Need help with cause of tiny holes in printed models

[Rob W]

My prints occasionally have small holes in them, usually in sloping areas (loops), and usually penetrating down into the infill (deep_holes.jpg).

The same prints sometimes also have sections of flat surfaces (solid infill) where there are holes that are only a few layers deep (shallow_holes.jpg).  This appears to only happen when the solid infill area is less than ~0.5 cm^2 and/or is at the top of a local "hill". 

I don't know if these two types of hole have the same cause, and neither one appears in the paths produced by Kisslicer.  It's definitely a printing error, not a slicing error.  It looks like it's probably an extrusion rate or temperature issue (or possibly skin thickness or infill percentage), but I haven't found a small enough test model to go through all the permutations.  I'm hoping somebody has run into similar problems and can give me some pointers on what to try first.

Printer: BfB 3D Touch (two-head model) with after-market heated bed (bed temperature 80°C).
Material: 3mm NatureWorks Silver PLA from UltiMachine

Here are the settings I used for the pictured print:

; *** Material Settings for Extruder 1 ***
;
; material_name = Copy of PLA - Ultimachine Silver - heated be
;     d
; g_code_matl = 3B204D617962652073657420736F6D65206D6174657269
;     616C2D737065636966696320472D636F64653F
; fan_Z_mm = 0
; fan_loops_percent = 100
; fan_inside_percent = 100
; fan_cool_percent = 100
; temperature_C = 190
; keep_warm_C = 126
; first_layer_C = 210
; bed_C = 68
; sec_per_C_per_C = 0
; flow_min_mm3_per_s = 0.01
; flow_max_mm3_per_s = 10
; destring_suck = 1.75
; destring_prime = 1.25
; destring_min_mm = 0
; destring_trigger_mm = 100
; destring_speed_mm_per_s = 15
; Z_lift_mm = 0
; min_layer_time_s = 0
; wipe_mm = 4
; cost_per_cm3 = 0.058
; flowrate_tweak = 0.93
; fiber_dia_mm = 2.87
; color = 0
;
; *** Style Settings ***
;
; style_name = High Res - 20% Infill
; layer_thickness_mm = 0.125
; extrusion_width_mm = 0.4
; num_loops = 3
; skin_thickness_mm = 1.25
; infill_extrusion_width = 0.5
; infill_density_denominator = 4
; stacked_layers = 4
; use_destring = 1
; use_wipe = 1
; loops_insideout = 1
; infill_st_oct_rnd = 2
; inset_surface_xy_mm = 0.075
; seam_jitter_degrees = 0
; seam_depth_scaler = 1
;
; *** Support Settings ***
;
; support_name = No Support
; support_sheathe = 0
; support_density = 0
; support_inflate_mm = 0
; support_gap_mm = 0.5
; support_angle_deg = 45
; support_z_max_mm = -1
; sheathe_z_max_mm = -1
; raft_mode = 1
; prime_pillar_mode = 0
; raft_inflate_mm = 1
;
; *** Actual Slicing Settings As Used ***
;
; layer_thickness_mm = 0.125
; extrusion_width = 0.4
; num_ISOs = 3
; wall_thickness = 1.25
; infill_style = 5
; support_style = 0
; support_angle = 44.9
; destring_min_mm = 0
; stacked_infill_layers = 4
; raft_style = 1
; extra_raft_depth = 0.4
; oversample_res_mm = 0.05
; crowning_threshold_mm = 0.0125
; loops_insideout = 1
; solid_loop_overlap_fraction = 1
; inflate_raft_mm = 1
; inflate_support_mm = 0
; model_support_gap_mm = 0.5
; infill_st_oct_rnd = 2
; support_Z_max_mm = 1e+20
; sheathe_Z_max_mm = 0
; inset_surface_xy_mm = 0.075
; seam_jitter_degrees = 0
; seam_depth_scaler = 1
; Speed vs Quality = 0.75
; Perimeter Speed = 6.00
; Solid Speed = 24.00
; Sparse Speed = 11.50

[joseph perry]

Wondering if you have an answer to this yet. I noticed the same problem on one of my prints though it was on my support structure. I'm very new to dual extrusion and almost as new to printing with PLA. Right now I'm only using PLA for support but when I did see what you are talking about, I noticed that it was just after the support changed from coarse to fine. It looked to me like the strings were too hot to bridge the larger gaps so they would adhere in blobs to the previously existing 'cross ribs' of the coarse support matrix but in between the ribs they would thin out or even sever. I thought it was because the plastic was too hot so I changed the temp from 180c down to 170 in 5 degree increments and it seemed to help a little. I don't have a cooling fan yet though so I started spraying canned air on it while it was printing and that worked even better. I'd imagine your printer has cooling fans. I wonder if they are working. Also, I wonder if you could use a lower temperature than 190c and perhaps finer infill? I'm curious to hear how it's going for you.
joe

[toranarod]

I had holes in my prints. I also have a BFB printer.  A hole or a gape in the material is caused by a lack of filament.  

I went almost nuts trying to solve this problem.   For me it was a two problem issue.  How old is your printer or how much work has it done. 

The 3D touch nozzles are .5 mm I would say by now they are much bigger than that. problem 1 is the nozzles wear just like a automotive spry gun wears out it needle and seat.

This is the first thing that contributes to the holes in the object combine this with the main problem, the filament.  If you get a piece of your plastic and cut it open length ways you will find at various intervals air pockets. Small vacuum voids as one manufacture final admitted to me when I presented him with hard evidence these voids are vacuum gaps that occur during manufacture. They are not air bubbles. 

In most extruder's theses voids are not a problem, As the plastic is heated and compressed to its finial dimensions the voids are compressed out.    

However combine the BFB extruder design and a bit of wear, and a lack of plastic at one point here and there and you get what you see in your objects.

You can not do anything about the filament  as no manufacture will admit to air bubbles in there plastic.

The solution is to replace your hot end that has longer passage that slowly reduces to 0. 5mm . Any other manufacture will do. 

Soon as I did that all gaps gone.

Let me know if this is what your gap problem is?  Good luck

[joseph perry]

My hot ends are only 3 months old E3D v5's. I guess there are more causes than we realize. Learn something new every day! I know I still need to make some cooling fans though. Good luck to you!

[Colen Casey]

I have started seeing the same thing in my prints
i'm really not sure why I just changed to a e3d v6 hotend (amazing hotend), much better than my v5
Turn the temp up on your layers
try raising your temp 10c and see how it looks
turning up the extrusion speed worked for me but the proper fix would be to turn up the heat a little so it can extrude properly