Since mid October of 2020, I’ve been slowly working towards a very specific goal – making FDM printed stone surfaces (specifically Dragon’s Quest tiles, designed by Ian Maclachlan) look great. More detailed “side quests” in the process include :
- Making the tiles look so good they don’t clash with the rest of the set, like walls and furnishings, which I’ll be printing mostly in resin instead of FDM.
- Effectively eliminating layer lines. Partly so it keeps up with the resin in terms of visual quality, but also to open up a much wider variety of finishing options. Techniques like dry brushing and washes are much less useful on curvy irregular FDM printed surfaces unless you want quite noticeable layer lines.
- Turn this into a reasonably efficient process. Slower printing isn’t a big problem, but one full set of tiles is around 9 or 10 square feet. If smoothing them out requires a lot of hands on time before painting, that could become prohibitive.
Note that this is not a general how to for better looking FDM prints. I’m focusing on quality of “top” surfaces, i.e. models like tiles intended to print flat on the bed, with irregular peaks, valleys, curves, and similar details. These are nearly impossible to print with FDM without leaving noticeable artifacts, especially layer lines.
So far, my search for smooth stone has focused on two areas
- Optimizing slicer profile settings to get near maximum possibly quality – with a clear priority of quality over print speed
- Techniques to further cleanup and smooth the prints prior to painting
I’ll be writing up more details, but the short version is after testing many different combinations of slicer settings, I’ve got something that works but still may have room for improvement. Here’s just one of the earlier sets of test tiles
Smooth as a baby’s – oh wait, can’t use that any more…
Early in the process, Ian suggested trying PVA glue to fill in the layer lines. Tried some good ol’ Elmer’s School Glue. It helped some, but wasn’t super impressive. PVA tends to shrink as it dries, so it took a lot of coats before layer lines started disappearing. Did a bit of Googling and decided to thicken it up a bit by adding cornstarch. Seemed to fill in quicker (fewer coats), but it also seemed like a weaker bond which might be prone to flaking off.
I switched to a thicker PVA – Titebond II Premium wood glue, and things improved. The next thing I wanted to dry was adding talc powder – which USED to be widely available as the main ingredient in most “Baby Powder”. Until it was determined that talc powder could cause respiratory issues, and talc stop being used in baby powder. The only locally available source I found was Gold Bond medicated powder – which appears to be mostly talc powder, but has other stuff that may or may not help. But it seemed worth a try, and I saw some promising results – enough to order some “pure” talc powder.
Current tests are a mix of 4:1 mix by weight of glue to talc. It’s taking around three coats before the layer lines are gone.