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bobstro
(@bobstro)
Illustrious Member
Tension-Free Filament Feed?
I’ve been very happy with the results I’m getting since moving my Mk3 into a 3/4 closed cabinet and mounting it on a paver. Everything is very stable and noise levels are excellent. The only thing I’m wrestling with is the filament feed. I have 3 spools mounted on bearing rollers on a shelf below the printer. I have a crude printed pair of rollers feeding filament from behind the printer and up over the frame with a small feeder with horizontal and vertical bearings. It all works, but I do notice a bit of noise sometimes as the extruder tugs on the filament and the spool rolls. I suspect the variations in tension are adding to variances between layers.
 
A fixed reverse-Bowden arrangement makes sense, with some sort of bracket on the lower shelf supporting a length of PTFE tube over the back and up to the top of the frame to keep the level of tension on the filament consistent, thus reducing the friction in the feed path, but two things concern me:
  1. Feeding 3 spools through a long tube in the back is likely to be annoying.
  2. The extruder will still have to overcome the friction of the spools on the bearing rollers.
I’m using Octoprint on the printer and notice that there is a continuous serial stream of feedback from the printer indicating extruder (E) moves. I’m wondering if buying an inexpensive extruder and mounting it on the lower shelf, then using it to pull the filament off the spools and into a smooth PTFE tube to the printer above would be worthwhile. It’s certainly an over-engineered solution, but I’m fine with that. I’d need to rig up Octoprint to echo E moves to the 2nd extruder, but that doesn’t seem overly complicated. Some sort of slop would be needed to account for variations. Loading could be accomplished much more quickly and without fumbling at the back behind the spools. Any thoughts on the merits of doing this?
My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Napsal : 02/11/2019 1:45 am
rmm200
(@rmm200)
Noble Member
RE: Tension-Free Filament Feed?

My solution works for me.

I use a single spool roller (that the spool sits on) using skateboard bearings on top of the Lack enclosure,

It feeds directly down through a double cone in the lid. Filament only touches at one point.

From there it goes directly down into the extruder. No noticeable friction I can see. Extruder seems happy with it.

Napsal : 02/11/2019 5:37 am
ACE
 ACE
(@ace-2)
Trusted Member
RE: Tension-Free Filament Feed?

I'm using auto rewinding spool holders and long bowden tubes from a drybox under the table to the MMU. originally I had friction issues but i finally was successful by switching to 2.5mm ID tubing.

Napsal : 03/11/2019 3:24 pm
timo.m
(@timo-m)
Estimable Member
RE: Tension-Free Filament Feed?

Hi Bobstro, I also use the reverse bowden setup. I designed and printed myself a small part which is attached to the upper right end of the frame. (I used longer screws to mount the top end of the right z axis and conutered the part with nuts. This rather flexible part reaches out about 80mm from the side of the frame and holds a pneumatic coupling. My spools sit on a roller bearing holder to the right side of the printer. I use good bearings and haven't had any problems with friction even with 2.6kg spools.

 

The flexibility of the bowden holder also helps with leveling out tension on the filament a bit. You can see it moving up and down slightly when the printer retractrs.

 

I guess you could easiyl build yourself a similar system which extends to the back from the top of the frame to feed multiple spools into it, by switching the bowden tube at the extruder depending on the filament for example.

This post was modified před 5 years by timo.m
Napsal : 04/11/2019 3:26 pm
JBinFL
(@jbinfl)
Reputable Member
RE: Tension-Free Filament Feed?

Bobstro:

I cannot take full credit for this suggestion, it was first posted by TIM-M30 previously, but I will take credit for bringing it up here 😀 😀 😀 ...

I have a LACK enclosure with a slot type guide in the top for the filament, the slot is approx 150MM wide - I got it from Thingiverse, and use a PVC tube filament holder for the spools...  Tim-M30 suggested in a thread to move the filament holder from a front to back enclosure orientation to a side to side orientation.  e.g. the spool holder is on the side of the slot instead of in front or in back of the slot the filament goes through.

It works surprisingly well and has eliminated the slight binding issues and creaking when the extruder is at the right most or left most printing position.  If possible, if you could orient your spool holders to feed to the sides instead of front to back, that could be an option to try.  Especially if you have a slot type opening for the filament to feed through on the top of the enclosure.

I think the theory is that the extruder moves side to side in a fixed place but is stationary front to back so no binding.  It works for me...

Again, If I could find the post in that thread, I would upvote it, but it was a couple of weeks ago so it is lost in the ether, but it was helpful to me... original credit to TIM-M3o for the suggestion, but to me for keeping it alive 😝 

jbinfl 

 

Strange women, laying in ponds, distributing swords, is hardly a basis for a system of governance!

Napsal : 05/11/2019 11:56 pm
bobstro
(@bobstro)
Illustrious Member
Topic starter answered:
RE: Tension-Free Filament Feed?
Posted by: @jbinfl

[...] I think the theory is that the extruder moves side to side in a fixed place but is stationary front to back so no binding.  It works for me...

That's a great idea. Unfortunately, the rack I'm using (19 inch audio rack) requires me to position the filament on the shelf below the printer, so I'm having to feed out the back, up to the printer on the shelf above and over the top of the printer. It works, but I'm sure the increased friction isn't helping my finish consistency.

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Napsal : 06/11/2019 1:32 pm
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