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mrjohnk

Retraction and Blobs

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I've been having some issues with blobs and retraction. It appears that blobs are forming before a jump. The nozzle is still for a split second, blob forms, then nozzle moves. Slicing with Cura 13.07 on Win7.

In addition, prints with high frequency of jump requirements (and retracting each time) are not completing as they end up chewing a spot in the filament eventually, even though it will print for over an hour before chewing into the filament. I have the standard delrin rub-block extruder, not the upgraded one with the roller bearing.

Added a horseshoe spacer and zip to the bowden tube connector on the extruder drive to isolate movement here, but still getting blobs.

Normal prints without the high-frequency retractions are just fine though.

Retraction is set to 45 mm/s @ 4.5mm on jumps more than 2mm. ABS printing at 255 degrees.

Picture linked below shows both blobs and the eventual failure of the print due to lack of extrusion.

Thoughts on what I can do to help?

http://www.flickr.com/photos/8465641@N07/8578127085/in/photostream/

 

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What is your print speed and what is your travel speed? If they are far enough apart (say 50mm/sec and 250mm/sec) then maybe you can skip the retraction altogether? And suffer an occasional string? Also try maybe lowering the temp? Lowering the temp should increase viscosity so that when you "stop" extruding it leaks less (toothpaste is easier to control than honey).

 

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First a couple of extra questions....What is your layer height, nozzle size and wall thickness settings? And do you still have a stock 0.4mm nozzle?

Also, do you have Cura set to hop on moves - changing z-height?

One thing that might help is to speed up your retractions - to do that you will need the latest version of Marlin that fixes retraction speed. Currently retractions happen at half the speed you ask for, most of the time. To get that fix you'll need to build your own Marlin at the moment, though, from the source on github, because the versions even in the latest Cura don't include it.

That might help reduce the blobbing a bit - but as for the problems with eventual failure ... I suspect that's related to over extrusion. Printing slower may help, but I'll know more when you tell me the various sizes I mentioned above.

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Currently, I have a stock v2 hot-end/nozzle. I also I'm running a custom compiled version of Marlin. I had downloaded the source a couple of months ago when I needed to setup PID control on my heated bed. Other than the bed settings, it is a default image from the source code. If only the newest version fixes the retraction issue, I can download and compile a new version. The current version states "THIS IS RELEASE CANDIDATE 2 FOR MARLIN 1.0.0".

I had been running retraction at 70 mm/s a couple of days ago, but was still having the blobbing issue, then changed it to 45 mm/s with no change perhaps this version of Marlin still has the limits.

As you can see below, I am not using "hop on move", but I can give that a try.

@gr5, I can try a lower temperature and I agree that lower may be good if I can get away with it. I ended up at this temperature originally to offset layer adhesion issues where the model would split horizontally due to poor layer adhesion.

Thanks for the help.

John

=========== Full Cura Profile Below ========

[profile]

layer_height = 0.2

nozzle_size = 0.4

wall_thickness = .4

solid_layer_thickness = 0.4

fill_density = 20

skirt_line_count = 6

skirt_gap = 0

print_speed = 95

print_temperature = 255

support = Everywhere

enable_raft = False

filament_diameter = 2.97

filament_density = .85

machine_center_x = 100

machine_center_y = 100

retraction_min_travel = 2

retraction_speed = 45

retraction_amount = 4.5

retraction_extra = 0

travel_speed = 150

max_z_speed = 3.0

bottom_layer_speed = 40

cool_min_layer_time = 15

fan_enabled = True

bottom_thickness = 0

enable_skin = False

model_scale = 1.0

model_rotate_base = 0

flip_x = False

flip_y = False

flip_z = False

swap_xz = False

swap_yz = False

extra_base_wall_thickness = 0.0

cool_min_feedrate = 20

fan_layer = 1

fan_speed = 17

fan_speed_max = 75

raft_margin = 5

raft_base_material_amount = 100

raft_interface_material_amount = 100

support_rate = 25

support_distance = 0.5

infill_type = Line

solid_top = True

fill_overlap = 12

bridge_speed = 100

sequence = Loops > Infill > Perimeter

force_first_layer_sequence = False

joris = False

retract_on_jumps_only = True

enable_dwindle = False

dwindle_pent_up_volume = 0.4

dwindle_slowdown_volume = 5.0

retraction_enable = True

plugin_config =

hop_on_move = False

model_matrix = 1.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,1.0

object_sink = 0.0

 

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Grrr... the forum just ate my post... let's try again...

Firstly, get the v3 bolt if you don't have it, and the spring-loaded extruder upgrade (and the v2 hot end, come to that). They make a huge difference to the reliability of the printer - especially with retractions. My printer is a totally different machine with those added. I almost never have blockages and grinding, except when I'm deliberately abusing it to find out its limits.

