Lift during travel?



  • I wouldn't consider this on my core-xy bot due to all the bed lowering\raising it would require, but on my delta….

    Is there a method that would allow you to 'lift the nozzle during a travel move'? There have been times during travel moves that the nozzle will catch on some piece of the layer below it causing issues. Sure, you could argue that those issues should be resolved. But on the flipside, a feature like this could sure be handy.
    Sort of like Simpliy3D's 'Retraction Vertical Lift' option, but for travel moves.

    Doable as is, or would requires some sort of future firmware upgrade? Or would this be more in the realm of the slicer software, and not the firmware?


  • administrators

    Lift is normally configured in combination with retraction. I think all the major slicers support it.



  • If a retraction is commanded then you can specify z-hop or lift, and the amount, either in your slicer or in the firmware, however, lets say you are infilling the first layer, after one section of infill has completed, sometimes the nozzle will move to the next and not lift, as no retraction is commanded, only a fast move. This is certainly a behaviour slic3rPE exhibits. In most cases when I see this I conclude it is a time-saving feature as a small string (or mark if slightly over-extruded like on a squashed down first layer) across the infill will not aesthetically affect the model and a retraction would slow things down.

    I'm not sure I've ever tried to turn it off, and force retractions for all non-printing moves, or whether I can , or would want to.

    In fact the only argument I've seen against fast travel moves, is that they are too fast to melt their way through any prominent filament from the previous layer, and therefore more likely to create an impact. Otherwise fast travel moves make sense on a lot of other levels.



  • @DjDemonD:

    sometimes the nozzle will move to the next and not lift, as no retraction is commanded, only a fast move.

    See also the 'Only retract when crossing perimeters' setting on the advanced panel of the Infill settings. AFIK this is the setting that toggles this. (Slic3r)



  • @DjDemonD:

    the only argument I've seen against fast travel moves, is that they are too fast to melt their way through any prominent filament from the previous layer, and therefore more likely to create an impact. Otherwise fast travel moves make sense on a lot of other levels.

    Amen, working on making sure nothing is sticking up (eg speed, extrusion and other calibration) is probably a better way to 'resolve' this then relying on the nozzle to blunt-force it's way from A-B.



  • So, to be clear: I want to lift on travel moves only: I don't want this tied in any way to retraction. There is a lot of hoopjumping you can do in S3D to sort of simulate this effect, but again, it's still tied to retraction.
    For example, if I disable all retraction, I still would like to lift nozzle during travel.
    This was brought up in the S3D forums, and I agree with all the points the author brings up:
    https://forum.simplify3d.com/viewtopic.php?f=23&t=8525&hilit=lift+during+travel

    Based on all my reading this sounds like it's 'not a thing' in firmware or in slicers. I feel the place to do this would be in the slicer itself, but getting the S3D devs to do anything is impossible.

    But on the flipside, I could envision this being done in the firmware as an option for G0/G1, in the same way you can use M376 to taper the bed compensation over time. Meaning, it wouldn't immediately just 'jump up 2mm' every time it travels, but ramp into it over a distance, then ramp out smoothly. Presuming the slicer can differentiate between travel moves: Looking at the gcode S3D spits out, it's all G1's. Small use case, probably never happen, but I can't imagine it hurting anything.

    Example usage: When I print with a 1.2mm volcano nozzle, any slight print artifact in fact becomes quite a large one, and the nozzle can catch on it while traveling around. On a .4mm nozzle the same artifact may be present, but it's so much smaller relative to the toolhead it just gets melted out of the way. But on the volcano, I've had whole prints shift by being caught during travel (meaning, nozzle hits print, print is so well stuck to the removable bed, the removable bed ends up getting pushed around), because some random piece decided to curl up a bit and hit the nozzle. Again, arguments could be made that 'you should tune your print better', and I won't argue that. But tuning takes waaay longer than if this option was a reality.

    Not a need. But sure would be nice.


  • administrators

    All FDM printer technologies that I know of need to use retraction before travel moves, so IMO it's entirely reasonable for Z lift to be tied to retraction. If you have a magic printer that doesn't need any retraction at all, why not set the retraction to 0.01mm or some other tiny value?

    Ramping Z up and down during travel moves was something I considered adding to RRF several years ago, but the Z lift supported by slicers made it redundant. In any case, if you ramp the Z lift during the travel move, you could still catch the nozzle on a curl up close to the start of the end of the travel move.



  • I think there are edgecases that aren't being solved by conventional slicer settings: I can say 'only retract when crossing open spaces' in S3d (which is what I usually do). But it's possible based on the toolpath of a given layer, that the head may move around to different spots, but not crossing any open spaces, and thus travel without a retract. I don't care if a little ooze sticks to some of the infill. So even if I had the 'z-hop on retract' set, it wouldn't hop for that move, and could arguably catch on something in the process.


  • administrators

    Is there a downside to retracting on all travel moves longer than a certain (short) distance?



  • Can only speak for myself, but I've gotten far better quality not retracting on outer perimeters than retracting, in many cases. So I basically only retract when I cross an open space to remove that blobbing.

    But you know what, I've never actually tried S3D's 'hop while retract' while using my delta, so I may as well try (on my core xy the bed is then constantly lowering/raising, really slows things down). Maybe it will end up scratching that itch 😉



  • After some testing: The 'hop on retract' does get me what I'm after more or less. I end up having to retract more often than usual to pull it off (disable the 'only retract when crossing open spaces') which technically means things are slowing down slightly. But it's strangly cute watching the tooldhead bop up and down 1mm as it cruises off somewhere else in the print. Sure, I still think it'd be nice if this was entirely decoupled from retraction as it's own feature, but for the time being, I feel it's giving me what I want.



  • Slicers do seem to want to minimize Z travel wherever possible.. a hangup from all the XY printers with slow Z axes on leadscrews I guess

    With a delta printer the 'cost' of a Z lift during a move is minimal; so an option to put a hop on ALL non printing moves might be valuable. I can see edge cases where you might not want retract.

    • I'm thinking of weird filaments, maybe machines who's 'extruder' only goes one way.. Concrete FDM systems? Pancake printers? There must be some variations of FDM where you only ever want to move the extrudite forwards and never, ever backwards..
    • Having such a feature available, even if only as a 'support 0mm retraction with G10') option could be a nice feature to offer.


  • Agreed accurate deltas can do lifts and avoiding crossing perimeters etc much easier than cartesian machines.

    I wonder though if this is something which is a slicer function, maybe raise an issue with slic3r or slic3rPE teams asking for a z hop no retract mode. Cura might be interested, you won't get anywhere with S3D.



  • @Ak:

    After some testing: But it's strangly cute watching the tooldhead bop up and down 1mm as it cruises off somewhere else in the print. .

    I typically use .2mm which is plenty in my opinion


 

Looks like your connection to Duet3D was lost, please wait while we try to reconnect.