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Extruder of UM2

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The extruder of UM1 is easy to maintain because it is easy to disassemble it and clean the internal. Also, there is a screw to adjust the pressure on the filament.

The design of UM2 extruder looks very different. Is it still easy to disassemble to clean it or adjust it? Thanks.

 

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It's pretty easy to disassemble - only 4 screws - but then the motor wants to fall so I guess there is a 5th screw to remove the motor cover access.

The spring is too strong so everyone uses the loosest setting. I think UM will come out with a weaker spring so there is more control but right now the loosest setting for the extruder is about right.

The coolest thing about the UM2 extruder is that the firmware (and gcodes) can control the current. So you can set the current to a threshold below where the extruder grinds the filament. So what happens is if you have too high a pressure, the extruder skips steps backwards instead of grinding the filament.

On the downside - it's weaker than the UM extruder. And some people are blaming it for underextrusion issues (completely convinced!) but to me it's not clear where these people's underextrusion issues are coming from so the jury is still out. Also it is made of ABS and gets worn slowly over weeks of use and very tiny pieces of ABS can get into the nozzle which can also cause problems. Maybe. No one knows.

 

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On your last paragraph there gr5. Filament from spool -> extrusion test fails at 4mm3/s. Same filament straightened to reduce friction inside bowden and extruder -> extrusion test fails at 8-10mm3/s. The only change is the curvature of the filament which makes it kinda hard not to suspect the extruder...

 

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Can confirm it's counter clockwise... but honestly the spring is so strong... I doubt it could make any difference.

Also even with the spring at the loosest setting, the bearing is already making contact with the casing

There may be some adjustment/play in the 4 bolts themselves and you may sort this out slightly playing with this, but I didn't check that. I dismantled mine for the horrible squeaking noise I had, and can confirm the motor will fall... but was very easy to refit

 

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The only change is the curvature of the filament which makes it kinda hard not to suspect the extruder...

 

well - or the way the filament is mounted and fed to the extruder maybe? Is that really the extruder that is the issue or the way the filament reaches the extruder?

Although your design with the open extruder bottom seems to blame the problem and fix on the extruder. I love that idea by the way.

It's just semantics I suppose.

 

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gr5 you mention changing the current for the extruder. Where is this done? I am having problems with the extruder skipping backwards. At first I thought it was slipping on the filament but now I guess it is the program doing this. I have the extrusion set at 107%. Setting the temp of the PLA to 250C helps but I know this is too high. The result is pockets or holes in my print. I have a photo but can't figure out how to include it.

 

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To post a photo first go to the top of this page and click on gallery, then upload. Later make a post and to include picture click on "my media" next to smile face.

 

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If you are at 250C and extruder skips you should slow down the print. You can simply reduce the "feed rate" from 100% to say 80%. Or slower. Increasing the flow will make things worse.

 

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IMG 0399

Here is the photo from my extruder over current problem. I followed your instructions gr5. but if the above link doesn't work look in the gallery for "Extruder over current retraction gaps." You can see the gaps and holes in the print. The topmost layers are where I had the temp set to 250C. You see the change in shininess and there are almost no gaps.

Knowing now that the problem I was having was from too much extruder current I looked into other issues. I cleaned the extruder mechanism - it really seemed ok. I then completely disassembled the nozzle and cleaned it as best as I could. I heated it up to 230C and used progressively larger drill bits to ream out the nozzle. (Only slightly burned my fingers.) I quit with a bit diameter of 1/8". I then used a needle to clean out the nozzle tip and finally used a copper wire strand that measured .37mm.

I have the extrusion level set at 107% because when flat layers are printing at 100%, and it is filling in the area with parallel rows, I noticed there are very small gaps between the rows. These gaps are large enough that if I printed a cup it would not hold water. It's almost as if Cura moves the nozzle over .405mm for each row. I suppose it could be that the nozzle is slightly smaller than .40mm, but then the .37mm copper wire wouldn't fit. 107% squirts enough out that these gaps go away although I can still see the individual rows.

I think the problem originated when I was printing PLA at 260C. I was VERY happy with the finished look - nice and shiny with layers fused nicely. I went to work with the printer still going. My wife later aborted it when she noticed the nozzle had plugged and there were drops of black goo on the print that smelled burnt. I guess I cooked the PLA. When I cleaned out the nozzle I got quite a bit of dark goo out. I suspect this goo was making for poor heat transfer to the PLA I was trying to print in the photo above.

6 weeks now and I still havn't figured this thing out. Why does everything have to be so hard? :???:

 

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I'm pretty sure if you contact support.ultimaker.com they will send you a new nozzle for free.

If it were me I would purchase some THF on the internet and leave the nozzle in a cup of it overnight.

 

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I purchased the silver in the print from makershed, against the recommendation of illuminarti in the lead time update forum. The places he suggested were out of any colors I wanted. That may also be partially to blame. After the cleaning I printed a part with the filament that came with my UM2. Perfect results. I previously had good results with the makershed filament until I cooked it.

How about acetone. I can get that just about anywhere.

 

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