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LePaul

(Ultimaker Classic) Loading and priming PLA into head question

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I've never been able to find this in the manual / wiki so I thought I would ask here...

Last night I did a Torture Test print. It got to about 90% and the PLA material broke inside the extruder, just above the feeder/drive mechanism.

It was a little tricky getting the remaining PLA out. Recalling what GR5 and others had posted elsewhere, I heated the print head to 185. Since I couldn't get at the remaining PLA from in the extruder, I removed the Bowden tube retaining clip I had printed and the was able to pull the Bowden tube off. That gave me access to the PLA and pull it out of the print head.

With all the talk of clogs and "boogers", I was looking for the proper procedure to "prime" the print head.

Should I heat to 250C and let whatever is remaining in the printhead drain out?

Or should I assume that everything came out with the remaining PLA? (It had sat in the machine, off, for 6 hours)

Next...putting the material back in.

First, PLA is the most awful "Slinky" to work with. It doesn't seem to like to be on the spool. Last time, I just set the spool on the floor and let it pull up the filament as it printed. But since I had that breakage, that won't work.

Second...am I the only person who nearly goes insane trying to make the PLA slide into the extruder and into the bowden tube? It is always a struggle!

But...the material is in, the extruder is clamped shut.

I heated to 220 and kept manually feeding (rotating the extruder gear) until I had PLA oozing thru. When the oozing ceased, I assumed the mat!)achine was "primed"

Is that how it should be? If not, can something be documented and placed in the documentation/wiki?

That would really be a good checklist item to have printed out (something us pilots are very used to!)

 

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Priming is simply making sure that chamber inside the nozzle is filled with plastic. This is usually done for you automatically at the start of the print when the machine squirts out a bit of plastic just before starting the print. This is done because when the head is sitting hot for a little while without printing some plastic will drip out, if you were to start printing immediately after this happened (without that extra little squirt at the start) there would be underextrusion until the head has filled back up with plastic.

When you change filament just keep feeding it in until plastic starts coming out in a steady stream and you're done. If you are changing to a different colour you'll have to keep extruding plastic until you have "washed out" the old one from the head. This can be done by manually turning the gear or by printing a small "throw away" print (if you're lazy and don't want to extrude manually :) ). How long it takes depends. Going from black to white will take longer as black specks/streaks are much more visible on white than say brown on red.

Unless you have an actual clog preventing you from printing/extruding you don't have to do anything special. You can leave the material sitting in the printer indefinitely when it's turned off, it might soak up some moisture after a few weeks but generally that's not something you should worry about. You shouldn't let it sit idle in the machine for long periods if the print head is heated up though, that can cause issues (so don't heat up the print head without starting a print and then walk off to have dinner).

Yes, it can be a bit of a slinky when the spool is full, it gets better as you get rid of a few meters.

If you cut the end of the filament at an angle to make it pointy and sharp and bend it a bit so that it is straight it will be easier.

I hope some of that made some sense, if not, keep asking away.

 

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With all the talk of clogs and "boogers", I was looking for the proper procedure to "prime" the print head.

 

An addition on Priming....

I usually try ( sometimes I forget) to prime every time a print starts.

Specially with repetitive smaller parts you better change the standard start- and endcode.

Might miss something, but how I read the code, I see in the end code a retraction of 6mm.

Startcode says

 

G92 E0 ;zero the extruded length

G1 F200 E3 ;extrude 3mm of feed stock

G92 E0 ;zero the extruded length again

 

 

that's A total of 0,0mm, so every time you start a new print you are 6 mm short of filament. Very Roughly 300mm printinglength? Exact mathematics are for Gr5 or illuminarti :)

So I try to remember to turn the extruder by hand before the print starts.

 

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Yes, the standard end gcode retracts 6mm, and the start code advances 3mm. So, yes, there's a possible imbalance. That said, a few loops of skirt will generally get everything flowing again - but it's easiest to do what I do, and just change the start gcode to extrude more plastic - 6mm, or even 9mm.

It would also be a good idea to lower the speed from F200 ( = 3.33mm/s) to something more like F100. As Robert pointed out, 1mm of filament is 6.38mm³ - so F200 is 6.38 x 3.33 = 21.2mm³ of plastic per second. That's a lot more than the head can extrude, so runs the risk of some filament stripping, or perhaps squirting some molten plastic where it shouldn't go.

 

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