This is a reformatted version of my post on reddit
I recently got a roll of Polycast SP801C, which is a variant of the polysmooth resin(PVB), but it is tailored for investment casting metal parts. The special thing about this filament is it prints as easy as PLA, burns out clean(testing soon), and most of all, it can be smoothed/ dissolved with alcohol. I have also noticed that it cuts and sands like ABS, which is a nice change from PLA.
I have been printing and smoothing the SP801C with good results so far.
The diameter measured 1.75mm exact and is very circular(better than can be measured with calipers)
The printing characteristics are great, nearly identical to PLA with very minor stringing, but excellent bridging, and support structure breaks away perfectly.
I had some trouble with bed adhesion on glass coated with Mod Podge (PVA glue) at 45C but increasing the temperature to 60C with a 10mm brim, or 75C without a brim solved it for me. I've been running the hotend at 215C for the first layer and 205C for the print. My printer has a large 0.8mm e3D V6 nozzle because I typically print big and fast for functional parts, where layer lines aren't important; for the fine stuff, I switch back to the 0.4mm nozzle.
I have tried smoothing the Polycast by putting the parts in a ziplock bag with a couple ml of isopropyl alcohol(IPA). I Inflate and seal the bag, then shake for about 10 minutes, until the parts look smooth. I let the parts dry on a piece of wire mesh for easy removal once hardened. This approach is a bit ham handed and Iv'e had IPA leak in to the model through an eroded gap and cause a temporary squishy spot. To be fair, my method probably erodes the model more than the official "polysher" would.
On beefy 0.4mm layers it significantly reduces the layer lines, but they are still present as very shallow and gradual undulations. The surface has a nice high gloss, and scraping my fingernail over the layers does not produce the typical "zipp" noise of a normal print. Although it is not completely aesthetically smooth, this partial smoothing should be beneficial for the casting process, removing all of the sharp creases that normal layer lines have, which should reduce damage to the investment material, reducing inclusions in the castings.
On normal 0.2mm layers the smoothing works completely, the layers merge into a smooth glossy surface.
Benchy Smoothed print defects still show, but the surface is smooth
3D scan bust smoothed
Sprue tree smoothed
Sprue tree closeup
One additional benefit of the SP801C is being able to use IPA to solvent bond custom 3D printed sprues to the models. I printed some custom sprues that position the model accurately within the confined space available in the investment flask, and also form the pouring funnel after the plastic is burned out of the investment. Being able to print the sprues separately from the models allows each to be printed in their best orientation, sometimes eliminating the need for support.
Sprue tree assembly
I am hoping to Invest the parts this week, and burn-out then cast this weekend. I will provide another update after casting.
Sprue tree and 3D scan next to flasks