Larger prints don't complete the base layer

[redmesh 0]

I'm becoming more ambitious but the feedrate seems to be an issue for large prints. Or it may be the leveling of the platform.

The extrusion starts well, I can print small objects 2cm to 5cm tall, I'm going for a about 15cm high next. It is the large print that's the problem, the outline of the shape base is good, 215c no problem, as the fill in for the base progresses the flow drops off and the extrusion stops gradually.

The teeth marks are visible on the filament and thumb screw for feed mechanism seem good and tight.

Any thoughts?

[joergen 2]

I'm becoming more ambitious but the feedrate seems to be an issue for large prints. Or it may be the leveling of the platform.

The extrusion starts well, I can print small objects 2cm to 5cm tall, I'm going for a about 15cm high next. It is the large print that's the problem, the outline of the shape base is good, 215c no problem, as the fill in for the base progresses the flow drops off and the extrusion stops gradually.

The teeth marks are visible on the filament and thumb screw for feed mechanism seem good and tight.

My guess is unlevelled and uneven print bed. if you print a thin first layer, and sections of it are too close to 0, the plastic isn't hot enough, and the extruder motor doesn't have enough poser to overcome that pressure, and will start stripping the filament and/or stop moving the filament.

the quick way around it is using Daid's awesome cura, and set the first layer to something really thick: i.e. 0.3-0.4mm, and go slow (25mm/s), and maybe even increase the temp by 5C for the first layers.

the slow way is leveling the bed properly, and laying down the blue tape so it doesn't make any (significant) bumps.

[gael 0]

Hi!

It's the same problem I had and that led to the topic : viewtopic.php?f=7&t=902

From what I observed, when you print large areas completeley filed, the output of the filament is restricted by the short distance between the nozzle and the printed flat surface. A back-pressure grows in the heated section of the printing head that makes the filament bulge just above the heated section. The resulting friction of the filament against the inside of the bowden tube slows down the extrusion that may stall and make fail the print...

You can first reduce this back pressure by leveling perfectly the machines table. This way you'll prevent the nozzle to get too close from the support that leads to a excessive back-pressure.

Using a thinner filament (<2.9mm) also helps to push back the moment the extrusion will get stuck.

You can do something to diagnose the problem: When you see the extrusion stalling, let the machine run and manually pull the filament out. you will be able to see the section of filament that bulged a blocked the extrusion.

On this image, you can see the indentations that increase the friction in the bowden tube, the restriction in diameter from the horseshoe clamp that increase also the friction and the bulge of the filament just above the metling section that also inceases the friction on the filament.

All this causing the printing to fail...

[IRobertI 520]

A quick check to see if it's simply that your nozzle is too close to the platform is to wait until it looks like the extrusion is getting a bit thin, then manually lower the build platform by giving the z-axis screw a little twist (two or three "clicks" should be enough), if there's suddenly a rush of plastic oozing out you will know that your nozzle is too close in that area or that your machine isn't calibrated properly and is trying to deposit too much material.

If you're overextruding that can also lead to the dreaded bowden pop followed quickly by a jam caused by plastic getting in contact with the PEEK. So it's a good idea to make sure everything is nice and level and calibrated to avoid headaches later.

[gael 0]

If you're overextruding that can also lead to the dreaded bowden pop followed quickly by a jam caused by plastic getting in contact with the PEEK.

Hi Robert,

What do you mean by "plastic getting in contact with the PEEK"? It seems to me that if the bowden tube is corrrecly held in place, the molten plastic never touch the peek; even with the pressure getting up.

++

Gael

[IRobertI 520]

Yes, normally it shouldn't happen. But, if the pressure gets too high it can lead to the bowden tube slipping from the little white thingy that keeps it in place. This then creates a small space between the brass tube of the hotend and the bowden where the plastic can ooze out. Then, as it touches the PEEK it hardens up and extrusion grinds to a halt.

This is why Owen's bowden clamp is so popular as it helps keep the bowden in place.

[gael 0]

Robert,

I agree with you, the worse case is the bowden tube being pushed back and molten plastic making a plug against the Peek part.

What I stated earlier is that before to reach this point, if the pressure in the bowden tube raises too much, the extrusion will stall before the tube moves. A solution to improve that is to reduce the friction that has a role in the pressure in the extrusion head and at the same time reduce the back pressure by trimming the UM's Table.

++

Gaël

[joergen 2]

I agree with you, the worse case is the bowden tube being pushed back and molten plastic making a plug against the Peek part.

What I stated earlier is that before to reach this point, if the pressure in the bowden tube raises too much, the extrusion will stall before the tube moves. A solution to improve that is to reduce the friction that has a role in the pressure in the extrusion head and at the same time reduce the back pressure by trimming the UM's Table.

Unfortunately, I think you are wrong with your assumptions (also in your other post). One of the first things that will give is the Bowden popping up, this is the reason why Owen designed the bowden clamp on thingiverse, to keep the bowden longer in place, other and more elaborate designs do away with a friction based bowden holder, and use M7 threads.

back to your other post, the bowden isn't too small, and the transition between the bowden and the brass tube needs to be straight and easy passage. the hose shoe clamp does NOT restrict the bowden in diameter, simply because the bowden is a mechanically much stronger part, and it is actually part of the white retainer ring, that is supposed to hold the bowden.

[gael 0]

Hi Joergen,

I understand what you say.

In this case, why does the extrusion stops even if the bowden tube is correctly held against the brass tube and the bowden tube does not move at all?

(I placed marks on the original tube and when the filament got stuck, the tube remained in place.)

++

Gael

[redmesh 0]

Thanks for the quick responses and suggestions - what a great forum this is, as I recently built the ultimaker I've taken the advice as one step at a time one problem at a time and I'll try the cura thicker bed start and also align the bed more accurately.