Dyne's Treadwell

[kresty]

Wow, that sounds like something I'd do (Actually I did it a little in a different axis, but caught myself).

Glad you got it figured out!

[Dyne]

Thanks, I've been printing almost non stop since I got it fixed (most recently, wheels that don't wobble for Artie's drive)

I've got both lens retainers printed now, my lens positive master is sanded and waxed, and I got some supplies to attempt a basic mold and resin cast.

I'm tempering my expectations. My research has led me to believe that to get a proper clear lens I would need both a vacuum chamber (to degas the silicone) and possibly a pressure chamber (to pressurize the resin). Probably better silicone, too (I'm using the cheapo method of 100% silicone caulk).

[savagecreature]

Thanks, I've been printing almost non stop since I got it fixed (most recently, wheels that don't wobble for Artie's drive)

I've got both lens retainers printed now, my lens positive master is sanded and waxed, and I got some supplies to attempt a basic mold and resin cast.

I'm tempering my expectations.  My research has led me to believe that to get a proper clear lens I would need both a vacuum chamber (to degas the silicone) and possibly a pressure chamber (to pressurize the resin).  Probably better silicone, too (I'm using the cheapo method of 100% silicone caulk).

I've done human head casts with silicone caulk. It's capable of capturing quite a bit of detail and doing a damn good job in general if it's done right. I look forward to seeing your results.

[Dyne]

Hopefully it doesn't capture too much detail.  

Had a bit of a delay due to automotive issues yesterday (I think my headlight switch died or got knocked loose while I was replacing a fuse; I currently only have lights when I hold the high beam lever), so I just molded the silicone on the master a little while ago.  I made a mold box as I'm planning to pour a plaster mother mold tomorrow after this cures, to keep the silicone mold from deforming while casting the resin.  It's ugly, but hopefully it works.

Silicone Lens Mold

[Dyne]

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.

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.

[savagecreature]

that's pretty darn cool, even with the frosted look. Nice work.

[Dyne]

Thanks.  I actually improved the clarity a little bit after I last edited the post, because I was reminded that toothpaste is mildly abrasive.

Today I pulled off the new silicone mold.  Overall it came out smoother.  There are still blemishes, but nothing as large as before, and there are no layer lines, so parts cast with this should require less cleanup and trimming.  Not that it'll help much; any sanding will bring the native clarity down to match the existing lens, so my goal is a mold that doesn't require sanding the lens surface at all, at least until I can get something that will improve on what I've got with the existing lens.

A new wrinkle is that the second mold lifted some flakes of primer off the master; I stupidly forgot I'd need to seal the thing.  Since these are experiments, I decided to go ahead and cast a second lens in the new mold without making a mother mold.

I also attempted my previously-described experiment with the highlighter dye.  The dye sometimes forms globules and swirls because it's got a fair amount of water in it, and water also likes to fog up some resins, so my experimental parts are unlikely to be perfectly clear.  

Wasn't sure how much resin I'd need to pour the entire Yaley mold, so I mixed extra.  Turns out I didn't need much.  I ended up with enough leftover resin with highlighter dye that I could pretty much pour a second Treadwell Lens in the original silicone mold.  So a UV reactive Treadwell lens is going to be a thing now.  

I'm trying to decide what color of blue Treadwell should be.  The native plastic of the relevant part of the Trident projector is a somewhat desaturated blue (lighter than the filament I'm using, which is Inland Egyptian Blue PLA):




This photo seems like it's the best guide.  It feels like they roughly color-matched the blue of the lens holders, maybe a touch darker/less saturation.  The base also appears slightly two-toned, inboard from the treads:


From what I can do in an image editor using the photo and a color sample thing on Sherwin-Williams site, the droid feels like something between SW 6530 (Revel Blue) and (SW 6531 Indigo). If anyone that has the original part wants to color match that to paint samples or pantone colors or some such, that could be useful. The Camera > Image file > Monitor chain is notoriously unreliable.

[savagecreature]

I have an original one here on my desk. Now I just have to figure out how to identify exactly what blue it is.

I'll see what I can come up with.

[Dyne]

No rush. I still have to finish designing the head before I can really think about painting, and the original part is just a similar reference point anyway; I'm pretty sure they didn't use it raw.

[Dyne]

Here are the results of the latest pour:

At nearly 24 hours, the actual Treadwell lens was demolded.  It came out a lot clearer than the previous attempt, but it still has blemishes here and there on the convex face, and everything in contact with the silicone is still sticky (as is the silicone mold).  I think my epoxy-hardener ratio was slightly off in this batch and it's taking longer to cure.  (Edit: After over 32 hours, it's still tacky, but slowly improving.)

Everything with the highlighter dye was exactly the opposite of the clear lens -- tacky on the planar face, thoroughly cured on the convex face.  These parts were also less rigid than I expected at this stage.  The BB-8 lenses were almost too flexible to demold, but I eventually got them all out intact.  The dyed Treadwell lens was demolded easily, but had the consistency of a mildly warmed jolly rancher.  I could've bent it entirely out of shape if I'd wanted to.  I'm putting it in a lens retainer and letting it cure further there to keep it in shape.  

Given that the tackiest part of the dyed Treadwell lens was a blemish on the planar face that released unmixed dye, my theory is that any highlighter dye near the surface is close enough to reach it before the resin sets, where the moisture tends to spread across the surface and affect curing.  That doesn't happen with the clear parts, nor does it happen on the lower, convex surfaces.

Regardless, I took photos of my mad science:

The lines in the Yaley mold are the marks I made to indicate 3/4 inch diameter, and you can see I still managed to pour most of these too large.  The non-glowing well on the upper right in the second photo is another clear BB-8 lens that I poured.  It works as a control, and has none of the tackiness of either the clear lens or the dyed lenses.  Just like the first clear BB-8 lens, it came out essentially perfect.

You can see in the UV photo that the dye didn't really mix evenly; there are little concentrations and cloudy areas here and there.  That's at least partly because I put the dye in last, after the regular mixing and pouring of the clear parts.  If I'd put it in early in the normal mix, it'd likely be more evenly distributed.  Under normal light, the dyed BB-8 lenses look like somewhat more transparent/more glossy/less frosted versions of the dyed Treadwell lens.

Anyway, the UV stuff is just for fun, and if nothing else, it serves as practice for anything I want to cast for Halloween.  And who knows?  Perhaps someone might want to make the BB-series equivalent of R3-B0017...