[SOLVED] First good, then blobs, then nothing

Hey Board...

i've build a Kossel many month ago and had it never running perfectly over more than a week

I rebuilt the printer and checked that everything is symmetric etc and was happy with the first calibration objects ... not perfect but ok.

Now i can sometimes print like it should, and the next objects fails right at the beginning. Less filament than usual coming out and some big blobs between. I reverse the filament, cut it off put it back in and it normally works again ... but only for one object and then for the next it fails again right at the beginning.

Would it sometimes happen in the print i would say it's bad filament ... but it does not. And i can manually extrude ... switch the heat off ... start a print and it works. I have no clue what is happening. Hope someone can give me a hint in the right direction.

I made photos and videos to show the problem.

Filament comes out like it should ... i think:
[youtube]VV5cu9RqTPA[/youtube]
https://www.youtube.com/watch?v=VV5cu9RqTPA

Print after this works good ... (sorry for the audio in the background ... forgot to turn off)
[youtube]6fs1adMOAVQ[/youtube]
https://youtu.be/6fs1adMOAVQ

Result:




And after this i started the same object again ... nothing changed ... and the magic happened:
[youtube]-3q65yK0EPE[/youtube]
https://youtu.be/-3q65yK0EPE

The images from a failed try before:




Edited 1 time(s). Last edit at 05/14/2016 10:38AM by state.

Videos are private so I can't see them. What sort of filament is it, pla or abs?

Sorry. Videos should be accessible now.

It's PLA 1,75mm. First layer 230°C, the others 220°C. Bed 60°C. Speed extra slow ... as you will see in the video.

As it is a Kossel i use a bowden extruder. Length of filament between extruder and hotend around 50cm / 20".

Edited 1 time(s). Last edit at 05/14/2016 07:20AM by state.

OK, so I don't have a delta and have never used a bowden, so I'm probably not the best guy to offer advice, but why let that stop me

A couple of thoughts come to mind, printing pla so slowly makes it very vulnerable to heat migrating back up into the heat break and softening the filament, dramatically increasing the friction and making it more difficult to extrude. The key thing in this case is what is happening at the extruder (the stepper motor and drive gear)? Is the motor stalling and making clicking noises, or is the gear slipping on the filament? What sort of extruder are you using? If the problem is heat creeping back up the you might find things actually work better printing a bit faster. I use 15mm/s for the first layer but typically about 60mm/s for the other layers with pla. Is that a genuine E3d hotend or a clone? If it's a clone you may find the insides would benefit from smoothing and polishing.

The second possibility from watching the video is that the extrusion is going ok but the filament just isn't sticking to the bed. The Z height seems a little high and the extrusion rather narrow. What diameter nozzle are you using? I typically put the first layer down with aournd a 0.7mm width using a 0.4 mm nozzle. Are you printing directly on the glass or is there some coating on there? I've never tried straight onto the glass, so I'm not sure how hard/easy that is. I tried blue painters tape and that can work, but it seems to go from not sticking at all, to sticking way too well with relatively small changes of settings. Currently I use glue stick on glass and that seems to be reliable and quite easy to find usable settings.

Edited 1 time(s). Last edit at 05/14/2016 08:04AM by JamesK.

The extruder is geared ... the filament gets eaten when the hotend is blocked. I looked at the filament which i pulled out after the failed print and it's not damaged ... the teeth marks of the extruder are everywhere the same. Thats a bit strange because the filament clearly does not come out evenly. Maybe the bowden gives enough flexibility for the pressure ... until the next mess is coming out of the hotend.

The nozzle is .4mm and the e3d is genuine but a little bit abused.

Yes Z should be a bit lower for a perfect first layer. I was unsure if the nozzle could be a little bit blocked by the glass plate and used a bigger distance for this tests. But bad adhesion should only and in a mess and not in filament getting stuck?

Printing directly on the glass worked mostly. Before i used painters tape and glue stick as well. Will try cleaning the plate with sugar water in the future ... read this should work good and is easy.

I will try your speed theory ... higher speed and in this case lower nozzle, it will not stick at faster speeds with this distance to the plate.

Thanks for your help!

Ok i checked the first layer width and corrected the noozle distance by changing the max z height. Width was default 200% and height i had and kept at .35mm. So thats .7mm width at the first layer. Measured this and the 3 skirt loops are exactly 2.1mm ... so on the spot

Speed changed to 15mm/s for the first layer perimeters and 20mm/s for the first layer infill.

Worked great

https://youtu.be/3k3uiNR5rSE

2nd try ... worked

Will do a 3rd try ... to be sure it was not only luck ... but i think the first layer speed was really to slow. Didn't think that to slow could be a problem, i printed that slow in the hope it avoids problems But the thing with the friction makes sense.

i will write again when i made some more tests.

Sounds good. I recommend using an absolute value for the first layer width - Slic3r's choice of using % of layer height makes it likely that if you change layer height you forget to compensate the width and end up with a value that is inappropriate. On the subject of layer heights, 0.35mm is at the thick end for your nozzle size, and it seems to get more difficult to get good results when printing near that limit. You might want to try something closer to 0.2mm for most layers, although I use 0.28mm for the first layer.

The speed issue with pla is of course the extrusion rate, so even with higher linear speeds, if you reduce layer height the extrusion rate still goes down. You might find that if you go to thinner layers the problem comes back again unless we can find the root cause. Is the fan on the extruder heatsink running at full speed at all times, and producing plenty of air flow?

The speed seems to have fixed my problem ... 3rd try is working great.

You saved me a lot of time! Thank you very much.

Should have joined this forum months ago Hope i can give back some knowledge at some time.

Thanks for the hint with the width. I will change it to a fixed value.
Regarding the height ... will try lowering this later (it s only the first layer ... the others are at .2mm) ... thanks.

Yes the hotend fan is always on. For the printed object i use currently two big 12cm fans which i activate by hand after some layers. Didn't wire them to the RAMPS while rebuilding the printer because i plan to mount a fan at the hotend for object cooling later.

Edited 1 time(s). Last edit at 05/14/2016 10:33AM by state.

You're welcome. PLA is particularly troublesome for this sort of problem, if you can get it working then most other plastics are easier on the hot-end, although they come with other issues. Personally I like abs a lot, despite the smell and the tendency for it to warp and split. Nylon is cool too, but slow to print with.

Had not much luck with ABS ... but there were so much things wrong with my old setup Have 300g left ... so next time i have a part which benefits from ABS i'll give it a try again.

Next i have to look for my x/y dimensions ... they are a little bit off ... but i don't expect problems there

If you should ever try sugar water (solve some sugar in water ... make a paper a bit wet and use the paper to clean the plate) for adhesion ... don't take too much sugar Just tried it and had real problems removing the object.