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I would like to stop filament "oozing" and bridging a gap in a vertical slot. See attached image.

I assume (a very dangerous practice, I know), that this is the function of the needle valves? On this assumption I have run the Nozzle Opening routine many times. Although, this function is not particularly suitable, as it only allows a one-way setting: Increment only - decrement is not allowed.

Guessing that this setting mus be held in the head EEPROM, I have started reducing the "B:" values a step at a time. I have moved from the value stored by the calibration setup (1.5/-1.5) to 1.3/1.3. To my surprise, it still prints but the bridging is still there!

Am I moving in the wring direction? Should I be increasing the B: value. Or am I on the wrong track altogether?

Regards, Martin

1602239714-Vertical-Slots.png
4 Answers
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You aren't adjusting the correct setting. You should not adjust the nozzle B values. Those need to be set by the nozzle opening calibration and then left alone.

If your nozzles aren't closing properly, you need to open a support ticket. 

Another possibility is that your model isn't made correctly and has a zero thickness plane right there and the printer is printing that because the model is telling it there should be something there. With the way the rest of the model is built and the fact that the two slots are obscured in the manner they are, I am leaning toward this as the cause a little more than a mechanical issue.

If you see excess material at the nozzle open or close points, you need to look at why that is happening. Is it due to a malfunction of the nozzle, which a support ticket can help you with, or is it due to the material and settings? You haven't mentioned the materials you are using so it is hard to tell what may be happening. I see a lot of warping, but the material looks glossy in the photo, so I am guessing this is PETG, but it is hard to tell. The material will affect how your print turns out. 

A third option if you don't have a malfunctioning needle valve you have a problem with the filament movement or extruder so the nozzle pressure is building up too high and you get a surge of material at the start of the print, or the settings for the nozzle eject volume need to be adjusted. A support ticket will give you the best solution.

 

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Posted by: @bhudson

If your nozzles aren't closing properly, you need to open a support ticket. 

Posted by: @bhudson

Another possibility is that your model isn't made correctly and has a zero thickness plane right there and the printer is printing that because the model is telling it there should be something there. With the way the rest of the model is built and the fact that the two slots are obscured in the manner they are, I am leaning toward this as the cause a little more than a mechanical issue.

Posted by: @bhudson

You haven't mentioned the materials you are using so it is hard to tell what may be happening. I see a lot of warping, but the material looks glossy in the photo, so I am guessing this is PETG, but it is hard to tell.

1. Is there anyone dealing with Support (Covid, Furlough etc)? 

2. Excuse my ignorance but I can't find out what a "Zero Thickness Plane" is? To guess how to answer this point, if I import into Cura (v4.7.1) and preview the slicing around layer 150, I have this image: See Attached. Does that add any information?

3. No it is not PEGT. It is PLA and PolySupport in the horizontal slots.

1602329551-Cura_Preview.png
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Dho.. Now the Edit has timed out on me!

I was going to add that it is CEL PLA (Hot PInk!) and to point out that I have not had any answers to a support ticket raised 27th Sept.

@mprowe
I don't know why you haven't had an answer. Maybe follow up?

I can't tell if you have an issue with the model without seeing the model itself. If you upload that I can take a look.

A zero thickness plane is where the model is created with a plane that has zero thickness. This is usually caused by a modelling issue that leaves the definition of a surface in the model but the model doesn't contain the definition of the thickness of the surface or doesn't tie it into any other surfaces to make a solid.

Your image doesn't help because it is a different version of Cura.

That is a lot of warping with PLA. Are you printing with the door open or closed?

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Posted by: @bhudson

can't tell if you have an issue with the model without seeing the model itself. If you upload that I can take a look.

Posted by: @bhudson

That is a lot of warping with PLA. Are you printing with the door open or closed?

1. Thank you very much. .STL file attached.

2. Door is closed.

Regards,

@mprowe
While the model did not flag errors in Slic3r, AutoMaker, or 3D Builder, it did cause a surface reversed normal error using my CAD software. This means that one or more of the surfaces in the model have its inside face on the outside of the model. This is normally not a problem, but it may be causing some behavior with your specific settings that is causing the issue.

Based on looking at the seams in the model, the location of the problem, and the fact that there are normal direction errors with the model, I am inclined to think it is the model that is causing the issue. I would run a test with a CEL provided test model to see if you have similar errors.

I would also print with the door open and the right side removed for PLA, or even look into cold bed printing to reduce that warping, which may also be contributing to the issue.

What I find interesting is that the problem only occurs in certain areas of the model, pointing to model errors and not hardware errors, since those same features print fine in other areas.

If you will use the "Add Comment" button instead of the "Your Answer" field it will keep this exchange a little cleaner. This is optional though.

Posted by: @bhudson
"I would run a test with a CEL provided test model to see if you have similar errors."

Looking through the zip file of CEL Samples, I do not see an example that matches my situation. The nearest is the iPad case. But even that has gaps in the perimeters (for the iPad buttons) of many mm. Looking closely at these stops in the perimeter, I still see "oozze" but as there is no convent (or in my case inconvenient) edge to attach to, it retracts back to form a swollen termination at the end of the run.

Running a set of test prints, it seems that the minimum gap that will prevent bridging is 2mm. This also depends on the print direction: head travailing left to right is better than head printing right to left? I suspect that this is because in the first case the head is doing a "U" turn at the end of a run and in the other it is "jumping" across a gap to continue the print.

In thinking about this problem, I wonder if it is solvable? If the needle valve closes at the end of a run, there is going to be filament directly above the current (end of line) point, reaching to the nozzle. This volume has to go somewhere. I guess other printers solve this problem via "retraction"?

Lesson learnt: "A needle valve may not provide the clean cut-off that I had expected".

Posted by: @bhudson
I would also print with the door open and the right side removed for PLA,

Well this was a Revelation! All the claims of an enclosed space giving a controlled print environment - out the window! Prints a lot better (bridging excluded), thank you.

Regards, Martin
PS - Where are the editing tools and Preview, when using (as advised) the "Add Comment"?

@mprowe
The editing tools are at the bottom right corner. There isn't a preview option for comments.

From what you have reported, I suspect one of two things:
1. The filament you are using is wet and is flowing more than expected by the needle valve. PLA needs to be kept at <20% RH for the best results and absorbs most of the water it is going to in the first 24-48 hours. When wet filament is printed, its viscosity lowers and the needle valves can't always close fast enough to keep up with it. This may also happen if PLA is left at a higher temperature for a while. If your filament is at all brittle it is wet.
2. The needle valve calibration is not correct and the valves are leaking slightly while they are closing.
3. The print head isn't working properly and the valves aren't closing quickly enough or reliably.
4. The nozzle eject values aren't correct for this specific filament.

I would run the nozzle open calibration again, with known dry PLA. Go very slowly with at least 5 seconds between each click when you are clicking Not Present. Shine a light on the nozzle to see the very first indication of any ooze and that that point click Present. If the filament shows up as a sudden surge, reduce the B value by 0.05 on the affected nozzle(s). Then test. See if the problem persists.

If it does, enter Advanced Mode and use the command M999 in the gCode window to get the bDelta value. If it value is over 0.100 there may be a problem with the valve actuators. If you report the value you find I may be able to assist further.

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