Intro:

The goal of this project was to see if it was possible to create a 3D printed magnifying glass with no sanding or polishing needed.

To get started you will need:

Access to a SLA type (resin) 3D printer (Ex: Form1+ by Formlabs)
Clear resin
A 3D model of a magnifying glass (Ex: http://www.thingiverse.com/thing:1006913)
Rust-Oleum Crystal Clear Enamel
Optional:

Step 1: Download STL Model and Print

You can download the STL model of the magnifying glass I designed from thingiverse.

http://www.thingiverse.com/thing:1006913

Or you can use your own design. Open the file in your 3D printing software and print out a copy. Since I have a Form1+ from Formlabs I used Preform as the software to print this model. I printed this model at .05mm layer height. Tip: The finer the layer height the less coats of enamel you will need to achieve the same clarity.

Step 2: Clean and Remove Supports From Your Print

Ensure your 3D print is free from uncured resin. You can do this by swashing your print in alcohol. I have had great success in removing uncured resin by using an ultrasonic cleaner filled with +90% isopropyl alcohol. This will leave your print surface smooth and dry (no longer sticky). If you don't have access to an ultrasonic cleaner you can cure resin by exposing your 3D print to UV light (sunlight) for a short time. Do not over expose your print to UV light or your print will discolor and deteriorate. Once your 3D print is clean, go ahead and remove supports. Be careful not to cut your self. I like to use special gloves when removing supports with sharp tools.

Step 3: Spray on Crystal Clear Enamel

Shake your can of Crystal Clear Enamel for a good while (3-5 mins). Allow the can to rest for another (3-5 mins). This will ensure your can is evenly mixed but not too agitated to introduce air bubbles on your print.

Lightly spray an even coat on one side of the print and then on the back side of the print. Always keep the can moving and never over spray. If you spray enough enamel that you see drippings, you are over spraying. After you spray if you see a bumpy surface you are either under spraying or you are spraying too far away from the surface (the enamel is semi dried and is loosely adhered to the surface). The surface of the print after a layer of enamel should be even, smooth, and consistent. Do not worry that the surface is milky or cloudy. The enamel will dry to a clear finish once fully dried.

Wait 20 min to 1 hour in between coats. Always hang dry the lens. Even if the surface of the print is dry to the touch, chances are the inner layers are still soft, so don't touch or apply any pressure to the print or you will permanently ruin the enamel coat. Spray enough coats until the surface of the print is smooth and optically clear. Hang dry for about 8 - 12 hours after your last coat.

In case of a mistake:

Accidents happen, it's okay. If your enamel coat becomes contaminated or uneven. Allow the layer to dry completely. Remove any contaminates or unevenness by wet sanding away using very fine sand paper (ex: 2000 grit). Clean the surface with distilled water and air dry or use a lint free wipe. Once dried, begin to spray enamel coats again until the surface is smooth.

Step 4: Magnifying Glass Is Finished

The concept works! Now its your turn to refine this and improve upon the process. What exciting developments await 3D printed optics?

Above and beyond experiment:

A future experiment will be to spin the lens at a high RPM and apply a coating at the center of the lens. The rotation of the lens should evenly distribute the coating on the surface reducing any distortions or unevenness.

Here is a video of the 3D Printed Magnifying Glass burning a leaf. Don't try this at home, kids.

https://www.youtube.com/watch?v=x3NXvE6GcOU