Retraction issues with bowden



  • Hi,
    I've got a long bowden (aprox 1m) with capricorn tube, Bondtech BMG extruder and an E3D Volcano setup. I'm using Cura and I find it really hard to get the retraction settings to work out good, I'm used to direct drive systems.
    I get alot of zits and so on.

    Does anyone have a similar setup that would like to share their settings?
    I'm using a 0.8mm nozzle atm.



  • @haggan90 That's a big nozzle and the Volcano has a large melt chamber so you getting it right will be a challenge. You will need to use a lot of retraction. I would suggest you use firmware retraction to tune it, if Cura supports it (I'd be surprised if it doesn't). You can always go back to using Cura but one of the main advantages of using firmware retraction is that you can change it "on the fly", which is much easier than printing endless objects with different settings.

    I doubt if pressure advance will help. With that size nozzle, and the relatively low speed that you will need to print at, it is unlikely that you will build up pressure that will need compensating for. It might be worth a try but put it low down on your "todo" list.

    Other things that would help would be to print at the lowest temperature that you can get away with and use a fast non-print move speed. The less time spent between moves means less time for filament to ooze.

    HTH



  • @deckingman Thanks for the quick answer!
    I got a fairly large print area, 500x500x800, that's why I want the volcano and a big nozzle.
    Would it be much easier if a use a 0.6 nozzle instead?

    I tried to get the firmware retraction to work a couple of months ago but coulden't figure out how to do it, I guess I have to try it again then.

    When I do vase mode prints it works out good, exept for a somewhat irregular layer thickness..
    I really thought it was a miss alignment with one of the 3 lead screws but after a re-design and careful measurments the bed moves down without any movemeant exept in the Z direction.

    Does anyone know what could cause this?
    Could it be that the pitch is 3mm?



  • @haggan90 I don't use a Volcano, prefering to use a multi-input hot end like the Diamond because it has multiple melt chambers and uses multiple extruders, each running at lower speeds. So, my input might not relative to your situation but I have played around with 0.9mm nozzles so maybe....

    For sure, a smaller nozzle will make life easier. You might find that print time is not too adversely affected because ultimately it comes down to the melt rate of the filament. So you can print at nnn mm^3 by using a large nozzle and slow speed, or you print at the same nnn mm^3 by using a smaller nozzle and faster speed.

    Irregular layer thickness could be that you are bordering on the maximum melt rate that the volcano is capable of. So try a slower speed and see if that improves things. Also, you need a huge amount of part cooling when printing large layer heights and thicknesses. If you have more air blowing from one direction, then that might affect layer thickness as you print around a circular path.

    3mm pitch (I assume you mean lead) is an odd number. I suggest you choose layer heights that are multiples of whole steps rather than relying on micro-stepping for positional accuracy. Assuming the lead of your screws is 3mm and you use 0.9 degree motors, then one full step will be 0.015 mm. So use layer heights that are multiples of this. Therefore 0.6mm would be good because it would equate to 40 full steps, but 0.5 would need 33.333 full steps and 0.7 would need 46.667 full steps. The latter two cases would therefore need micro-stepping for positional accuracy, which is not ideal.

    I urge you to try again with firmware retraction, just because it makes life so much easier for tuning., As I said before, this need not be permanent and you could always go back to using the slicer once you know the settings (but I think you'll find that once you have it working, you'll want to keep it). So in your configuration file, use M207. Then you need to configure Cura to use firmware retraction. I can't advise on how you do that because I don't use Cura but the end result will be that instead of Cura inserting G1 E-nnn values, it will insert G10 to retract and G11 to un-retract. Then when you are printing, you can use the web interface to change the retraction settings. You don't need to enter the entire command, For example, M207 Snnn will change the retraction amount but leave the retraction speed and other parameters unchanged.



  • @deckingman Thanks again for a great reply!

    I've seen your setup with the Diamond hotend, very impressive printer I might say!
    I can't say I find the volcano insufficiant at melting the plastic, I've tried printing at 40-60mm/s and it seems to work out fine. I really don't need to print any faster with that size of nozzle.

    Also I use a 50W heater for the volcano.

    Yes sorry, I mean lead.
    I've printed at optimized layer height for the 3mm lead.
    But I think the problem might be the steps/mm in the config file (1066.67).
    It seems!

    This is a vase print printed at 0.495mm and you can clearly see the diffrent layer thickness.

    Vase



  • if it is the 1.9mm capricorn tube this can cause problems when the filament diameter goes above 1.75. The increased friction can cause extrusion problems and the 1m long tube will further increase the problem.
    See if you can somehow shorten the bowden distance. By using a flying extruder for a delta or something similar for other setups.



  • @veti Hi,
    It's not possible for me to have a flying extruder unfortunatly.
    The printer uses a kind of double markforged kinematics with 2 independent extruders on the Y axis.



  • @haggan90 Well with 3mm lead and assuming 0.9 degree motors, then 1066.67 @ 16X micro-stepping is correct. But that is steps per mm so if you choose layer heights that are multiple of full steps, then it shouldn't matter. On the other hand, the pattern on the vase does look to be repetitive. So, as it is impossible to command a motor to move a fraction of a micro-step, them maybe the firmware rounds the steps per mm to 1067. In which case, that might explain the repetitive nature of what you are seeing. Just a guess....



  • @haggan90 said in Retraction issues with bowden:

    @veti Hi,
    It's not possible for me to have a flying extruder unfortunatly.
    The printer uses a kind of double markforged kinematics with 2 independent extruders on the Y axis.

    Two gantries similar to mine? (You need deep pockets though) ☺



  • @haggan90 said in Retraction issues with bowden:

    The printer uses a kind of double markforged kinematics with 2 independent extruders on the Y axis.

    you could suspend both extruders above the center of the x and y gantry. that should reduce the bowden length by a bit.
    here is what i did on an old version of my printer before switching do a direct extruder.
    0_1558615833603_IMG_20180921_140113-01.jpeg



  • @veti Thanks for the tip!
    THat setup actually made a huge diffrence 😃


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