3DPrinting

So let’s recap the way a FDM printer works.

In a sense it’s like a hot glue gun.

Step 1 is to heat the filament. That makes it molten and fluidic.

Step 2 is to exert pressure with new filament (like pushing unmelted hot glue to push out the melted glue) into the melt zone. This pressure squeezes the melted plastic out the nozzle.

Too much pressure and it’s too wide. Too little and it doesn’t make a line wide enough.

A lot of times tuning the first layer is about getting these figures just right and the distance of the nozzle where it’s expected.

So why the purge line?

Because it takes a little time to get consistent push for consistent lines with the newly melted plastic. Just like pressing the trigger of a brand new hot glue gun with a brand new glue stick doesn’t give you glue right away. It has to be “primed”.

So the purge line does it. It’s a line that you draw so that the filament has time to be consistent (since new filament, different temps, different pressures and even retractions will change how much is available to come out as soon as the printer “pushes” on the filament)

Purge lines can be implemented in a slicer (see: skirts), your printer's firmware, or macro if your running klipper. Slicer based purge lines are optional in Slic3r and its derivatives (PrusaSlicer, etc) as well as Cura.

Why are they there? When your hot end sits hot, filament in the melt zone will slowly ooze out. This happens to me while my printer waits for the bed to heat up. If your printer does this and you were to print without a purge line or skirt your printer wouldn't actually extrude any plastic until it the nozzle is filled again.

There's also the matter of the filament in your nozzle getting kind of scorched if it sits in there for a while.

They’re part of the start code, you can just remove that bit.

If you’ve started cold, there’ll be some ooze, and some a void. The purge line clears thst and wipes the strand from ooze (with in reason,). The skirt loops kind of serve the same purpose as well as checking g layer height

What are purge lines for?

To purge the system?

The point of purge lines is to make sure that the nozzle is properly filled with molten plastic, and that there's nothing stuck in it.

If you're printing with a skirt or brim, you can probably print fine without purge lines. If not, there's a chance that your first layer starts off with a defect.

If you really want to remove it, your slicer should have a Start G-Code section that is added to every print. If you know what you're doing, you could edit part of that out.

New Lemmy Post: Purge lines (https://lemmy.world/post/9945761)
Tagging: #3dprinting

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