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I am searching for some material, that can be turned (even with post-processing) into a "glass" like texture.

Additionally, it should withstand some pressure (0.5 MPa in approximately 30 mm diameter canals) so PLA does not fit my case... Mostly, I would appreciate some CFR, since its mechanical properties are amazing, but it doesn't have to be that way.

I own Markforged FX20, Mark two and Ultimaker S5.

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  • $\begingroup$ Could we please have some more information regarding the finished product that you have at the end of this process. For example, are you going to produce a viewing window to be included as a component of some other practical part? $\endgroup$ Feb 10 at 15:32

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Print problems

Only very few FDM materials are truly transparent. When printing a line next to line, inclusions of air can and will create outer boundaries that would be visible, so it is paramount to print in such a fashion that prints are as tight as possible. Another problem is, that under normal conditions the extrusion-extrusion boundaries are quite visible and that have different refraction indices inside the part. To remove those boundaries and gaps, it needs special printing parameters that result not only in filling every gap but also partially melt all adjacent lines to create a truly solid part. As such, FDM prints with multiple layers for walls are extremely hard to make fully transparent.

With extreme tuning, the internal voids can be reduced to almost none or truly none, and inter-wall bonding increased to be nigh invisible, but this leaves outer walls.

Extreme settings for clarity

Stefan from CNC-Kitchen had a whole talk about these specialty print parameters with which he achieved very low-opacity prints in some, but not always all directions. As a baseline, he used settings proposed by Rygar1432. He started using a very transparent PCTG, with already very good results, and then experimented with PETG, which had a slightly less transparent look to it after optimizing the settings.

Comparison shot of PCTG and PETG print with best settings

The exact composition of the print material was found to have tremendous effects on the transparency, thus different manufacturers and even rolls from different batches might behave differently and require different settings. Further, some filaments absorb moisture over time, which will degrade the print result by creating voids of entrapped water vapor. As printers also heat slightly differently due to the variance of the heater cartridges' resistance, your settings might not be perfectly applicable to another printer of the same type and might require adjustment. The most important basic settings discussed were:

  • extrusion width & layer height
    • Compared to the standard 0.4 mm or 0.45 mm, a wider extrusion of 0.5 mm was used, but the layer height was significantly reduced to 0.12 mm at the same time, resulting in the plastic getting pressed tighter against the previous print and allowing fusion to other walls
  • perimeters
    • Using only a single outer perimeter made the print mainly composed of infill and reduced the different geometries that could create pockets
  • printing speed & part cooling.
    • Compared to classic prints, the printing speeds had to go way down to 15 mm/s, which is about 1/4 of typical print speeds. The slower print speed assists with keeping the extruded plastic hotter in the area of the nozzle, assisting with inter-extrusion bonding. This was further assisted by disabling part cooling. However, this resulted in very bad results of bridging material.
  • Infill Geometry
    • An aligned rectilinear infill pattern was necessary to remove almost all voids, which was coupled with no top and bottom surfaces to again, reduce different print geometries that could create voids in the print.

comparison between aligned and classic rectilinear patterns

The most important factor was the extrusion multiplier, which for Stefan's machine was best at about 101 %, as above that he started to experience some deformation of the part's outer shape, mostly in the shape of rough surfaces.

row of prints with increasing flow multiplier, 101 % demarked

A slight bit of polishing and cleanup was at times required, as Stefan retold. Also, again, the outer perimeter clearly shows in different alignments of the print, best shown with this shot. While you can see almost undisturbed through the part down like, sideways the outer perimeters are very opaque.

Alignment effect on print clarity

All in all, you could get a very well-transparent print in some directions, but the outer surfaces are always somewhat rough.

Specialty Filaments

Some filaments can be treated after printing to create a single, well-fused outer surface that is nigh fully transparent. This precludes prints with many walls unless the interior is already clear, but the results are known to be stunning for prints with a single or few walls. Do note that the order of filaments mentioned here is by the toxicity of their solvents, so the higher up in the list, the less dangerous it is.

PVB

The Hourglass by Mageb uses a chemical quirk of polyvinyl butyral (PVB): it is soluble in isopropyl alcohol to a good degree, resulting in softening and smoothening of the surface if the right exposure time is used. It's hard to predict if and where the IPA can creep into the walls to remove cavities without destroying the print's shape, so this effect is generally best used on Vase-mode prints. This of course limits the wall thickness and strength of the print.

ABS

It's well known that Acrylonitrile butadiene styrene (ABS) dissolves in Acetone. In a similar fashion to PVB, Acetone liquid or vapors thus can be used to smooth out the outer deformities of a print and create a smooth surface, though not only is Acetone much more dangerous than Isopropanol due to toxicity, ABS itself is a more challenging printing material to PVB and can emit some dangerous fumes in printing. Since ABS has lost ist appeal to most hobbyists, I could not find any report on possible clouding issues from the treatment.

PETG

Yes, Polyethylene terephthalate glycol-modified [copolymer] PETG is chemically smoothable. However, the chemicals that can dissolve PETG are even more toxic than for ABS: Dichloromethane, methyl ethyl ketone (MEK), toluene, and cyclohexanone are extremely toxic and nobody would guarantee you that the print will stay clear and that the prints won't cloud from the chemicals penetrating the print.

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To be honest,3D printing has a poor reputation when it comes to transparent parts as resin tends to discolor when exposed to UV light, and need to be coated with another material such as a clearcoat in order to maintain their glass like finish for any time.

Filament is even worse, it yellows quickly and will have visible layer lines no matter how much you tune your printer.

With machines of the quality that you're mentioning, you would be best going with the manufacturer's own brand PETG, turning the extrusion up to the maximum and the cooling off, then the speed down. Ironically, thicker layers are best as they bond together better and so form less pronounced layer lines.

My personal recommendation would be use your printer to create a part in an opaque material, and then use that part to create a mold so that you can create your part out of two part epoxy resin, or create a blank that can be used in a vacuum former.

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