What is the maximum bowden tube length admissible?

Hello,

I don't found any informations on the net.

For the moment I use 1.75mm filament (so 4mm OD, 2mm ID) and a bowden with 600mm PTFE tube. The thing work really well, but I want to add cable chain on my printer but the lenght will be >1meter now.

What the length of your bowden setup? Is anybody have try 1meter or more? if yes that thing work or not... some lantency at each line start?

I just want too now if I need to found a solution for shorten the tube a maximum and change the setup for my coldend extruder or if 1meter of PTFE is ok.

Thanks you very much for all your knowledge on that

I tried 1.2 meters, and my extruder was having issues pushing filament at times. I trimmed it down to about 700-800mm, and haven't had a single slip yet on either PLS or ABS.....

I am using 1.75mm on my OrdBot. I tried to keep the Bowden tube as short as possible at 350mm.

If you thread the filament through the tube and push and pull it at one end, you can see how much hysteresis there is. I am using a geared Greggs Wade extruder and the force on the filament is quite considerable. I also use a lot of retraction.

I am mounting the tubes at the center of the machine, above the top. More important than length is to minimize the angles of your bends, as it is the cusps and apexes of the bends that have the greatest amount of friction.

On Tantillus with 3mm filament I found 650mm was fine and at 800mm it is hard to get retractions to be effective.

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oH! very nice responses, thanks you very much for everybody

But it's my own experience too. So 600-800mm seem to be the longer bowden for 1.75 and 3mm.

So i need to redefine my nice cable chain carriage ... it's really a fu**** bad new for my full enclosure.

A slicer who take that parameter for anticipating the "hysteresis" will be greatly appreciated. Or an equivalent to advance parameter in marlin or repetier that works without I'm tearing my hair out trying to configure that....

Thank you, I find this conversation very interesting.

I am wondering, so when you get longer bowden cable, what turn out to be the bottleneck of the system: is it the hysteresis or the force required to push the filament?

For the hysteresis I don't know, but if you need more torque, there is always a solution.

Quote
dewasa
For the hysteresis I don't know, but if you need more torque, there is always a solution.

My extruder has more torque than the filament has grip. All metal, geared stepper, and Mk7 hobbed gear...not much room for improvement without changing to a screw or track drive mechanism.....

Or put two stepper in serial with mk7 hobbed gear and a sort of clutch for one motor only... Yes over priced and over complicated ... need another solution

Quote
zelogik
Or put two stepper in serial with mk7 hobbed gear and a sort of clutch for one motor only... Yes over priced and over complicated ... need another solution

What you mention is similar to what is done on wire feed welders when welding aluminum. shouldn't be super complicated and would be good solution for a LARGE printer.

How about a slightly larger diameter hobbed gear, and using multiple pinch rollers to force the filament to increase its contact area to something like 90 degrees of the hobbed gear's face?????

@vreihen: Somebody have already done that (I think I have seen that on thingiverse). The main problem is: larger diameter = more torque needed, less precision/step, so need geared motor, and you bend the filament too much. If your filament is brittle, you can have problem of break that filament.

What about a cascade of two extruders? If you put two one after the other and the two steppers are wired to the same driver, then wouldn't it double the tork ? And a simple extruder is cheap: stepper, gear, V bearing, spring and few printed parts.

Or another solution would be to put two gears :each pressing on one side of the filament. Each bolt having its own stepper, both steppers facing each other. The design might take some space, however, I guess it's not an issue on bowden designs.

vegetable oil/peanut oil or similar helps a lot on a bowden tube......Don't go too crazy with the oil, or your prints will smell like french frys...

Sorry to wake up the topic (after 6 months).
But this post can be useful to anybody.

After many many prints (long/short etc...), a 1.75 filament inside 900mm of 4OD 2ID PTFE tube is perfect. Even the path have "small" diameter, and no problems at all.

I have just installed a 1/5 motor reductor on simple nema 17.

There is almost no "hysteresis".

@+

zelogic:

Very interesting. I am using 1.75mm filament in the same size Bowden tube as yours, but mine is shorter - about 350mm long.

When I manually push and pull the filament backwards and forwards, there is quite a bit of hysteresis. I can see it. It requires a lot of initial force to get the filament to move, after all the filament is 1.75mm and the id of the tube is 2.00mm, so the effect is that the filament "snakes" inside the tube, due to friction I guess.

I am using a Greggs Wade extruder and the pushing force on 1.75mm is quite considerable. I can't hold it by finger pressure, so greater extrusion force is not required, imho.

Hysteresis means inaccuracy in the print, but is only a problem if there is successive backwards and forwards movement of the filament in the Bowden tube during the print. If the filament is continuously extruded in the same direction there would not be a problem I think.

How to minimise the effect of hysteresis? Less retraction maybe? Less stop/starts? Less lifting of the nozzle? Maybe this can be accomodated in the slicer software - a setting for Bowden tubes?

To minimize the effect of hysteresis, I have only 6mm of retractation with 120mm/s speed. no lifting nozzle, and slowed print speed and acceleration (yes really).

If I print at 150mm/s and 10000mm/s², I have too much hysteresis at start, so I have only putted 80mm/s (for infil AND perimeter) and reduce the accel to 3000mm/s². And my print are almost perfect, for big things or small details. Travel speed to 200mm/s.

So yes I have little hysteresis, but only at the start of the print, after that there is always some pressure inside the bowden/nozzle during the print process.

1100mm bowden, no problems with 1.75mm filament.
You just need a strong extruder.

As for retraction, I only use 5mm.
You need less distance if you can retract it fast. If your retraction is slow, expect to use more.