What Would Sherlock Print, If Sherlock Printed In SLA Resin?

Resin printing — or more appropriately, stereolithography apparatus printing — is a costly but cool 3D printing process. [Evan] from [Model3D] wondered if it was possible to produce a proper magnifying glass using SLA printing and — well — take a gander at the result.

A quick modeling session in Fusion 360 with the help of his friend, [SPANNERHANDS 3D Printing] and it was off to the printer. Unfortunately, [Evan] learned a little late that his export settings could have been set to a higher poly count — the resultant print looked a little rough — but the lens would have needed to be sanded anyway. Lucky coincidence! After an eight hour print on his Peopoly Moai using clear SLA resin, [Evan] set to work sanding.

Over several hours, [Evan] hand polished the lens, steadily working his way from a heavy, low-hundreds  grit sandpaper, all the way up to 3000 grit! A little time on the polishing wheel using 3.5 and 1.2 micron polishing paste to “buff the hell out of it” turned out a fine looking-lens.

[Evan]’s only gripes about the project are the slight yellowing of the lens — which he says could have been from over-curing, or a property of the resin he used — and needing a little more time on the buffing wheel. That said, we suspect his next attempt at making a lens will wind up in a laser engraver.

17 thoughts on “What Would Sherlock Print, If Sherlock Printed In SLA Resin?

  1. According to the American Optometry Assoc, it’s illegal to make a lens to three figure diopter precision. They alone are entitled to do such. Raspberry! Things will change.
    Actually lens grinding is a fairly simple geometric machine thing. They just set a dial and grind away your prescription.

    1. Three figure precision is not quite in order here is it? I mean that’s some very precise stuff if I’m not mistaken.
      And in that sense I expect it’s about claiming you make medical/science-instrument grade lenses when you can’t that would be barred, if anything.

  2. I am wondering what measure should one take to properly protect itself from the fine particles this process produces. I do not consider this any different from any material fine grinding, polishing, just would like be more informed.

  3. I do Fresnel, simplex, coplanar lenses with my Form 2, even laser chambers using the mercury-as-mirror trick. It is so much fun. Especially, the dielectric constant from the Formlabs resin is quite consistent in all the tanks I bought.
    Sanding is important, but if you use a power rotary tool, you can easily create too much friction heat/static electricity and radicalise the surface layers (i.e. burn the resin). This will result in deep yellowing similar to too long UV exposure. In my experience, this was the biggest source of yellowing, since the Form2 resins UV protective dye works to protect the inner layers very well up to several hours, and any UV damage that remains on the surface can be easily sanded off with 800 grit. In theory, you can use the acetone trick to correct the oxidation state of the polymer, but it doesn’t work that well for me.
    For me, the thing that works best is this workflow: 1-2 hours of UV cure at 405 nm led. 800 grit wet sanding, 1200 grit wet sending, hand applied acrylic repair kit to fill the microscopic gaps, (optional) car clear lack
    Please also check this out, where they recommend epoxy treatment

    1. The coating step reminds me of using cellophane tape to counteract fogged glass windows. Place the tape on the fogged side to fill the gaps in the surface and make it clear again.

    1. It would, in fact, be interesting to use this process to create an aspheric lens. Spherical lenses are used mainly because they are easy to grind; if you are going to 3D print the thing, it can be any shape. However, I do not know what curve a powerful lens “ought to” have to avoid spherical aberration.

  4. Rule 1: Don’t make a spherical lens using an ellipse drawing function. Rule 2: Don’t use the same wheel with different polishing compounds. Rule 3: No localized heating during polishing.

    Suggestions: Print a negative “tool” at the same time. Grind and polish using the mirror grinder’s pattern, alternating with the front and back of the lens against the tool. This will get rid of variations. Spherical lenses are not ideal, but a thin one works well. And the symmetry makes polishing with a tool work great.

    That reminds me of something. You could make precise flat surfaces. Take three latish objects, A, B, and C. Grind A against B, and B again C, then C against A. Repeat until smooth. They cancel each other’ bumps. Optical flats are made this way.

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