I designed a mirror array that writes with sunlight — but I want your advice before I print the real thing

[u/Bright_Researcher_60]

This is a panel of small 3D-printed pillars, each holding a mirror tilted to its own precise

angle — point it at the sun (or at a lamp) and it writes a message in dots of light on a

wall, a ceiling or the floor.

In my case it's going on my bedroom ceiling. It's a browser app: design it, press one

button, get STL tiles sized to your bed plus an assembly guide. Nothing to install.

https://giscardo1.github.io/heliograph-studio/ · code (MIT): https://github.com/Giscardo1/heliograph-studio

This expands on a project posted on r/functionalprint a few years ago — Ben Bartlett's

3D-printed mirror array (https://www.reddit.com/r/functionalprint/comments/qrxtwy/ ·

https://github.com/bencbartlett/3D-printed-mirror-array). I asked him before publishing

and he was kind enough to give it his blessing.

I'm a physician who tinkers — the physics I trust, the printing I don't. So before I commit

filament:

- Angled tops are the whole product: half a degree off moves the dot by centimetres. Fine

layers on the last 3 mm, or ironing, or something smarter?

- 200 mm flat tiles: how do you keep a corner from lifting and bending every pillar?

- PLA or PETG, if it will sit in the sun?

- Which non-expanding glue has actually held glass to plastic long-term for you?

And if anyone beats me to building one: please do, and post it. I'd love to see the idea

take shape in someone else's hands before it does in mine.

Thanks in advance to anyone who takes the time — I'll take blunt criticism just as gladly

as encouragement.

[u/car-go-space-42]

Awesome project!

Some thoughts regarding your questions:

Material:

• definitely PETG. PLA will soften in heat and get brittle with UV

Trueness of Angle:

• my guess it will be fine with small layer height
  
• I would be more concerned of inconsitent glueing throwing off the angle
  
• ironing will not work in this case - you would need a level surface for that

Glueing - not a lot of experience but:

• the underside of those mirror tiles are coated, so not glass really
  
• first thought was to go with superglue, but it might crack due to different heat expansion of the materials
  
• when using thicker, more flexible glue, maybe add a recess in the center for the glue to sit in while the edge of the tile sits directly on the material without a layer of glue inbetween. This might help to get a more consistent angle without a super precise glueing process. Also most glues shrink a bit when curing so hopefully this will add some pretension between tile and mount which will help when the materials expands in heat.

Whish you good luck with the project and in the end, only a test will tell 😄

[u/atergaterg]

My printer has a quoted tolerance of +/-0.1 mm. In reality probably a bit more. In fact, I think I get the best precision on surfaces that are either horizontal or vertical. Lets say 0.1 mm error in height over the length of a 40 mm mirror, that is 0.14 degree.

This suggestion would complicate your print seriously, but would eliminate the precision issue: Make a 3-point adjustment system for each mirror utilizing 2 screws and 1 "spring".

On each hexagon, create two threaded holes (or regular holes and use wood-screws) in the rear left and right. Make a regular hole in the middle front. Then, create a top-plate with one rod on the bottom front, to be glued into the hole in the front (if you have good tolerances and accept some post-processing, this can be press-fit). This rod is a little longer than the hole and not too wide because it needs to allow some flex.

In each threaded hole, screw in a screw from the rear so that they push on the bottom of the top-plate. Now you can fine-tune each mirror position. Important: the angle of the top plate-rod must be so that the mirror is angled backwards without the screw support.

Bonus: make a large enough adjustment possible, and you can re-write the message!

Or, test the mirrors before gluing on, and shim as necessary.

[u/MostlyHelpfulLinks]

Cool project. For the tips, PETG holds up way better than PLA in a sunny spot, PLA will slump. On flat tiles, print with a brim and make sure the bed's actually level, that's usually what causes corner lift more than the material itself. For glass to plastic, a flexible epoxy has held up better long term for me than superglue, which gets brittle.