I think that hop on move will make it worse, because it will be pausing even longer, so I wouldn't worry with that.

Regarding retraction.... yes, try the latest firmware from the Ultimaker/Marlin fork. See my post here, about the retraction problems and fix:

http://umforum.ultimaker.com/index.php?/topic/1734-marlin-bug-the-myth-of-retraction-speed

You'll probably want to start at about 30mm/s with the new firmware. The max that will have any effect is going to be around 48mm/s - but for me, that's already more than the hardware can reliably handle.

You could try shortening your retraction distance to reduce the time spent retracting; 4.5 is generally what I use with PLA, but maybe smaller distances would still work and reduce available blobbing time?

Reducing the temp as gr5 suggested might help - or it might make it worse, it depends on your plastic's characteristics. If it reduces the flow rate too much, then it may lead to higher pressure in the head, and more likelihood of blobbing on pauses. Try it and see how it goes.

Another thing I'd be interested to have you try is simply printing at a lower speed. Try, say, 50mm/s. Printing at 95mm/s with 0.2mm layers may be leading to some pressure build up in the head if the plastic isn't getting out fast enough; that will tend to cause blobs when it does have a chance to get out. Lower speed = more likely that plastic gets out when it should, and so less pressure build up causing it to squirt out when it shouldn't.

 

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Thanks for all the great suggestions. I'll work on getting the latest fork of Marlin compiled and uploaded to the board to start with for more realistic retraction results. I do indeed already have the v3 bolt, so just need the roller kit. I may end up printing that and try to make one per Bertho's instructions.

Next print will be either smaller layers or slower speed. I may even enable the "skin" feature in Cura to still have fat layers for infill and nice skinny layers for the outter edge where the blobs are appearing. I'll just have to play with that and see how it goes.

If those adjustments don't cut it, I'll start hacking away at the temperature a little at a time to see what I can get away with.

John

 

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The skin feature might help, yeah... but the pressure build up in the 'fat infill' might still prove to be too much... and still in effect while the thinner edges are printing...

I noticed that you're also using a 0.85 packing density setting... so that's increasing your flow rate... I realize that ABS loses a little volume, but probably not 15% or more. I know that's what the Cura tooltip says... but I think I've seen people who print ABS (and I'm not one) say that a setting in the highs 90's is closer to reality.

Anyway... and interestingly, a setting of 85 increases your flow rate by 100/85.... for a 0.4mm width and 0.2mm layer height at 95mm/s, that puts your peak flow rate at (0.4 x 0.2 x 95 x 100/85) = 8.9mm^3 per second. And I think that might be on the high end of what is sustainable - and maybe too high.

I'm currently doing some testing of flow rates, as I think it's the cause of a lot of problems that people have. I will hope to publish my findings on that early next week.

In the meantime... I recommend maybe increasing the packing density a bit, and slowing down, and see if that helps.

 

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Print looking good now. Updated to latest Marlin and changed settings. Thanks for the help. Link to pic below. Also changed the order of print to Perimeter > Infill > Loops in order to drop any potential blobs in the infill instead.

http://www.flickr.com/photos/8465641@N07/8581931440/in/photostream

[profile]

layer_height = 0.2

nozzle_size = 0.4

wall_thickness = .4

solid_layer_thickness = 0.4

fill_density = 20

skirt_line_count = 6

skirt_gap = 0

print_speed = 50

print_temperature = 255

support = Everywhere

enable_raft = False

filament_diameter = 2.97

filament_density = .92

machine_center_x = 100

machine_center_y = 100

retraction_min_travel = 2

retraction_speed = 30

retraction_amount = 3

retraction_extra = 0

travel_speed = 150

max_z_speed = 3.0

bottom_layer_speed = 40

cool_min_layer_time = 15

fan_enabled = True

bottom_thickness = 0

enable_skin = True

model_scale = 1.0

model_rotate_base = 0

flip_x = False

flip_y = False

flip_z = False

swap_xz = False

swap_yz = False

extra_base_wall_thickness = 0.0

cool_min_feedrate = 20

fan_layer = 1

fan_speed = 17

fan_speed_max = 75

raft_margin = 5

raft_base_material_amount = 100

raft_interface_material_amount = 100

support_rate = 25

support_distance = 0.5

infill_type = Line

solid_top = True

fill_overlap = 12

bridge_speed = 100

sequence = Perimeter > Infill > Loops

force_first_layer_sequence = False

joris = False

retract_on_jumps_only = True

enable_dwindle = False

dwindle_pent_up_volume = 0.4

dwindle_slowdown_volume = 5.0

retraction_enable = True

plugin_config =

hop_on_move = False

model_matrix = 1.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,1.0

object_sink = 0.0

 

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I'm so jealous. I just can't get my ultimaker to print ABS properly. I'm trying your setting to see if that improves things, but I'm getting pretty depressed trying to get get *anything* to print properly.

 

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