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Joined: Fri Feb 02, 2018 2:29 pm

Bridging - Extra Inflation Distance for Perimeters

Sun Mar 10, 2019 5:54 am


i notice that in Simplify3d v.4.1.1 the "Extra Inflation Distance" in the Other/Bridging menu does not affect the perimeters of a bridge.

You can see this here:
As you can see in the attached factory file, "Apply bridging settings to perimeters" is activated and you can see that both perimeters and infill of the bridge are recognized as bridges. They also both use specified bridging extrusion and bridging speed multiplier. However, the "Extra Inflation Distance" is only applied to the bridge infill but not to the bridge perimeters.

This is causing a real hassle to me: when the nozzle leaves the solid "base" (green+blue in the picture above) to print the bridge infill, it immediatly slows down to bridging speed. However, the pressure inside the nozzle is still high from printing the solid "base" with higher non-bridging speed and higher non-bridging extrusion mulitplier. The slow speed and the high pressure cause the line of plastic to just sag down instead of beeing pulled across the gap.
The bridge infill works just beautifully because of the working extra inflation distance. The pressure inside the nozzle drops to bridging levels while still on the solid "base" and when the gap actually comes, speed and extrusion match perfectly so that the line of plastic is pulled across the gab without sagging down.

I believe this is a bug and should be fixed: the Extra Inflation Distance should also affect the bridge perimeters. Does anyone know if they are working on this? Does anyone know a workaround?
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Re: Bridging - Extra Inflation Distance for Perimeters

Sun Mar 10, 2019 6:18 pm

Sorry, I don't see any issue!
The 3 perimeter-lines are running without a break to build the outside wall of the model and only the coloring doesn't play a role. As long as the permiters have the function as bridge, the color is yellow and when they have contact to the column they change to what they are in reality, inside or outside perimeters, colored blue or light blue.
The next layer above is totally normal.

How the real print is looking out?


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Re: Bridging - Extra Inflation Distance for Perimeters

Mon Mar 11, 2019 12:53 pm

Hi, thanks for looking into this with me.

Here you see a short clip of a few critical moments of the print: ... p.mp4?dl=0

Please report if you have any issues viewing this video.

My analysis of what is shown in the clip:
the perimeter is printed before the infill. So when the nozlle is about do do the first line that crosses the gap, it is filled with molten plastic that has a relatively high pressure in it. The pressure has to be relatively high because of the relativly high speed and relatively high extrusion multiplier that is used for the solid base.
When the nozzle leaves the base and moves into "the void", it almost imediatly slows down to bridging speed. But because of the high pressure inside the nozzle and nothing but emptiness below the nozzle, a string of plastic just "shoots" down. If i watch the part beeing printed i can see how this very first line sags down.
All following elements don't sag down. Even the other perimeters don't sag down because after printing the first bridge perimeter line there are only a few millimeters of solid base perimeter before the next bridge perimeter is printed. The pressure inside the nozzle doesn't rise to problematic levels during these few millimeters, so that the next bridge perimeter is printed nicely. However, you can still see that the second and following perimeter lines sag down more than the infill lines. This is because of the extra inflation distance that helps get the pressure inside the nozzle down.

Do you come to a different conclusion?

The next two pictures show that extra inflation distance does not affect the speed of the perimeters. I think it's safe to assume that it also doesn't affect the extrusion multiplier of the perimeters.
I don't think this is the way it should be. I think "Extra Inflation Distance" should also affect speed and extrusion multipliers of a perimeter bridge. Do you disagree?

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Re: Bridging - Extra Inflation Distance for Perimeters

Mon Mar 11, 2019 1:57 pm

Looking at your video, one thing springs to mind.....with a bridging speed of one third of normal printing speed, I'm not surprised you're getting sags when bridging!

Personally, I don't agree with your theory and the conclusions you've come to....and do not think any changes are needed in the software. I do think, however, you need to tune your settings to suit the material you are printing and the capability of your printer. Or use support material. With your printer settings correct, support will come away with little scarring.

But there again, I'm no expert, so perhaps I'm speaking out of turn.
Doug Kightley
Volunteer at the National Tramway Museum
Railway modeller and webmaster at

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Re: Bridging - Extra Inflation Distance for Perimeters

Mon Mar 11, 2019 2:45 pm

Every line, except for the first perimeter line, is printed perfectly. Even distances of 7 cm are no issue - if it wasn't for the first line of the perimeter:
It's always the first line perimeter line that sags down while all others stay up. I believe it is because extra inflation distance is not applied to bridging perimeters.

If you don't agree with this i'm curious what your explanation is why the first perimeter line fails and all other line succeed.

Also i'd like to know why it should be helpful to apply the extra inflation distance to the infill but not the the perimeters of a bridge.

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