16.1.2 Objects with poor layers or surface blemishes

4.

If the object consistently appears to have skimpy lines of material being extruded (under-extrusion), or contrarily consistently appears to have excessive amounts of material being extruded (over-extrusion), this may indicate that the filament you are using has a diameter different from what the slicer expected. Measure your filament’s diameter carefully, and then if appropriate adjust the slicer’s expectation accordingly. In particular, when printing through the Polar Cloud, under the build plate screen’s “PRINT SETTINGS”, “BASIC”, adjust the “Filament Diameter”.

Variations in filament diameter (good quality filament should have pretty consistent diameter, but poorer quality filament may exhibit greater variation) can reduce the quality of your print: some areas in the print may suffer from under-extrusion while others suffer from over-extrusion. If diameter variation in a spool of filament is spoiling your print, switch to a spool of better quality filament.

5.

If objects are printing with rough surfaces, or with layers that don’t seem fully stuck together, so that the object can pull apart, the temperature of the extruder may have been too low; try increasing the temperature by 5°C and try again. In particular, if printing through the Polar Cloud, under “PRINT SETTINGS”, “BASIC”, adjust the “Temperature”.

Also check that “Layer Thickness” is set to be smaller (generally at least 20% smaller) than the “Nozzle Diameter” of the printer’s extruder: with a “Layer Thickness” that approaches the “Nozzle Diameter”, successive layers of extruded material may be getting insufficiently pressed together to fully bond, resulting in layers that can “pull apart”.

Note that an “underside” surface that is a bit “rough” due to resting on support material can be expected, especially if the support material does not break off cleanly (see item 24). Sometimes adjusting the amount or type of support can yield a smoother surface while still providing enough support; see item 24. For a surface where you need a very smooth, refined finish, however, try to orient the object so that that surface does not need support – or expect to have to do some hand-finishing of the surface after printing.

6.

The layers forming the sides of a 3D printed object normally should appear as a fused, smooth surface. Item 5 already discussed low “Temperature” (and incompatibility between “Layer Thickness” and “Nozzle Diameter”) which will lead to inadequately fused layers and hence uniform lines on all sides of an object. However, when lines or ridges appear at only some areas of sides of a print, often in a repeating pattern, there can be other factors to investigate.

Filament feeding issues, as discussed in item 7, can result in a layer being poor, hence a line or ridge at that layer. Poor quality filament can also result in layer thickness variation, appearing as lines or ridges.

Printer temperature control or mechanical problems can result in lines or ridges appearing, often in a repeating pattern. Extruder temperature fluctuations of more than about +∕-2° C are undesirable; if you notice (e.g., via the printer dashboard screen’s extruder temperature display) larger fluctuations of the extruder temperature during a print, your printer’s extruder temperature controller may need maintenance. During printing, vibrations or wobbles of the print platform, or inconsistent z height movement of the print head along the Z rod, can also result in uneven layers and hence lines or ridges in the sides of objects, typically in a repeating pattern (reflecting the underlying mechanical vibration in the printer); calibration or maintenance of your printer may be needed.

7.

If individual layers, and especially the top layer, look bad, another possibility besides too low a temperature (mentioned above in item 5), is that the filament is not feeding smoothly and hence not extruding smoothly. Make sure that the spool of filament is feeding easily and smoothly. For a Polar3D printer, for filament feeding, see Figure 2.1 of the Polar3D Printer Guide.

8.

If the extruder drive gear is not biting into the filament consistently – perhaps because it is clogged with filament flakes and needs to be cleaned, or because the filament is quite thin or the drive gear is positioned slightly too loosely – that can also result in under-extrusion. Check your printer’s instructions for cleaning or unclogging the extruder drive gear; for instance, for a Polar3D printer, see Section 6.3 of the Polar3D Printer Guide.

9.

If an object, while looking generally good at a gross level, has small “zits” or “blobs” marring its surface, take a look at where those blobs are appearing relative to where layers start or stop or “join up”. A slower “Print Speed” (under “PRINT SETTINGS”, “BASIC”) may help avoid blobs; sometimes adjusting “Retraction” (sometimes more, sometimes less) may also help avoid such blobs.

Another cause of intermittent blobs and voids in an object’s surface can be poor quality filament that has air bubbles in it, or old filament that has absorbed water;¹ when printing such filament, you’ll typically hear loud “pops” when an air bubble or water heats up in the extruder, and get resulting voids or blobs in the extruded material. Better quality, fresh filament should result in a better surface.

