Blobs and Oozing

This article's failure is a result of excess material oozing out of your nozzle when no material should be extruded. 

Increase retraction settings
Retraction occurs when your printer head is travelling as to reduce any excess material coming out of the nozzle. Essentially you will need higher retraction settings the further your extruder is from your hotend.

This means that when you use a Bowden setup you will need much higher retraction settings than when you use a direct extruder. You will also need higher retraction settings if there is a small gap between your direct extruder and hotend versus something like the Hemera, which has nearly eliminated that gap entirely. The smaller the gap between your extruder and hotend, the less retraction you will need, and the easier it will be to avoid blobs and strings on your print.

It is also very important to understand the material you are using. I can print something in PLA without any blobs or stringiness by just honing in my settings, but it is just about impossible to avoid some strings when printing in PETG. If you plan on printing in PETG, you will likely have to use a razor blade or a heat gun to remove the minor amount of stringing that will be inevitable.

Increase travel speeds
Since these blobs and strings will only occur when the hotend is not actively printing, you can help reduce the amount of time the nozzle is travelling by increasing the travel speeds. So long as your stepper motors and frame can handle the increased acceleration and speeds, you can bump your travel speed way up.

I currently have my travel speeds set to 200mm/s with my accelerations around 2,500mm/s/s on my CoreXY machines. You can try these numbers out on your machine, but if you experience a lot of machine rattling or hear any stepper motor skips, you will want to reduce these speeds. The highest speeds you can go without experiencing issues will drastically help reduce these strings and blobs. Since you aren’t printing while the hotend is travelling, you should not experience any reduced quality in your prints with these high travel speeds.

The photo above shows two retraction test prints, the only difference between the two is an increased travel speed for the print on the right.

Play around with Coasting
Coasting replaces the last part of an extrusion path with a travel path. Replacing the last section of a print with a travel path will cause any oozed material to be used to print your part to reduce stringing. As you can see in my “Missing Layers and Holes in Prints” article, if you have coasting on when you do not have issues with stringing, it can result in holes on the side of your print.

That said, for the majority of inexpensive Bowden printers, you will likely see an improvement in print quality when you utilize Coasting. This is particularly true when printing in something like PETG which is more likely to cause stringing issues than PLA.

Coasting is still in the “Experimental” section on Cura, though other slicers have made it a standard setting. I expect it to move out of that “Experimental” section in coming updates to Cura.

Change Z Seam Alignment
Changing your Z Seam Alignment will help more so with blobs than stringiness. It will be essentially impossible to avoid a minor seam on your print no matter what you do, but you can mitigate its effects by changing the Z Seam Alignment.

There is a setting for Z Seam Alignment where you can choose “Random”. I do notknow of a time when you would want to use a random Z Seam Alignment, but if you do choose it, you will likely see ugly little blobs all over your print. The best option for Z Seam Alignment seems to be “Sharpest Corner”, which hides these artifacts as best as your slicer can, though it will be near impossible to remove them entirely on a print that has no corners, such as a cylinder.

The photo above shows a cylinder with the Z Seam Alignment set to “Random” on the right, and the one on the left has it set to “Sharpest Corner”.

Decrease Minimum Layer Time
Some slicers have the “Minimum Layer Time” set too high for the majority of materials. This minimum layer time will cause your hotend to pause after completing a layer that finished faster than the value you have set. For instance, if I set my minimum layer time to 10 seconds, and a layer finishes in 5 seconds, your print head will pause in place for 5 seconds before starting the next layer.

This pause will inevitably lead to oozing as your hotend sits idle, and will cause both blobs and strings on your print. For the majority of materials a 3 second minimum layer time is enough, and so long as you aren’t seeing curling of layers, you can keep yours set to 3 seconds as well.
Issues with power loss recovery

Some printers utilize power loss recovery by saving its progress after each layer so that you can resume where you left off in a power outage. The issue with this is that some printers take a second or so to save the progress before starting the next layer.

My FLSUN SuperRacer delta printer had this exact issue. After each layer it would pause briefly before starting the next layer, causing blobs to appear throughout the print. I had thought that I had my “Minimum Layer Time” set too high, but it ends up it was related to the power loss recovery feature on the printer. After turning offpower loss recovery, the printer no longer paused after each layer and printed without any blobs.

This unfortunately means you would no longer have the capability to start a print after a power outage, but it just seems that some printer manufacturers have not implemented this feature properly on their machines.

Potential over extrusion
It is also possible that you will get some blobs on your print if you are over extruding. You can imagine if more material comes out of your nozzle than is supposed to, it can lead to not only an ugly print, but one with artifacts where the excess material squeezed out. 

Dry or Swap Materials
As with many issues covered in this book, poorly made filament or material that has absorbed moisture can also lead to increased blobs and strings on your print. 

Summary of Fixes and Precautions
• Increase your retraction settings.
• Increase your travel speeds.
• Turn on coasting for Bowden printers.
• Try “Sharpest Corner” for your Z Seam Alignment to reduce the visibility of the seam.
• Decrease your Minimum Layer Time so that your printer isn’t paused in place when it isn’t required.
• Check to see if your printer is pausing after each layer due to its power loss recovery function.
• Check to see if you are over extruding.
• Dry or swap to new filament.