FDM Part Smoothing

When you are looking for a way to make very functional FDM parts look closer to being traditionally manufactured parts there are few methods out there. Some of these require manual working of the part, some mechanical, while others require almost no work at all.

One of the major concerns that comes up regularly is the dimensional stability of the parts after the finishing process. When tumbling parts or sanding them you are typically removing small amounts of material from the surfaces, especially the edges, and this can be an issue if not monitored carefully.

Another process that can smooth out parts is to coat the part with either an automotive body filler type substance (ideal for painting parts when dimensions are not critical) or using a two part epoxy type product to smooth and gloss a part over. Both of these methods work, but they are time consuming and will affect the dimensional accuracy of the part(s).

FDM Part Smoothing

The top lid of this box has not been smoothed or post-processed, while the rest of the body has been. The FDM stair stepping lines are clearly visible on the lid, but not on the body.

One of the fastest and most dimensionally accurate methods of smoothing ABS or ASA parts is to use a solvent like acetone. There are four methods of applying the solvent. One method that gives you the least control is to dip parts into liquid solvent. This method can be dangerous and cause pooling of solvent in areas of parts that can cause dimensional instability if not dealt with quickly. The other three methods give you a greater degree of control and these are brushing on solvent, airbrushing on solvent, and dipping parts into vaporized solvent. All but the latter can be accomplished with simple safety precautions like gloves, eye protection, and a respirator/hood vent.

The method of dipping parts into vaporized solvent does require specialized equipment that can create and contain the vapors during use, but this method does give a pretty high degree of control simply by adjusting the duration of the dip and the number of dips. Finally, these solvent-smoothing methods can be enhanced further by selectively spot sanding before or between applications.

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