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I tried out printing a "bridge" for the first time using this Bridge Calibration model. The model creator suggests printing, tweaking settings, and printing again until it works "properly."

My first try worked reasonably well, but the underside of the bridge is pretty rough and stringy. But I don't know what a "good bridge" is supposed to look like.

printed bridge

How smooth should the underside of the bridge be? Any suggestions for what changes I should make to my slicer settings? Here is what I have currently:

slicer settings for bridging

Here is a picture of my hotend on my Monoprice Maker Select Plus, as requested:

hotend of Monoprice Maker Select Plus

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  • $\begingroup$ Can you post pictures of your hotend / part cooling fan. If you don't have strong part cooling your overhangs will sag more before solidifying. $\endgroup$ – Perplexed Dipole Dec 13 '18 at 23:54
  • $\begingroup$ I'm using a Monoprice Maker Select Plus. I'll include a picture above. $\endgroup$ – Kenny Wyland Dec 14 '18 at 3:40
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The idea of the part fan is to cool the plastic as quickly as possible once it is extruded in order to keep it in the correct spot. The slower that the plastic solidifies, the more the plastic will sag when printing overhangs/bridges. The stock part cooling fan/duct on your printer, Monoprice Maker Select Plus, is not all that great and would probably benefit from an upgrade.

As far as the Cura settings you posted, you should turn off most all of those experimental bridge settings. Your printer will still be able to print bridges without the 'Enable Bridge Settings' checked. The only one that would be useful is the the 'Bridge Skin Speed' since reducing the print speed effectively increases the air flow on the extruded plastic. More over you are turning off the fan for the 2nd and 3rd bridge skin layers which will cause them to sag even further.

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A good bridging underside looks preferably like this:

Bridging bottom side view made by: Dave's Stuff - Dave Hylands

This means straight long lines that have minimally sagged out. Why long straight lines? If they are straight and do nut sag out much, it is far more easier for the next layers to build upon. Please look at the difference between the above image and your own image, it looks as though you are missing more layers as the first bridge layer failed for others to build upon.

The idea is to get straight lines of filament from one to the other side. Knowing that filament is hot when you extrude it, it is difficult to bridge large gaps. It is impossible to think that enough part cooling will be enough to prevent sagging of the filament and have a perfect finishing at the bridge, there will always be sagging strands of plastic there. The idea for getting a good bridge (for other layers to build upon) is that you you need to solidify the hot filament as fast as possible to reduce the sagging. It is often best to reduce print speed and making sure your fans cool the extruded filament strands rapidly so that they become solid and stiff as quickly as possible.

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  • $\begingroup$ I might just add a little: that the visual quality of the bridge matters if that side is visible in the final product, so how far you want to be able to bridge depends a bit on how the printed part will be seen and/ or used. $\endgroup$ – Carl Witthoft Dec 14 '18 at 15:20

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