PVA-free dual extrusion backing

If you have an FDM printer that has multiple hotends or can otherwise switch between different filaments, you've probably thought about using the ability to create dedicated support hardware. Historically, the filament of choice for this has been PVA, as it can be dissolved in water after the print is complete. But if you've used it before, you'll know it's not without its own challenges. Luckily there may be an alternative - [ModBot] had heard that it was possible to use PLA to support PETG and vice versa, so he decided to give it a try. You can see how it works in the video below.

Of course you can just use PLA to support PLA and PETG to support PETG. However, depending on the supports and slicer settings, it may be difficult to remove the support after a clean print. Slicers have made major improvements in this area, but it's still not ideal. Some use HIPS as a carrier, but this requires a solvent to dissolve and is also a bit exotic compared to PLA and PETG.

To illustrate, [ModBot] printed a few test items with the alternate media and made more reference prints using the same material with different settings. Typical use of gap slicers is 0.2mm, but when using different materials you can set the gap to zero. For the reference parts, he set the gap to zero and 0.1mm, both closer than you would normally print.

The PLA-only prints were essentially impossible to separate. While the PETG prints separated with tools, the resulting surfaces were ugly, with support residue and scarring. But prints with two materials and zero gap separated easily without tools and left a nice surface underneath.

If you have the ability to do dual extrusion, this could be a great trick to have in your toolbox. Certainly PVA will still be attractive if you have a support buried deep within a structure where it is physically difficult to access. Water can go where tweezers can't. But to support large accessible areas, this seems to be a game changer.

Sometimes auto supports can use a little help. There are plenty of supports and best practices for supports if you want to refine your process.