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eldrick

Cura feature request?

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This sounds like a really good notion: https://www.thingiverse.com/thing:559369

 

The idea is to slowly increase the movement speed at the beginning of a path and slowly decrease it at the end of a path, to ensure that the slack takeup and relaxation of the Bowden tube does not influence extrusion. I don't know how well it works, but it sounds good.

 

Thoughts?

 

 

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I think that slicers and/or firmware could be more intelligent for sure, but I'm not sure that that thing isn't just more or less the same as acceleration, though, contrary to what the blurb on the page says? Perhaps it isn't described as well as it might be.

What is needed, I think, is to decouple the extruder from the x-y motion, so that pressure build up/release is managed. E.g., Finish extruding early on a layer, so the pressure dies down before the z-change or move.

Simplify3D has a concept of this called 'Coasting' which works really well. For instance, in the double-wall cup, shown below, I set the coast distance is just over 2mm, leaving an apparent gap in the wall around the z-scar area. The head passes over that gap, but not actively extruding. The pent up pressure oozes into that gap anyway, so it closes it just fine, and then when the head pauses to change layer, there is less scarring as a result. It's a crude control, but quite effective.

Simplify3D Coasting

 

Marlin does have some code in it that is supposed to try to model and manage the hysteresis effects and pressure in the Bowden tube, and compensate for it, but I'm not sure if it actually works - it's not used in the current UM firmware.

 

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How about this feature.

When nozzle finishes the perimeter and needs to move away from it (say a sircle) it sometimes moves backwards from drawing direction.

Instead, make it move couple of mm's forward (which ever forward it went) to prevent cutling up.

For example.

New JPEG image

Black is the filament

Green is the nozzle path

Red is when path aproachign the end and travels to new location

(NOTE I did not mark travel with a different color, sorry, its all red and shoudl be obvious anyway)

Notice how sharp path changes ? When it does that, it tends to pull some filament off the end causing a gap or even tare it off the bed (depending what you print on)

The proposed part of the picture suggests to add aditional "move over/wipe" (without extrusion, perhaps retraction) over the surface to "seal the deal" before changing perimeter.

It wouldnt be such a big deal if perimeter would finish complitely before changing to another perimeter (if there were more then 1 black lines making up the perimeter) but this feature would still play a role in increasing the quality.

Its more obvious when printing ABS. I see gaps in those areas allover because i print objects with many many inner perimters etc.

 

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Marlin does have some code in it that is supposed to try to model and manage the hysteresis effects and pressure in the Bowden tube, and compensate for it, but I'm not sure if it actually works - it's not used in the current UM firmware.

 

It used to only work with direct drive, and went crazy when used on bowden tubes. But with all the changes in the code, it might even be broken now. (Direct information from ErikVdZalm, who implemented this feature)

As for the above proposal with pressure buildup&release has been in my head for a while. As it could also be very useful for multi-extrusion. But there are quite some cases to consider. As you do not want to do this on every print line (example, infill lines are printed with small moves in between. You don't want to release pressure between those lines)

As for the change of start position, I think this will make the prints worse, as the scar will be on the side of the print instead of the corner.

 

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It only needs to happen at 1st and last layers and only for perimeters.

I didnt propose start position change, starting at the corner is fine, i proposed slight (no extrusion) overrun rather then straight up move-away manouver.

It wouldn't be so bad if perimeter would finish entirely. If perimeter would finish entirely before switching to next perimeter (as i keep crying about for so long) then my proposal would only make sence for single line perimeters, which are rare and only used for either test or very small prints with small nozzles such as 0.2mm.

 

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