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eldrick

Bowden clips to take up slack?

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I've been seeing increasing blobbing on retractions with my UM2, and I'm wondering if it is caused by visible slack in the Bowden tube. There is now about 1mm or so of space visible between the Bowden tube end and the clip at each end of the tube. When a retraction happens, you can see the tube pull up that slack as it takes back 4.5mm of filament.

If this is a probable cause, could a thicker clip take up the slack and reduce the blobbing and stringing that seems to be increasing? I'm thinking of remixing the bowden clip from Youmagine and scaling it to make it taller/thicker, in order to take up the slack.

Thoughts?

 

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yes. You can increase the 4.5 to 6.5 or you can lock in the bowden.

You don't need any clips. First a definition:

"bowden holder" - That thing on the print head that you push down in order to pull up and remove the bowden. It has 4 metal blades inside that dig into the bowden. The little colored clip goes under it. It's off-white colored.

Simply loosen the 4 long thumb screws such that the print head relaxes about 1mm. Then push down hard on the bowden (the bowden holder allows one way movement). I guess I would remove the clip first but it shouldn't matter. Then screw the 4 long thumb screws tight again - make sure no wires get stuck in the gaps when you are done (inspect all 4 sides of the black print head - black seams). Now the clip should be useless and the bowden should be tight. If not repeat but go 2mm relaxed instead of 1mm.

I did this and was able to lower my retraction distance back to 4.5mm.

 

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No, let it stick up, that's what makes it grip the tube properly. The problem is that the "roof" of the head is too thin. The purpose of the horse shoe is to push the collet up and lock it into place, ideally the horse shoe should just barely fit under there. But since the "roof" is so thin the collet has a lot of room to move even with the horse shoe in place.

Look at the feeder on the back of your printer. Notice how there's a raised ring around where the collet sits to take up the slack?

 

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Some day you will damage your bowden with the 4 blades in the "bowden holder" and it won't stay up any more. Only when that happens should you cut off a few mm of the bowden. But the bowden holder will still "stick up".

 

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I took the Ultimaker 2 Bowden Clip from Youmagine and scaled it taller in Z in Cura. I made several horseshoe clips ranging from 2.0 to 3.0 times taller and tried them out under the Bowden holder until I found one that just fit.

It had the intended effect - the bowden tube now stands straight up at the head, so the filament has a lower-friction path at entry.

With that and another one under the bowden clip on the extruder, blobbing is a thing of the past - it's back to new performance, aside from major underextrusion.

 

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