Running without Bowden

[MichaelOToole]

Just realized, I been printing without the bowden tube for a long time (can't remember when or why I removed it).
I use a little piece of tubing to guide the filament entering the chamber from the spool but that's it...

Most videos show a bowden tube even with direct drive, I don't see the need, am I missing something?

 

[weaslus]

The purpose of a reverse bowden, is to keep the path the filament travels the same length no matter where the toolhead is. without one, what i have seen happen in the past is the toolhead can be pulled around during travel moves. As the toolhead nods, the nozzle raises and lowers. This leads to inconsistent first layer, and any other layer for that matter. Keep in mind, a 0.02mm deviation in the height of the nozzle due to pulling on the filament, is a 10% difference in the height of a normal layer.

 

[vinnycordeiro]

Just realized, I been printing without the bowden tube for a long time (can't remember when or why I removed it).
I use a little piece of tubing to guide the filament entering the chamber from the spool but that's it...

Most videos show a bowden tube even with direct drive, I don't see the need, am I missing something?

Filament friction can carve the part of the toolhead where it enters the extruder on a direct drive setup. Don't ask me how I know that...

 

[MichaelOToole]

Don't ask me how I know that...

... That makes perfect sense, will add a small piece of tubing there too, don't thing I need the full ...

 

[3dCase]

I have been running a short piece myself, just entering the filament sensor on top of the orbiter. But reading the comment of @weaslus , I realise this is a very good point. I will install a longer piece just to see if this accounts for some eratic layer lines I am sometimes seeing.

 

[MichaelOToole]

The purpose of a reverse bowden, is to keep the path the filament travels the same length no matter where the toolhead is

I see the logic however, it is also true that any object tethered to a moving body will cause restrictions to that movement.
It follows, a bowden tube is not very flexible, especially in compression and in the right conditions could cause issues....

Filament on the other hand is very flexible, it will not restrict movement except during the extrusion period (pulling filament from the spool).
In an ideal world we would feed the filament automatically from the spool end thereby removing any potential tension... I think there are low cost solution for this...

 

[3dCase]

I see the logic however, it is also true that any object tethered to a moving body will cause restrictions to that movement.
It follows, a bowden tube is not very flexible, especially in compression and in the right conditions could cause issues....

Filament on the other hand is very flexible, it will not restrict movement except during the extrusion period (pulling filament from the spool).
In an ideal world we would feed the filament automatically from the spool end thereby removing any potential tension... I think there are low cost solution for this...

Its not the flexibility of the tube or filament I think. When the printhead is printing clise to where the roll is, and uses up most of the loop of filament, when the next print length is on the far end, the head will move with high speed and yank the filament with a shock. This could cause problems as I see it.

 

[5twenty]

I think there are a few more cases of movement being made.

And 10x the OD is pretty common between most flexible's limit on how much you can bend...my filament would snap before my tube would! Yours is more flexible?

 

[3dCase]

I think there are a few more cases of movement being made.

And 10x the OD is pretty common between most flexible's limit on how much you can bend...my filament would snap before my tube would! Yours is more flexible?

My filament never snapped due to this movement but if I use wet or old filamend that has gone brittle, maybe it would snap.

 

[MichaelOToole]

Old filament snapped all the time without the bowden but with new filament this only happened once this year.
I guess this could have been avoided with a full bowden but even so, I just like the idea of running without the bowden...

Many machines use simple mechanical spring/lever tensioners setups to supply slack and prevent sudden movement from breaking fragile threads...

I currently use piano wire to support the umbilical cable, it works really well removing stress and allowing for sudden movements.
A similar approach might allow a predefined slack in the filament to prevent breaking during sudden quick movements...

 

[5twenty]

True, true. A ton of variables...as always.

What gauge piano wire are you using? I have some stiff wire that came with my canbus stuff, but I don't like how stiff it is, really stiff.

 

[MichaelOToole]

I bought 0.5, 0.8 and 1mm, I used the 0.8mm as 0.5 was a bit weak, and 1mm was a bit stiff (three bear selection process )
I made a loop on the free end to hold the umbilical cable and cut the length to position it about centered...

 

[5twenty]

I bought 0.5, 0.8 and 1mm, I used the 0.8mm as 0.5 was a bit weak, and 1mm was a bit stiff (three bear selection process )
I made a loop on the free end to hold the umbilical cable and cut the length to position it about centered...

Thank you. When I was looking this up last year I kept getting zero hits, and nobody was saying what they were using. Just a bunch of: "get some wire", yeah, no shit!

Appreciate it, this should help me get my umbilical in better shape on my son's before I do it on mine.

 

[lord-carlos]

With no bowden going out, would the extruder not YANK on the filament when moving away from the inlet? I imagine that could result in slight print quality deterioration.

 

[MichaelOToole]

This can be avoided or mitigated by making sure filament runs freely, in my case the spool runs on bearings.
The bowden in place doesn't prevent yanking, it tends to lessen the snatching / yanking by introducing a small elastic affect.
I will add a small piece of piano wire to mimic the same affect...

 

[lord-carlos]

Yeah, that would not work for my setup. I have my filament in a dry box, and PLA through a bowden from the dry box has a relative high resistance. ABS and PETG works better though.

 

[MichaelOToole]

I also used a dry box (Creality Dry Box 2) mounted on top of printer.

Initially I feed the filament out the outlet grommet directly but it kept sticking, I think they intended it to be used with a bowden tube as the hole in the grommet is sized to snugly accept one.
After adding a small piece of bowden the feed is silky smooth... It didn't help when the videos I watched of the dry box didn't use a bowden either.

I've even toyed with feeding the filament from the center of the top panel (drilling a small hole and using a piece of bowden tube from box to a pneumatic coupler screwed into the top).