3D Printer Bridging: What you need to know

In 3D printing, bridging is when your 3D printer prints out an even, horizontal piece of a model in mid-air to join the two raised points. Bridging means your 3D printer prints between two points which are not connected.

                                                                                                                                                                                                                                                 Bridging problems are common; thankfully, they’re relatively easy to eliminate.

Bridging in Details

The 3D printer has to print in the air so the gaps can be bounded. Usually, when printing mid-air, one of the parts on an Ultimaker would have a flat line on its back, which would be the one being bridged. For that kind of join, though, it is probably easier to just use the tech help and close the gap. You will see in a single print what bridge lengths are challenging to the printer.

Try printing this bridging test. At first print, you’ll be able to see what bridge lengths are problematic for your printer. 50- to 100-mm bridges are good, while bridges spanning 150+ mm are excellent.

Why is Bridging Poor?

Poor bridges are prevalent errors when printing in 3D. It happens all the time when the extruded filament does not have any support material, or there is a lower layer of the object below the extruded filament, and the printing settings are not finely tuned.

Often, people want to avoid using support structures as it causes higher filament usage and longer print time. Also, the attachment of the support structures usually needs to be smooth. If your printer handles support well, you will save yourself from many such supports.

The unfortunate part of bridging poorly is that it will often destroy your whole project. This leads to a lot of frustration. Fortunately, there are easy solutions to the issue. The primary reason for the bad bridge is the poorly calibrated printing settings.

Increase Cooling

To make sure that the line of plastic in the lower layers of your bridge sticks to the columns nicely, it is essential to do a little bit of over-printing. By using a slower printing rate, the plastic will have more time to stick properly to the pillars, resulting in better stackability. With a lower print speed, resin layers will have more time to bond, and your deck will be more attached at the other end.

You need to raise your fan speed if you want better bridges out of the prints. In addition to flow speed, increasing print speed will impact bridging quality. Lower temperatures, a better cooling setup, and increasing retraction settings can prevent spongy 3D prints that could cause the bridge to appear unwieldy.

When customizing your printer’s bridging capabilities, increase print cooling (print fan speed). If you’re printing bridges with a low print cooling setting, the filament will just sink into a big mess of molten plastic. So, start at 100% fan speed, and keep an eye out for bridging improvements.

However, if you’re noticing clogging or poor layer adhesion, your fan setting must be too high! Bring it back down in 5% increments, and move on to the next easy fix.

Decrease Flow Rate

For material to cleanly bridge a gap, it must set quickly. So, if too much molten filament flows from the nozzle, it’ll have no time to settle.

By decreasing the Flow Rate or Extrusion Multiplier in the model slicer, your printer will be able to extrude a steady flow of filament that can cool into a beautiful bridge.

The 3D printer adds material in-between raised areas, creating a bridge placed above the material deposited underneath. If a support structure is selected, the first filament layer of the bridged sites is printed over the top layer of the support structure. The first layer of bridges must be printed in low material flow. Basically, the bridge is the spot of a 3D printer where there is no connection with the other area. On 3D printers, a base layer is printed first, forming an object layer-by-layer. Bridging does not involve the base layer between two spots.

Decrease Temperature

If you are printing bridges and overhangs, be sure that the cooling fan on the part is at its highest level. In general, you should keep the print temperature as low as possible while building bridges and overhangs.

 When building bridges at low printing temperature settings, the filament will drop in the melting masses. Lowering it will allow the printer to extrude a consistent stream of filament and produce good-looking bridges.

The next tip is almost the same as the previous one. If your nozzle temperature is too high and too much filament is allowed to flow from it, the printing material will not have enough time to cool and set. This will result in filament sticking to your nozzle or forming a messy bridge.

A temperature tower is a great way to test how your printer handles different temperatures. To print one, you’ll need to manipulate the G-code so the temperature changes with each level. The Gcode is the file format understood by most 3D printers. Whether you are using the best 3D printer under 500 or large format machine, this is the file format to use. To get to this option in Cura, Select Extensions > Post-processing > Modify G-code, and add the “Vary Temp With Height” plug-in. 

From here, you can input the height increment for how you want to change or increase the temperature (in what quantity you wish to change it).

Decrease Print Speed

High 3d printing speed can also affect bridge quality. If your nozzle is moving too fast, the filament will not have time to adhere to the previous layer or set in time to bridge a gap. In other words, high print speeds can result in huge messes.

Try decreasing your print speed in 10-mm/s increments until you see some improvement. Don’t go too slow, though. If your nozzle moves too slowly, the filament will be suspended in the air for too long and eventually droops. So, play around with some speeds, and you’re bound to find the perfect one.

Adjust Model Orientation

Many 3D print experts will frequently mention the rule of thumb of how long bridges without support can last, though that number may still change depending on filament types and the settings on your slicer. If you did not adhere to this rule, your overhangs or bridges might need fewer layers to print, which reduces the structural integrity, increasing the chances of your parts breaking apart in the vat of your resin.

If you’re completely tired of tweaking settings to get longer bridges, or you don’t have the time to start, try orienting your model to totally (or mostly) eliminate bridges in the model. Just remember the 45° rule: If an overhang is greater than 45°, you’ll have to consider supports.

Add Supports

White color 3D print supports. Image source: Geeetech

In 3D printing, bridging, a surface at 90°, is supported at either end and connects the two raised points. In the end, at least with bridges, there is no 3D printed support material removal that needs to be worried about. 

Speaking of supports, why not use them? Supports will eliminate your worries about messy bridges. Don’t forget to remove supports after printing. Some models make this removal process nearly impossible, or it’s tricky to do so without damaging the surface of your print. Sanding and other post-processing methods are your friends.

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