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09-17-2017, 10:00 PM
(This post was last modified: 09-18-2017, 12:46 AM by Dyne.
Edit Reason: Additional pics, rearrange text
)
So, the test mold and mother mold are done. I knew before pouring any resin that the silicone mold had defects due to trapped air, but I was curious how it would turn out, so I cast a test part last night anyway.
The resin I'm using is Famowood Glaze Coat; the kind of stuff you use for covering bartops and tables in a thick gloss coat. It's a bit cheaper per unit than Alumilite's Amazing Clear Cast Resin. The Famowood resin has pretty low viscosity, so it pours easily. The stuff says final cure takes about 72 hours, but I wasn't going to wait that long for a test part with known defects. After 15+ hours it wasn't *quite* fully cured -- the edges were slightly tacky -- but it was reasonably solid, so I went ahead and demolded it. (As of 25 hours, it has lost most of the tackiness.)
An aside:
During the same resin pour, I used a Yaley cabochon mold to cast a (clear) BB-8 holoprojector lens. The mold I have is the 4x4, 1 inch diameter version rather than the 5x5, 3/4 inch that is usually used (because the latter wasn't in stock), so I marked a well to ~3/4 inch diameter and only filled it to that point. That makes my lens a spherical cap rather than a true hemisphere, but I can live with that until I get my hands on the proper mold.
I could've just ordered a lens from the club, but the thread I've been watching promised additional colors "soon". That was months and months ago, and as far as I know they've never actually been made available. Since I was already going to be doing Treadwell lenses, I decided I could just make my own. Currenty I have red dye and need to grab some yellow to get an orange lens like I want ... but I really want to try mixing in fluorescent highlighter dye and illuminating with a UV LED.
![[Image: normal_20170918_005333-smaller.jpg]](http://www.rebeldroids.net/gallery/albums/userpics/10380/normal_20170918_005333-smaller.jpg)
As expected, the Yaley mold pretty much produced a perfect lens, so I know this resin is capable of the clarity I'd like to achieve.
The thin rim of the BB-8 lens was a bit flexible after demolding at 15 hours, but the pour was also somewhat larger than 3/4 inches in diameter due to surface tension and such, so the rim will be sanded down anyway. There was no tackiness on this piece; presumably it cured a bit faster due to the smaller size.
Back to the treadwell lens:
My test part came out pretty easily. Since the planar surface of the lens was just open liquid resin during the pour, that came out very smooth and shiny, just a few small defects due to bubbles on the surface that I forgot to deal with. Indeed, it is so smooth that it reflects everything on the convex surface at certain angles.
As predicted, there were fairly large flaws on the convex surface -- mostly protrusions caused by air trapped when making the silicone mold. The silicone also captured some layer lines (more than were readily apparent on the master), but these aren't easy to see from straight on and mostly just serve to make it a bit like a fresnel lens. I got some filler primer and some finer grit sandpaper and improved the surface of the master considerably after this cast.
There is some fogging in a few places on the cast that I can't account for. I don't think it was improper mixing; this stuff is supposed to be mixed in two different containers for a total of twelve minutes, so it's pretty thoroughly stirred up. Maybe it was plaster dust contaminating the silicone mold, thereby getting embedded in the resin.
![[Image: normal_20170917_204425-cropped.jpg]](http://www.rebeldroids.net/gallery/albums/userpics/10380/normal_20170917_204425-cropped.jpg)
![[Image: normal_20170918_013912-cropped.jpg]](http://www.rebeldroids.net/gallery/albums/userpics/10380/normal_20170918_013912-cropped.jpg)
Aside from the obvious flaws, the lens has decent clarity and actually does work reasonably well as a magnifier. Since the basic lens form is mostly there, it conceivably could be sanded and polished into something usable. I could even print a matching concave tool to help with this. This would probably be a lot more effort than just trying for a better mold, so I'm doing that instead. Edit: Actually, it was fairly easy to get it looking kind of like a "weathered" lens. It's slightly frosted (too many Tatooine sandstorms?) and still has a few remnants of the defects (small flying debris?).
What, you think Treadwell is like some fancy-schmancy BB droid, straight off the factory floor with super clear lenses? No sir!
