Bondtech gears alginment in the *x* direction  

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peridot
(@peridot)
Eminent Member

There are many guides adivising us to make sure that the Bondtech gears are aligned with the filament path. Alignment in the y direction is straightforward: use the set screw on the Bondtech gear that sits on the extruder stepper to shift the gear back and forth until the filament path is straight from the opening above through the gears to the opening below. But I seem to have a problem with alignment in the *x* direction: when I open the door I can see the filament bending towards me to go over the gear and then back away to go into the PTFE tube below. During initial assembly I couldn't get the filament into the lower part at all, now I've rebuilt the extruder and the filament will load but I'm getting inconsistent extrusion. There doesn't seem to be any way to adjust the X position of the Bondtech gears - the extruder stepper bolts directly onto a plastic part containing the channel and holding the hot end, and already at this stage I can see the alignment is problematic.

Has anyone else encountered this problem? Any suggestions? I asked in the assembly manual comments and was told it was fine as the other Bondtech would compress the filament to make it fit (!), but I do see inconsistent extrusion.

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Posted : 02/07/2019 4:32 pm
karrie liked
vintagepc
(@vintagepc)
Noble Member

This is a known design flaw in the extruder design. A few community members have modified the original design to fix this, look for the "butterworth design" extruder.

https://www.myminifactory.com/object/3d-print-butterworth-design-prusa-mk3-mk3s-r4-extruder-mod-filament-path-alignment-and-indirect-mk3-filament-sensor-86329

Posted : 02/07/2019 4:49 pm
peridot
(@peridot)
Eminent Member

Thank you! I'll give that a try.

Now I just need to get either mk MK3S or my MK2S working adequately (heated bed just died on the MK2S)...

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Posted : 02/07/2019 5:25 pm
vintagepc
(@vintagepc)
Noble Member

You should be able to print fine with the stock extruder, if you're having issues with that then it's likely this is not directly the cause unless something is grossly wrong with your printed parts. 

Pictures of your inconsistent extrusion may help, that's a general term for any number of possible symptoms and origins. 

Posted : 02/07/2019 5:28 pm
david.a66
(@david-a66)
Honorable Member

yep it's a known issue with the prusa extruder design - there are a number of respins arounf that move the motor position a bit to line it up over the tube

Posted : 02/07/2019 5:36 pm
peridot
(@peridot)
Eminent Member

I'm getting occasional successful prints (a benchy appears to be completing, my standard calibration cat consistently fails) but the problem is apparent in a first layer calibration - the filament laid down varies from smooth and slightly flattened to bare strings. The frustrating thing is the printer was working quite well, even with the MMU2, until I broke a thermistor wire and upgraded to MK2S. Now I'm trying to get even basic prints working. (And the heated bed connector on my MK2S appears to be both open and welded in place.)

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Posted : 02/07/2019 6:55 pm
peridot
(@peridot)
Eminent Member

Here is the (a) trouble I am having. I have played with the extruder idler tension to no avail. I'm about to go through the printer maintenance checklist in case something is loose or I've forgotten something.

[caption id="attachment_2266" align="alignnone" width="300"] Irregular extrusion in first layer calibration[/caption]

 

[caption id="attachment_2267" align="alignnone" width="300"] Irregular extrusion in first layer calibration[/caption]

Sorry, I'm trying to figure out how the forum handles images. Not in the obvious way, I guess.

This post was modified 1 year ago 2 times by peridot
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Posted : 02/07/2019 7:12 pm
david.a66
(@david-a66)
Honorable Member

looks like your live Z height is way too high

Posted : 02/07/2019 7:21 pm
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