Bridge settings and odd coasting-like behavior when coasting is off

[ablesser 0]

Hi folks,

 

I've been playing around with the bridging settings and I keep noticing something weird in the slicer.  Even when I turn off or play with every pressure-compensation feature I can think of (coasting, flow rate compensation, wall compensation, etc), nothing gets rid of these big fat extrusions at the end of a bridging move  (in this screenshot the extruder is moving in the direction of the red arrow as it draws the thin bridging lines.

 

It's as if there's some secret "opposite of coasting" line widening effect going on here that I can't seem to control.  Because my setup uses a printer with Pressure advance/linear advance, I don't WANT any sort of compensation like this to be fighting against the pressure correction that my printer's firmware is already handling.

 

What is causing these bulges ?  When I set bridge wall coasting to 0%, I was able to get rid of the "under extrusion before the bridge" (see second screenshot) but not this "over extrusion after the bridge" line .  The second screenshot illustrates my confusion where I understand the thin lines to be linked to the bridge wall coasting setting, but cannot figure out what setting could be affecting the bulges.

 

I'm not sure if this is a slicing bug or not.. but it sort of seems like it is ?

 

Thoughts ?  

[ablesser 0]

Higher quality images attached since the site is downscaling them above for some reason.

bridging.zip

 

Also, adding another visual example here to help make this clear.. when I turn coasting off and look at the preview in line-width mode, the thin lines before the bridge lines are printed (dark blue here) disappear, but the thick ones do not.. "why?" .

 

 

Edited April 7, 2022 by ablesser

[WhatWouldAnEngineerDo 0]

I had similar "issues", slicing the above model with the Arachne beta 2 slicer.

 

For some reason, the slicer seems to invoke one additional extrusion move at 1/2 of the Bridge printing speed, immediately after the bridge line has been drawn, and before the "normal" Wall line begins, which seems to be what is being drawn as an orange blob in the above graphic. 

 

I captured a series of screen captures in the attached .PDF, overlaid with the corresponding gcode from Cura.  Note that the F384.6 move is not created, if the experimental Bridge Settings feature is switched off.

I was not able to change this behaviour by changing any other setting in Cura (and I'm pretty sure I tried them all.)

 

As shown in the .pdf, I was able to make the blob disappear by modifying the geometry of the part but modifying the scale of the part only modified the scale of the blob. It did not make the blob go away.

 

Why the blob.pdf