Easy lithopanes with Simplify3D

[jimc]

I have been buying my lighting stuff for years from superbrightleds.com. A quick look on their website and youll see them there

[Tim]

I finally got around to writing the "lithosphere" generator. It will create lithophanes on spherically curved surfaces, with options for partial wraparound, holes at top and/or bottom, margins and top and/or bottom, etc. Assuming that it is given sane inputs and good support structures can be generated to hold it up while it's being built and keep the top from collapsing, then it should be good for creating custom night lights, Christmas tree ornaments, etc.

S3D does not play well with cylinders and spheres, even when it declares them to be manifold. It has the tendency to fill the center of the sphere instead of the walls on randomly selected layers. Not often, but enough to be an annoyance. Maybe I can convince the S3D people to fix their bug, but I'm not too hopeful. They seem to be about as responsive to bug reports as most purveyors of closed-source software. The last time I tried, they would not admit that they had a bug.

I have not yet posted this on Thingiverse. I usually want to have an example print to show, but I want to have it slice correctly before try to print something.

Michael globe

michael_globe.png (281.97 KiB) Viewed 11968 times

[Toby]

That is very cool. I'd like to try out your code but before I learn it I'd like to try and slice an example in S3D- do you have one you can post for me to play with? I might find a way to avoid some of the S3D glitches.

Also, I have this idea for a custom gcode generator that would be easiest to implement on sphere-like objects. What it would do is, the shallower the pitch of the model, the lower the layer height would get, enabling you go further and further without any support. My back-of-the-envelope calculation convinced me getting to within 10 degrees of the north pole is feasible, at which point you could just stop (like with a litho-light-shade) or bridge a platform and build from there if the object isn't too big.

I have the slicer part of it working, but haven't dived into the gcode generator. This would be good motivation to implement the thing.

[Tim]

Toby,

The files involved are large, so instead of trying to link it here, I just put it on my server,
and you can grab it from this URL:

http://opencircuitdesign.com/~tim/archi ... obe.stl.gz

(gzipped, it's 7.6MB). If you want any particular variation of it, let me know. This one is closed on top and open on the bottom. I don't try to flatten the bottom in the software; I was just relying on S3D to adjust the offset to give the bottom more surface area on the plate.

[Toby]

Got it. Unzipped it was over 50Meg- I assume that's the ASCII stl format at work.

In any case it really wasn't bad at all to slice in S3D. Only took about 30 seconds. I can't see any glitches in the preview, but I don't want to try to print this thing with (or without) supports generated. So I guess the only way is some custom gcode.

Or it could be sliced into wedges, which when laid flat on the bed would each be printable without support, but I think the seams would not look so good with the lithophane effect.

[Tim]

Well, the cylinder that I printed crashed S3D about 3/4 of the way through (and yes, I ought to have known better and put the thing on the SD card), but I just printed the top quarter separately and glued the two pieces together, and it's not half bad. So probably the world map globe could be done in wedges and not look too bad. I wouldn't try that with a photograph, though.

With the cylinder, I read it into S3D once and it made the entire middle half of the cylinder completely solid. I read it in again later with exactly the same parameters, and it had no errors at all. There are some very screwy things about S3D. I have not yet read the globe in without an error, even though it is perfectly manifold. Glad you got it to work on the first go! Could be a problem restricted to the 64-bit LInux binary for S3D, though. But I've seen the behavior mentioned before.

By the way, bear in mind that binary STL format is only marginally less stupid than ASCII format: Per facet, there are still three words for the normal vector that could be computed from the vertices, and then there are 2 completely useless bytes added on for good measure (although there are variations of the STL format that uses those bytes for a material description). And all shared edges are written twice, and all shared vertexes are repeated as many times as there are facets containing them. But, yeah, the ASCII is between three and four times the size of the binary format. I need to remember to use the "-b" switch.

[Toby]

Yes, there are some screwy things with the S3D slicer. But it does get better each release. My guess is what's going on is that it's using random numbers here and there and so each time you slice it really is different though the inputs are the same. Then after that even a small rounding error could lead to a big mistake in the interpretation of what is and what isn't part of the model. Just guessing though.

For some reason I've had a string of good luck and I can't remember the last time I got a bad slice from it. I'm on a 64 bit PC. One would assume the slicing part of the code isn't dependent on operating system, but who knows.

I've been using .obj files for the models I create in software. It's still ascii but at least the floating point vertices are written only once and thereafter referenced by index. I can see how .stl made sense for stereolithography in the beginning, but for general purpose modeling or FDM printing it's pretty lame.

I was thinking the world map could be cut into wedges along the latitude lines and then printed. Just fortunate for this particular model to have that option. What is the best kind of printing material to get the lithophane effect? All I have right now is colored PLA and ABS.

[Tim]

The flat lithophane and the cylinder were both done in purple PLA, which is what I had in the printer, and I was too lazy to swap it out for something else. Right now I'm about to repeat the process with white PLA (from MakerGear). Although, since the purpose of the lithophane is to shine light through, if you plan to put it in a window or in front of an incandescent bulb, PLA is going to have a high risk of warping under the heat. If you have it in a shadowbox with LEDs behind it, like the one Jim posted a picture of, then PLA is good. I'm planning to do the same thing with a 5" x 7" shadowbox I got from Michael's Arts & Crafts, with the same LEDs that Jim recommended, so the PLA should suffice.

[jsc]

Light, non-transparent plastic works the best.

Tim, I think you're seeing the same sort of bug that fills holes with a single layer sometimes that I mentioned in my S3D writeup. Try adjusting your first layer height by a percent or two to see if it helps clear it up, or adjust your layer height by a tiny amount. I think it's some floating point related issue.

[Tim]

Thanks, Jin, I'll give that a try (so that's where I remembered the hole-filling behavior from!). Still, a fix would be nicer than trying random adjustments until it works. Particularly when the size and complexity of these spheres, and the tendency of S3D not to release memory that it has allocated for toolpaths, means that I have to shut down S3D between attempts, or else it will fill up my memory and start page swapping.