How do I work out the correct Bowden tube length

I am just at the point where I want to connect my bowden tube to my extractor. I suspect it should be as short as possible but how to work out the correct length?do I just move the effector as far from the bowden tube as it will go then make it a nice smooth curve or is there a better way?

Ok, so my printer is 1m tall and the print bed is 330mm. As it is I think about 70cm - 75cm seems about right to me, the effector can reach every part of the bed without stressing the bowden tube so that has to be about right but I don't want to cut it and make a mistake.

As long as it can reach ever part of the bed, while keeping the tubing a bit lose you will be fine.
I know the feeling of cutting something and coming up short.
But a bit of slack isnt a problem.

So it looks like 65cm would be good but I cut it at 70cm just to be sure.

You may want to consider ways of making the Bowden tube shorter. If you currently have the extruder mounted on top, it can be located quite a bit lower (around 40%) without interfering with the arms.

My delta is also 1m high and the printable diameter is 300mm. The Bowden tube is 660mm long. I have two pieces of elastic supporting it from the top frame, to avoid its weight applying a tilting force to the effector.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ideally the shorter the better but it will work if its long, you just have more problems with filament control as the filament can stretch/compress and flex in the tube. This means that you get more blobs/strings etc... Retraction tuning is harder with a longer tube.

I'd recommend mounting the extruder halfway down the printer to shorten the tube. Or consider a flying extruder. There's a good thread on this forum about it.

Having an i3 with no bowden, and a delta which has recently gone from long bowden tube to short one via flying extruder the improvement in print quality is easily seen.

My Extruder is mounted exactly halfway down the printer but I wonder if it wouldn't be better mounted halfway between the base and the highest extruder position.

Should the tube be as straight as possible? For instance, mounting the stepper above the extruder rather than on the table top next to the printer, forcing a U-path in the tube.

Definitely need to shorten my bowden tube, just have yet to figure out a good mounting strategy for the stepper on a Rostock delta.

Everything being equal, the back-force goes up tremendously when you start bending the path, depends on the bend radius, material size and type, etc. Even teflon will have this problem, surprisingly so. Making the tube longer will relieve sideways stress on the effector but I am thinking the longer length will cause more friction, subtracting from the gain achieved from going to a wider bend radius. Also, the chewed side of the filament should have more friction than the smooth parts. Also, longer tube will also cause more hysteresis in your filament feed and force a greater amount of retraction.

After experimenting with different positions and angles of the extruder, for all extreme positions of the effector, I ended up mounting the extruder motor on one of the uprights about halfway between the bed and the homed position of the effector. The best angle was about 30 deg from vertical, so the tube actually shoots out away from the chassis some before coming back inside to the effector It is about 60 to 70 mm long as well, even though I am using 3mm filament. I use a rubber-band (actually a string of them) from the top of the back chassis tower to the top of the loop of the bowden tube to keep it pulled up and reduce side stress. The pull from the band is very weak, just enough to keep the tube upright.

Edited 1 time(s). Last edit at 12/10/2015 07:36PM by shadowphile.