15.2.2 Objects with poor layers or surface blemishes

6.

If layers are misaligned or shifted or twisted¹ in your object, there are several possible causes.

(a)

The object came partially loose of the build plate and shifted position at some point during the print, and after that the remaining layers are shifted, printing on top of where the bottom was supposed to be (rather than where it is). For this case, improve adhesion; see Section 14.4 for some ideas. Also check your printer’s calibration to ensure that the build plate print bed is well leveled.

(b)

You are trying to print too quickly, and the stepper motors can’t keep up with the requested speed. Try reducing in particular your “Print Speed” (under “PRINT SETTINGS”, “BASIC”), and “Move Speed” and “Infill Speed” (both under “PRINT SETTINGS”, “ADVANCED”, under “Fill” or “Speed”, respectively) – and if it’s a raft that shifted, reduce the raft “Base Speed” and “Surface Speed” (under “PRINT SETTINGS”, “BASIC”, “Platform Adhesion Type”, “Raft”, “Raft Settings”). Excess speed is a fairly common cause of layer shifting, so check whether reducing the speed(s) solves the problem.

(c)

The print head bumped a previously extruded part of the object; see the discussion in item 4, and in particular consider setting (or increasing) the “Z Hop”.

(d)

Someone bumped the printer during the print, jostling the positioning of the print head (or the object itself).

(e)

There is some kind of mechanical or electrical issue with your printer. Loose belts or pulley screws can result in the print head not moving precisely. Electrical issues may mean power is not being delivered consistently to the motors to drive the print head movement consistently. False triggering of an endstop (e.g., from loose wiring) may confuse the printer about the location of the print head.

(f)

If printing with PLA on a heated print bed, the print bed temperature may be too high; the extruded PLA on the print bed may have softened and shifted. Try lowering the “Platform Temperature”; (in particular, keep it under 70° for PLA).

7.

If the object consistently appears to have skimpy (missing sections) or “foamy” (porous) 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”.

For example, if you’ve told the printer to expect a “Filament Diameter” of 3 mm but the actual filament in use is 1.75 mm (these being two standard filament diameters sold), then the extruder will think it has more melted plastic to extrude than is actually present: even if the resulting extrusion lines look “complete” (as in, not outright missing segments of extrusion), the extruded plastic tends to look “foamy” or “porous” (as the actual volume of extruded plastic was insufficient).

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.

8.

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 34). Sometimes adjusting the amount or type of support can yield a smoother surface while still providing enough support; see item 34. 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.

9.

If a tall object printed on a printer with a heated print bed displays “cracks” (or layer separation) only towards the upper part of the object, not towards the bottom, then the object may be cooling too fast higher up (farther from the heated print bed). As with general layer separation (see item 8), try increasing the extruder “Temperature” a bit (by 5° or 10°). Next, you want the “right” amount of cooling: sometimes more cooling can “freeze” the object in place, but alternatively, sometimes less cooling allows the layers to adhere better. If your printer has a “Cooling Fan”, check that it is enabled (under “PRINT SETTINGS”, “ADVANCED”, “Cool”); or for a printer without a built-in cooling fan but with an open build area (such as a Polar3D 1.0 printer), try pointing a small external fan at the build area. But if you were already using lots of cooling, perhaps reduce the speed of the cooling fan.

10.

The layers forming the sides of a 3D printed object normally should appear as a fused, smooth surface. Item 8 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 11, 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.

11.

If individual layers, and especially the top layer, look bad, another possibility besides too low a temperature (mentioned above in item 8), 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.

12.

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.

13.

If certain layers (or sections of layers) of the object are missing, you’ve suffered some temporary under-extrusion. Several possible causes have already been discussed above, including: poor quality filament with diameter variations (item 10), filament feed problems (item 11), and extruder drive gear problems (item 12). Mechanical problems with the printer, such as a bent z rod or a bearing or clip giving out, can also result in the printer’s parts not moving freely; if nothing seems outright wrong with the printer, some lubrication of the printer’s moving parts may be helpful.

14.

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;² 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.

15.

In addition to filament diameter variations (item 7) or filament quality or age (item 14) or extruder drive gear clog (item 12) or filament not feeding smoothly (item 11), 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.

16.

Attempting to print an object feature that is smaller than the extruder “Nozzle Diameter” is unlikely to be very successful. As discussed in item 15, 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”.

17.

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.

18.

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”).

19.

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 18, 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.

20.

If a flat upper surface is marred by “scratches” upon it, where the extruder “dragged” across it without a Z hop, then check the “Retraction” settings (under “PRINT SETTINGS”, “ADVANCED”); check in particular that combing is disabled (“Enable Combing” set to “Disabled”) and that you have an adequate “Z hop” set.

21.

If the bottom surface of the object has very visible lines (ridges) rather than a smooth surface, the printer extruder calibration may need to be adjusted so that the extruder is slightly nearer to the print bed (so that the initial layer will get more “smooshed” and the extrusion lines will flow together). Printing with a smaller “Initial Layer Thickness” (under “PRINT SETTINGS”, “ADVANCED”, “QUALITY”) may also be helpful in getting a smoother bottom surface – however, be aware that the smaller the “Initial Layer Thickness”, the more important precise z height calibration of the printer extruder will become.

22.

If the first layer (the bottom) of the object seems to have extruded with blobs of filament, the extruder nozzle may be too close to the build plate (check z-axis calibration of the printer) and/or the build plate print bed may not be sufficiently level so that the extruder nozzle is too close during portions of the first layer. Check that the printer’s build plate print bed is well leveled!

23.

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”.

24.

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.

25.

If a print of a highly detailed object just doesn’t look good enough, and you’ve looked through the above issues and suggestions, then you are probably already considering decreasing “Layer Thickness” and “Print Speed” (under “PRINT SETTINGS”, “BASIC”). Also consider decreasing “Exterior Wall Speed (under “PRINT SETTINGS”, “ADVANCED”, “Speed”), which specifically controls the print speed of the outermost wall (so the visible surface of the object), as that may aid in achieving a more refined surface appearance. (Also, if you’ve been trying to use up some poor quality filament, a finely detailed object is not the time to use it! The difference between quality filament with consistent, good printing qualities, vs. a more variable filament will be more apparent in a highly detailed object; use a good quality filament when you care about fine details in the printed object.)

26.

On a Polar3D printer, if you see an object problem right at the exact center of the build plate – a jog in the extruded material, or a slight bend in what should be a straight line, or a blob of excess material, or a “hole” in the object – if you see any problem right at the center of the build plate, then 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 or sections of the object are not positioned exactly across the center of the build plate; see Section 14.1.4.