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How to properly unload/change materials

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I have just got my Ultimaker 3 and so far I'm getting some great prints with no tweaking needed at all (an entirely different experience than my homebuild Prusa i3 clone)

The only thing I don't know how to do properly is unloading or changing filament. Every time I unload or change filament, the old filament is quickly retracted from the Bowden tube, but that does not seem to work properly.

Sometimes the filament is just stuck and the feeder grinds it.

Most of the times however, it does retract, but a small bit of filament that (I presume) was in the hotend is also retracted. This little piece (a few mm) is only loosely connected to the rest of the filament and always gets lost somewhere in the feeder and I'm not able to remove it. I guess it's down there somewhere, preparing to wreak havoc in the future.

So I'm wondering if I am doing this correctly.

Should I first heat up the hotend before unloading/changing filament? Is there some other operation that needs to be performed before unloading? Am I not closing down the machine correctly?

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At the end of a print, the filament is retracted to stop the flow. After that, the hot end temperature is lowered, after which another (large) retract is done. This is done to prevent exactly the effect you describe (a piece of filament at the end that is loosely connected to the rest).

How do you change the filament? Do you use the procedure in the user interface?

Do you use Ultimaker filament?

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I get this sometimes also. So I usually change filament manually. I just push down on the lever on the feeder and pull the filament out. If there is a little blob at the end of a string I hope it makes it through the feeder and 2/3 of the time it does. When it gets lost I don't worry too much - usually it sits in the bottom of the feeder. sometimes it gets back inside the bowden on the next insert and gets back into the nozzle. So far I don't think it's been a problem.

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At the end of a print, the filament is retracted to stop the flow. After that, the hot end temperature is lowered, after which another (large) retract is done. This is done to prevent exactly the effect you describe (a piece of filament at the end that is loosely connected to the rest).

How do you change the filament? Do you use the procedure in the user interface?

Do you use Ultimaker filament?

 

Tom,

I follow the UI, I mostly have problems with materials like ABS, PC

I usually get a blob and a string the length of the boden tube.

yes Ultimaker filament

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Here's my experience. I always used to retract the filament at the normal printing temperature. This would result in a long, thin string of filament on the end. With a J-head hotend this never caused a problem but on another machine that has an e3d v6 I suffered numerous nozzle blockages. I finally realised that I was doing the filament change retract with the hotend too hot because it caused the stringing that would then block the v6. So now I do the filament change retract at 20 deg or so below the normal temp (say, 180 for PLA and 200 for PETG), this stops the stringing and I have not had a blocked nozzle since. I know, that's a dumb mistake.

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This is for an UM2, but maybe it can be used for an UM3 too?

I disconnect the bowden tube at the nozzle, and pull the tube out. This breaks the thin strand of filament. Then I move the filament forward a bit, and I cut off the irregular tip like this:

DSCN5251.thumb.JPG.0fb04621832303211d12c08aa7c7d534.JPG

And then I manually pull the filament out from the back. Sometimes this can be done while the printer is on, but sometimes the motors block this, and I have to switch the printer off.

In this way I never have pieces getting stuck in the tube or feeder. Of course, I learned this the hard way. :)

Then I do one or more atomic pulls to clean the remains out of the nozzle, and replace bowden tube.

To load, I insert the new filament manually, which goes easy with the tip cut-off in an angle, and using "maintenance > advanced > move material" I move it until it fills the bowden tube and is extruded. Then a small retract. And that's it.

It is more difficult to describe than to do.

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At the end of a print, the filament is retracted to stop the flow. After that, the hot end temperature is lowered, after which another (large) retract is done. This is done to prevent exactly the effect you describe (a piece of filament at the end that is loosely connected to the rest).

How do you change the filament? Do you use the procedure in the user interface?

Do you use Ultimaker filament?

Yes, I use the unload or change procedure in the user interface.

I have this problem with both Ultimaker and other brand filament. I have only used PLA and PVA. The blob on a string happens with PLA. The only time I have used PVA, it was grinded when unloading and I needed to manually remove it.

I do hear some things happening after the print is finished. I'll pay a little closer attention next time to see if the retractions are happening as you describe.

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