Ocarina of Time Coasters: Part Two

Click here for Part One: Modeling

Welcome back!  I'm slowly but surely making progress on these damn coasters, and am now at the stage where I need to give the originals a good finish so they'll actually make good-looking molds.  This should be a shorter post than the previous one, as the process isn't super exciting... except for maybe the parts of it I messed up, of course.

Part Two: Finishing My Originals

Due to the wonky ways I've been printing my parts, they don't exactly come off the printer looking fabulous.  In fact, the edges that touched the supports can get pretty jagged.  This is where my dear friends sandpaper and Dremel tool come into play.  Pardon the lack of pictures-- the sanding process makes an absolute mess, and I don't want to get plastic dust all over my shiny new phone.

To give a rough overview, I've been using a sanding drum of unknown/ very low grit on the Dremel to hack off the more jagged pieces.  After that, I had no problem scrubbing away with a sheet of 220 grit sandpaper attached to a foam sanding handle, which it came with in a small kit from the hardware store.  Once I can't feel any jagged pieces with my fingers, I've started giving it one more go-over with a wet/dry sanding block that I bought years ago to use on clay sculptures.  I have no idea what grit it is, but it's pretty fine even compared to the 220.  Iterations Three and Four have benefited the most from this mystery sanding block, as I can actually reach the inner surface of the coaster and sand it until it's nice and smooth.

Oh, something important I learned!  Don't rely on your eyes when trying to sand 3D prints, as the thin walls will let light through in some places but cast shadows in others.  This'll cause a lot of weird discrepancies between what the surface looks like and what the surface feels like.  I thought I had a big gouge in the middle of my Forest Medallion print, but it turned out to just be a thin part on the backside of the wall.

Now, as to the matter of the prints I ruined...

Ugh, this again?

So while I was getting started in home printing, I came across a neat product by Smooth-On that's meant specifically for smoothing out 3D prints.  It's called XTC-3D and is a gooey resin that's supposed to self-level after you brush it onto your prints.  Although it's a really nifty product that can turn a crummy print into a smooth, shiny print, I've had mixed results in my attempt to use it.  Most of my applications have at best still been kinda bumpy, at worst... well, again, the lumpy mess you see above.  Smooth-On recommends working at room temperature, which I'm willing to bet is causing my issues-- I'm working outside in the Arizona desert, where it's still getting up to 100F during the day while most people are enjoying cool autumn weather right now.  Since exposing a heat-curing plastic to heat makes it cure faster, my working time decreases faster than I can work when I try to finish a large batch of prints.  I'm pretty sure that's where I slipped up with Iteration Two.  I went back to do a second application and smooth things out a bit more after coating all six coasters, and by then the resin was starting to set up.  If I had left them alone, they probably would have just been a little bumpy like the time before.

On a related note, if you decide to use this product on your own prints, resist the urge to use cheap chip brushes.  Seriously, they've caused me so much grief that I kick myself every time I use one instead of throwing them out and getting foam brushes instead.  XTC-3D is a little tacky, and gets increasingly more tacky as it starts to cure.  Tacky plus cheap brush equals so many bristles getting pulled out and stuck to the resin!  Ahem.  Naturally, this causes you to either end up with bristles stuck in your print, or take the time to pull each one out and redo the section of resin you just screwed up by digging it out.  In my case, you're likely to have both occur and get really mad at yourself for being dumb.

At this point, I'm hoping sanding alone will suffice for Iteration Four.  However, gluing the two pieces together has left a small gap around the inner edge of the Forest Medallion prototype, which showed up as a thin rim sticking out of my new test mold.  I trimmed it as best I could, but my X-Acto knife didn't exactly slice the rubber too well, so it ended up looking sloppy.  If it shows up in the final cast and can't just be filled in with some sealant spray, I'll have to give XTC-3D another shot.  I'll be sure to post an update if that happens.  Until then, may the super glue be with you, not on you!


UPDATE 10 October: After the above-mentioned mold was used, I've discovered that whatever grit my wet/dry sanding block just doesn't cut it for mold-making-- I was left with obvious layer lines in the mold and test cast even though my fingertip couldn't feel them.  After a bit of Googling, I've found people recommend getting up to 1500+ grit, so I bought a variety pack of wet/dry sandpaper sheets.  My current plan is to do a coat of XTC-3D and follow it up with a good sanding from each grit of sandpaper I got-- if I still can't get a good mold, I'll be sure to come back and update this page again.