Single line bridges are printed twice

[gauthier 0]

I created a model to calibrate the speed and flow of bridge walls. The goal is to print a single line bridge, and make it as good as it gets before going to bridge skin.

 

I expected the printer to print a line then go on. Instead, it prints the line a second time at the same position as the first line. It is problematic, because the second take goes over the first one, and since it isn't hardened yet, it often knocks it down.

 

The gcode looks like this (my added comments after #):

;BRIDGE
G1 F900 X99.325 Y92.107 E143.50126
;TYPE:WALL-OUTER
G1 F1200 X98.325 Y92.107 E143.51689
G1 F1500 X97.325 Y92.107 E143.5294
G1 F1725 X96.675 Y92.107 E143.53647
;TYPE:WALL-OUTER
;BRIDGE                         # First take: X96 to X76
G1 F900 X76.325 Y92.107 E143.69557
;TYPE:WALL-OUTER                # Some kind of anchor in the holder
G1 F1200 X75.325 Y92.107 E143.71121 
G1 F1500 X74.325 Y92.107 E143.72372
G1 F1725 X73.7 Y92.107 E143.73052
G1 F2400 X73.7 Y92.057 E143.73091  
G1 X74.763 Y92.057 E143.73209
G1 X76.325 Y92.057
;TYPE:WALL-OUTER
;BRIDGE                         # Back to X96! Same Z, Y is very close to the first take, 0.05 mm.
G1 F900 X96.675 Y92.057 E143.75482
;TYPE:WALL-OUTER
G1 F1200 X97.675 Y92.057 E143.75706
G1 F1500 X98.675 Y92.057 E143.75884
G1 F1725 X99.325 Y92.057 E143.75985

 

Is this the expected behavior for bridge walls, or is there something else that is wrong?

 

I've tried to change the width of the bridge lines in the stl (source in onshape), but even with the lowe st value that still appears in the slice, I get this double take (0.40 mm width is not sliced at all, 0.41 mm slices with double take).

 

UM2_bridge test.3mf

 

UM2_bridge test.3mf

Edited January 10, 2022 by gauthier

[gauthier 0]

Temporarily solved by making the bridges two lines wide instead of one. At least they don't mush together on Y. On the other hand I have to be there to watch the actual start of the lines, because the second line covers the first one.

 

So I'm still wondering if the single bridge wall line being printed twice is by design, and if there is a way to get rid of it.

Edited January 10, 2022 by gauthier