![[Image: normal_20170918_035832-smaller.jpg]](http://www.rebeldroids.net/gallery/albums/userpics/10380/normal_20170918_035832-smaller.jpg)
![[Image: normal_20170918_040203-smaller.jpg]](http://www.rebeldroids.net/gallery/albums/userpics/10380/normal_20170918_040203-smaller.jpg)
This was achieved simply by wet sanding from 120 > 220 > 800 > 2000 grit, and then waxing it a few times with turtle wax. If I get my hands on some finer sandpaper or polishing compound, I could probably get it less frosted without much trouble.
A new mold has been curing for the last few hours. I started with a thinner initial layer of silicone this time, and made more of an effort to work air/moisture out from beneath it. We'll see how that goes.
The resin I'm using is Famowood Glaze Coat; the kind of stuff you use for covering bartops and tables in a thick gloss coat. It's a bit cheaper per unit than Alumilite's Amazing Clear Cast Resin. The Famowood resin has pretty low viscosity, so it pours easily. The stuff says final cure takes about 72 hours, but I wasn't going to wait that long for a test part with known defects. After 15+ hours it wasn't *quite* fully cured -- the edges were slightly tacky -- but it was reasonably solid, so I went ahead and demolded it. (As of 25 hours, it has lost most of the tackiness.)
An aside:
During the same resin pour, I used a Yaley cabochon mold to cast a (clear) BB-8 holoprojector lens. The mold I have is the 4x4, 1 inch diameter version rather than the 5x5, 3/4 inch that is usually used (because the latter wasn't in stock), so I marked a well to ~3/4 inch diameter and only filled it to that point. That makes my lens a spherical cap rather than a true hemisphere, but I can live with that until I get my hands on the proper mold.
I could've just ordered a lens from the club, but the thread I've been watching promised additional colors "soon". That was months and months ago, and as far as I know they've never actually been made available. Since I was already going to be doing Treadwell lenses, I decided I could just make my own. Currenty I have red dye and need to grab some yellow to get an orange lens like I want ... but I really want to try mixing in fluorescent highlighter dye and illuminating with a UV LED.
As expected, the Yaley mold pretty much produced a perfect lens, so I know this resin is capable of the clarity I'd like to achieve.
The thin rim of the BB-8 lens was a bit flexible after demolding at 15 hours, but the pour was also somewhat larger than 3/4 inches in diameter due to surface tension and such, so the rim will be sanded down anyway. There was no tackiness on this piece; presumably it cured a bit faster due to the smaller size.
Back to the treadwell lens:
My test part came out pretty easily. Since the planar surface of the lens was just open liquid resin during the pour, that came out very smooth and shiny, just a few small defects due to bubbles on the surface that I forgot to deal with. Indeed, it is so smooth that it reflects everything on the convex surface at certain angles.
As predicted, there were fairly large flaws on the convex surface -- mostly protrusions caused by air trapped when making the silicone mold. The silicone also captured some layer lines (more than were readily apparent on the master), but these aren't easy to see from straight on and mostly just serve to make it a bit like a fresnel lens. I got some filler primer and some finer grit sandpaper and improved the surface of the master considerably after this cast.
There is some fogging in a few places on the cast that I can't account for. I don't think it was improper mixing; this stuff is supposed to be mixed in two different containers for a total of twelve minutes, so it's pretty thoroughly stirred up. Maybe it was plaster dust contaminating the silicone mold, thereby getting embedded in the resin.
Aside from the obvious flaws, the lens has decent clarity and actually does work reasonably well as a magnifier. Since the basic lens form is mostly there, it conceivably could be sanded and polished into something usable. I could even print a matching concave tool to help with this. This would probably be a lot more effort than just trying for a better mold, so I'm doing that instead. Edit: Actually, it was fairly easy to get it looking kind of like a "weathered" lens. It's slightly frosted (too many Tatooine sandstorms?) and still has a few remnants of the defects (small flying debris?).
What, you think Treadwell is like some fancy-schmancy BB droid, straight off the factory floor with super clear lenses? No sir!
This was achieved simply by wet sanding from 120 > 220 > 800 > 2000 grit, and then waxing it a few times with turtle wax. If I get my hands on some finer sandpaper or polishing compound, I could probably get it less frosted without much trouble.
A new mold has been curing for the last few hours. I started with a thinner initial layer of silicone this time, and made more of an effort to work air/moisture out from beneath it. We'll see how that goes.