10.

In addition to filament diameter variations (item 4) or filament quality or age (item 9) or extruder drive gear clog (item 8) or filament not feeding smoothly (item 7), other possible causes of intermittently thin or “skimpy” sections in extrusion lines include attempting to print with settings incompatible with your printer extruder’s actual “Nozzle Diameter”: a very, very low “Layer Thickness” may have the extruder attempting to extrude with so little room above the prior layer that the plastic can’t consistently exit the extruder; or an “Extrusion Width” significantly less than the “Nozzle Diameter” can leave the extruder dribbling, rather than pushing, melted plastic.

11.

Attempting to print an object feature that is smaller than the extruder “Nozzle Diameter” is unlikely to be very successful. As discussed in item 10, the “Extrusion Width” should normally be set to be at least the “Nozzle Diameter”. When possible, consider re-designing the object to increase the size of the feature so that it can be more successfully printed. Or for a printer that supports replacing the extruder nozzle with one of a different extrusion diameter, install a smaller diameter extrusion nozzle on your printer; then you may decrease the “Extrusion Width”.

12.

Attempting to print sections of an object that are only a few times wider than the “Extrusion Width” can be challenging: sometimes such a wall section may end up with a gap or hole. Sometimes adjusting the “Extrusion Width” to evenly divide the width of that section can aid in successfully printing it: for instance, to print a section that is only 1.0 mm wide, instead of using an “Extrusion Width” of 0.4 mm, try using an “Extrusion Width” of 0.5 mm.

13.

If surfaces have blemishes where the interior print material shows through or penetrates (telegraphing), the exterior shell of material may be too thin: modify the print to have a thicker exterior (use more shells). In particular, if printing through the Polar Cloud, under “PRINT SETTINGS”, “ADVANCED”, “Quality”, adjust as relevant the “Wall Thickness”, “Bottom Layer Thickness”, and/or “Top Layer Count”. You may also want to slightly reduce “Infill Overlap” (under “PRINT SETTINGS”, “ADVANCED”, “Fill”).

14.

If the upper surface in particular has visible holes, or sags into the interior of the object, (or this may appear as “bumps” where the sagging top bulges over infill lines – commonly referred to as “pillowing”), and if you have already tried increasing the number of shells as discussed in item 13, then you may need to increase the amount of infill; see especially “Infill Amount” (under “PRINT SETTINGS”, “ADVANCED”, “Fill”). A slightly lower “Temperature” or slightly slower “Print Speed”, or even more importantly additional cooling (see the settings under “Cool”), may also help.

15.

If your printed object suffers from gaps or holes between layers, (especially at corners of the object, or when shell/perimeter diameter is changing from larger to smaller or vice-versa), then layers may not be having enough overlap or support from one layer to the next. Adding more shells to the print can provide more overlap of the layers at the exterior of the object, while increasing the amount of infill can provide more support via infill of the exterior layers; under “PRINT SETTINGS”, “ADVANCED”, “Quality”, consider increasing in particular “Wall Thickness”, as well as “Top Layer Count” (if transitions to or from flat surfaces seem to be trouble spots); under “PRINT SETTINGS”, “ADVANCED”, “Fill”, consider increasing “Infill Amount” and possibly “Infill Overlap”.

16.

If corners are messy or blurry or (unintentionally) rounded rather than sharp, or if there are ripple patterns (corner ringing) visible on vertical surfaces near direction changes (corners), the print speed may need to be slowed down. To slow down the entire print, if printing through the Polar Cloud, under “PRINT SETTINGS”, “BASIC”, adjust “Print Speed”.

Mechanical issues with the printer causing vibrations in the printer itself (the print platform, or extruder position) can also result in wavy or ripple patterns visible on object surfaces, in such cases not so much limited to object corners but rather pervasive throughout the object; check that you have no loose screws or brackets permitting undue vibration of printer parts.

17.

If you see a jog in the extruded material, or a slight bend in what should be a straight line, or a bit of a blob of material right where an intended straight line of output material crosses the exact center of the build plate of a Polar3D printer, check the calibration of the Polar3D printer (see Section 6.5 of the Polar3D Printer Guide) and try to reposition your object so that any visually “important” straight lines are not positioned exactly across the center of the build plate; see Section 15.1.3.