For proper adhesion, as well as a smooth base layer, it is important that the initial layer of the object print at the correct height above the build plate: just a little “smooshed” so that it adheres. When the z height of the first layer is well-calibrated, the lines of the first layer should be slightly touching. If there are gaps in the first layer between the lines of material, then the z height is too high; if the lines of material are overlapping and aren’t forming a smooth surface (or material is getting dragged or smeared by the print nozzle), then the z height is too low.
To adjust the calibration of the Polar3D printer, connect to your printer’s local web interface, e.g., connect to your printer’s local IP address – see Section 9.6 (or Chapter 3: The Polar3D printer local web interface of the Polar3D Printer Guide). At the Polar3D printer local web interface, select “Calibration” from the left-hand navigation pane, and then follow the z calibration procedure on that screen; see Section 6.5.1: Polar3D 1.0 printer z and x calibration or Section 6.5.2: Polar3D 2.0 or 2.5 printer z and x calibration of the Polar3D Printer Guide, as appropriate.
Also, though unlikely: check that the build plate of the Polar3D printer is maintaining a consistent height from the extruder nozzle over the build plate shuttle’s range of motion (since if the height isn’t consistent, that first layer may not be getting consistent “smooshing”). Check the z height with the extruder at the middle of the build plate; then slide the build plate shuttle forward so that the extruder is at the edge of the build plate and confirm that the z height hasn’t changed. If the z height is changing from middle to edge of build plate, then see Section 6.5 in the Polar3D Printer Guide for a discussion of checking and correcting build plate shuttle alignment.