flow rate in you first layer. Typically I set this to a value larger that my flow rate, 120&nbsp;%, as I want good adhesion and am less worried about the elephant's foot effect. However, you could reduce it to less than your flow rate although that may compromise adhesion unless you use a brim.

Flow Rate Compensation Factor For most circumstances this should be 100&nbsp;% which indicates that your flow rate should be used as set and not compensated for. I would check that this value has not been altered cause over-extrusion.

Lastly, there are two travel settings. Combing Mode and Avoid Printed Parts work in combination to reducing the impact of travels in the finished print. I would ensure you have combing turned on (e.g. Not in Skin) and that you have enabled Avoid Printed Parts. More details on these settings can be found here