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graeme_robinson

looking for a better way to pre-extrude PLA

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Hey, that subject rhymes - badly...

At the moment my method for beginning a print having warmed the UM up from cold is as follows (I'm using an ulticontroller):

1. use Prepare/Preheat PLA

2. do something else till pre-heat is done

3. load print gcode from card selection menu

4. begin print and observe as PLA begins to flow normally.

5. stop print and select auto-home

6. wipe aware the small amount of badly printed PLA from the print bed.

7. select the print gcode again and restart print.

From here on I can usually walk away while the printer completes its job.

On the whole this method is good but I know I could bypass steps 4 to 7 if only I could increase the amount of pre-print - that bit where the printer runs a printed line or two around the print job.

Is this just a matter of adding some more gcode to increase the amount of pre-printing before the job proper begins? I mean, I'm sure it is but can this 'pre-print' phase be extended when I generate gcode via Cura?

Mmmm - maybe this is a Cura forum question, but I wondered if there were other alternatives to achieve this so thought posting a general question a better approach, at least initially. Many thanks for your replies and comments in advance.

- Graeme

 

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or,

1. use Prepare/Preheat PLA

2. do something else till pre-heat is done

turn the wooden gear manually, until you feel the pla coming out smoothly,

remove the extruded pla under the nozzle.

(by doing that, you are sure that there is no blockage in your hot end)

3. load print gcode from card selection menu

4. begin print and observe as PLA begins to flow normally.

brim or skirt are always good, depending on your model

 

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or,

1. use Prepare/Preheat PLA

2. do something else till pre-heat is done

turn the wooden gear manually, until you feel the pla coming out smoothly,

remove the extruded pla under the nozzle.

(by doing that, you are sure that there is no blockage in your hot end)

3. load print gcode from card selection menu

4. begin print and observe as PLA begins to flow normally.

brim or skirt are always good, depending on your model

 

Thanks - good to keep in mind if I forget to compile gcode with a brim.

I'm very pleased to report my first print with Brim has nailed this problem and I'll be printing a brim on future prints to ensure there's a good even flow before the real job begins - problem solved.

 

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Brim may be overkill - it's normally set to a lot of loops, and its attached to the print. I usually find that a skirt of 3 or 4 passes is sufficient, and you don't have to worry about separating that from the print afterwards.

The other thing that will probably help is to increase the amount of priming extrusion in your starting gcode. In cura, there's a line in the starting gcode that looks something like:

G1 F200 E3 ;extrude 3mm of feed stock

I prefer to change this to:

G1 F90 E6 ;extrude 6mm of feed stock

This extrudes twice as much plastic, and at a slower pace that won't over-tax the nozzle. You could also add a delay command after that, to give yourself a chance to clean up the nozzle for easily...

G4 P2000 ; pause 2000ms

 

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Brim may be overkill - it's normally set to a lot of loops, and its attached to the print. I usually find that a skirt of 3 or 4 passes is sufficient, and you don't have to worry about separating that from the print afterwards.

<snip>

Wow, really appreciating all these insights that are incrementally levelling me up as a 3d print maker. Seriously though, just adding Brim means I can, for the first time, just start a job and walk away. Such a big improvement..

 

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Brim may be overkill - it's normally set to a lot of loops, and its attached to the print. I usually find that a skirt of 3 or 4 passes is sufficient, and you don't have to worry about separating that from the print afterwards.

The other thing that will probably help is to increase the amount of priming extrusion in your starting gcode. In cura, there's a line in the starting gcode that looks something like:

G1 F200 E3 ;extrude 3mm of feed stock

I prefer to change this to:

G1 F90 E6 ;extrude 6mm of feed stock

This extrudes twice as much plastic, and at a slower pace that won't over-tax the nozzle. You could also add a delay command after that, to give yourself a chance to clean up the nozzle for easily...

G4 P2000 ; pause 2000ms

 

That works very well for me, I was always failing adhere on first print then success on starting again, those lines cure that for my set up. Thanks.

 

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These manual steps work well for me (no Ulticontroller) with just an outline.

1) Load the print file

2) press 210 C pre-heat button under the "temp" tab

3) when temp gets close, switch to "jog" tab

4) press extrude button until good PLA is flowing and the correct color if changing colors

5) clean the nozzle and remove dross, quickly to keep pressure in hotend

6) press print button

7) grab the Z axis and crank it while making the outline to crush the extruded bead to desired thickness ex to get .2 mm thick layer with .4 mm nozzle, crush down half the bead height, 0.1 mm with 0.4 mm crush down 75%.

Scott

 

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As well as priming and wiping the nozzle manually, and using the skirt of 2-3 lines, I have my start gcode slightly modified (on my UM1). It now looks like this - added part in red:

G21 ;metric values

G90 ;absolute positioning

M107 ;start with the fan off

G28 X0 Y0 ;move X/Y to min endstops

G28 Z0 ;move Z to min endstops

G1 Z15.0 F{travel_speed} ;move the platform down 15mm

G92 E0 ;zero the extruded length

G1 F200 E2 ;extrude 2mm of feed stock

G92 E0 ;zero the extruded length again

G1 X10 Y10 Z-15 F{travel_speed} :move head to 10,10 and bed back up to 0

G1 F{travel_speed}

M117 Printing...

It makes the primed nozzle drag across the bed in transit to the skirt while not extruding. The boogers from priming are mostly wiped off. The skirt starts to print nearly perfectly and I have enough time to adjust Z manually if needed.

 

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Yes but then you wouldn't be able to print in that spot so you couldn't print full size prints unless they didn't reach that spot of the build plate. You would probably also have to cut a slot in the Z stage so that when the stage is all the way up it doesn't hit the wiper.

 

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To follow up belatedly on a n earlier comment, I don't recommend using the ulticontroller to advance the extruder on a UM1. For a start it's a pain to do, having to click several layers deep. And secondly, it advances the filament much too fast, compared to normal printing speeds. It's so much easier to just grab the gear wheel and turn it - and you can get a much better feedback as to the resistance that the extruded is encountering, and slow down before doing any damage.

 

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