Blobs on 3D print..

As suggested in the thread about modelling a cotton reel...

Here's a new thread about problems with 3D prints... and hopefully how to solve them!

My problem is blobs on the print..

I suspect that they occur when the extruder starts and stops..

Any other ideas..?? and how to stop them!!

I'm using a Creality Ender 3 V2

This is what they look like...

Thanks!!

Alan

Looks like your retract setting is too low, so the filament oozes as the head is moving from one move to another.

Usually a setting in the slicer I think

Dave

I'm using CURA as the slicer... retract is set to 5mm

I'll try something greater later

Alan

Alan, they really are quite impressive!

Some general info on 3D print problems HERE

I'm guessing from the amount of blobs, you are running a very low layer height? If so dropping the temp 10 - 15° could help.

Good luck.

Jim

Chep on youtube has recently posted a video about this problem. I will try posting a link.

https://www.youtube.com/watch?v=c_llLYxbJ4A

It's well worth a watch.

Thanks for the suggestions!

I'll try lowering the print temperature (currently 200 C)

And will look at the suggested links and YouTube

Alan

with that many blobs and seemingly random, i do not think it is a retraction poroblem.

Are the blobs solid or hollow?

What material are you using?

How old is it?

One thing I would definitely do is reduce the teperature and see if it improives things.

It could be moisture in the filament that is expanding in the extruder pushing out more filament than is needed.

hence the randomness of the bubbles.

Edited By Howi on 24/04/2022 10:05:56

Looks like you are running waaaayyy too hot and too slow imo!

Turn nozzle temp down. And print speed up.

Could also be a nozzle size/layer height ratio problem?

Edited By Hollowpoint on 24/04/2022 10:10:04

I'm currently printing the cotton reel again... Its still blobbing... but not so much..

I've lowered the nozzle temperature to 180 (from 200..)

I've not changed the retract.. its still at 5mm

The material is PLA... only opened the reel a few days ago..

I've looked at the CHEP youtube that Lee recommended.. but it seems more to do with the new version of CURA.

I'm using CURA 4.13.1 (CURA 5.1 beta won't run on my linux system..)

Thanks for all the suggestions!!

Alan

Edited By Alan on 24/04/2022 17:53:49

So...

The 2nd print was just as blobby as the first...

BUT... the 3rd print was smooth... !!

This was printed direct from the micro SD card in the printer.

The blobby prints were printed by using OctoPi..

Doing some Googling... it seems that there is a known problem with data transfer on prints that use a curved surface...

The slicer chops it up into lots of small straight lines, and this is what OctoPi tries to send to the printer.

There appears to be a plug-in to stop this.. so I'll try that next.

Alan

Glad you got it sorted!

Jim

I couldn't get on with Octopi until I ran the pi from the Ender power supply. The stepper motors caused too much noise.

So now I run the 20Vfrom my ender supply into a voltage converter to drive the pi. No comms problems since...

Good news and an interesting thing to file away for next time I have a blobby print

Dave

So...

I've now printed the cotton reel twice more..

Using the arcwelder plugin in both Octoprint and in Cura...

This one is using the plugin in Octoprint...

Still blobby... and there are some on the other side...but nowhere near as bad...

And this one with the plugin in CURA...

Still blobby... and with none on the other side... but much better...

I think that these simple tests show that using the ArcWelder plugin in CURA gives the best results... still not perfect though... I can see my collection of cotton reels growing as I try to get this working properly!!

Alan

While I'm here...

A short intro to what arcwelder does... (as I understand it..)

Normally a slicer cuts arcs and curves into short straight lines...

If there are lots of arcs or curves (as on a circle...) there will be a lot of short straight lines.

This means a lot of gcode, which can cause a data bottleneck between Octoprint and the printer.

Where the printer waits for some more gcode, it leaves a blob.

With the slicer using arcwelder, the arcs and curves are changed from short straight lines to arcs and curves, which results in a lot less gcode to send to the printer... sometimes up to 75% less..!!

This means that the data bottleneck is a lot less likely to occur, meaning a blobless print.

Obviously printing straight from the SD card doesn't have the same bottleneck problem, and so prints have no blobs...

I'm not sure if the problem with the bottleneck will be improved with a faster RaspberryPi running Octoprint...

I'm currently using a model 3b... still waiting for a model 4 to come into stock..!!

Alan

I've never used octopi or even know much about it but it seems like the solution would be to print from the SD card remotely using the octopi as nothing more than a controller.

I would use another slicer or maybe a faster Pi.

I use Prusaslicer and print at 100mm/sec from Octoprint with no problems.

Bruce

Octopi will let you download the entire file to its internal memory before printing. That eliminates the network bottleneck and the necessity of saving to an SD card and plugging it in.

Thanks Ron...

Octoprint is getting the entire file into its memory...

The bottleneck seems to be between Octoprint and the 3D printer.. So hopefully not a network bottleneck..

There's very little network traffic... only a small network!

This is why printing from the SD card is fault free..

Alan

I like the thinking, but it's unlikely the serial interface is a bottleneck. My version of the Cotton Reel gcode is 2.4 million characters in 75102 lines, one gcode instruction per line. (I think Alan is right to suggest there's a lot of gcode because the cotton-reel is so curvy.)

Sounds a lot but 3D printers usually connect with the USB serial link running at 115200 bits per second, or roughly 10000 characters per second. Therefore I'd expect the cotton reel gcode to transfer in 4 minutes, a bit over 300 instructions per second.

As the cotton reel takes 90 minutes to print, my printer obeys a little under 14 gcode instructions per second, which means the serial interface is 20x faster than the printer. And this is the worst case, assuming that the printer executes one gcode instruction at a time as each is received via the USB cable. More usual for programmers to buffer downloads by reading many lines at a time and reading ahead means the printer never waits for gcode to arrive. The average size of a cotton reel gcode instruction is 32 characters, so a tiny 4096 byte buffer would read 128 gcode instructions per gulp. Actually, the buffer could be big enough to read all 75102 instructions before the bed and extruder have finished heating up.

That said, could be a bug or configuration problem. I can't get my Ender3 Pro to print with USB at all. In theory, Cura is able to send gcode direct to the printer from Windows or Linux. Nope. Monitoring the serial interface shows the printer responds but chokes on gcode, whilst Cura doesn't recognise the printer for bed heating etc. pronterface not working either. Something ain't right with my USB, so I print with the memory card instead. The USB problem is on my ever growing 'To Do' list...

Dave