Tuesday, June 28, 2011

Assorted "stuff"

I'm continually building models and often forget to share them, so here are pictures of some recent projects.

I built a three-piece puzzle in transparent plastic. While it was building I used a permanent marker to add three splashes of color between layers, using the technique from an earlier post.

Once assembled the transparent material catches the light and the colors seem luminous!

I built this simple-but-elegant Mini Stand for iPhone & iPod Touch. While it was building I switched between black and white material to incorporate a subtle, decorative stripe. It's a small model so I built 3 of them side-by-side using no more material than just building 1.

A Thingiverse user created a script for Duplicating House Keys using the free OpenSCAD tool to create the model data. But it only makes keys for old Kwikset KW1 lock cylinders, so I think it'd be interesting to update the script for the newer KW10 models.

This Recursive Reuleaux Triangle is the first model I built that was pre-assembled. The parts were built already-interlocked in grooves so the triangles can slide around freely but they can't come apart.

Pixobox Studio provided the data for this detailed figure of a Human Head. I had reduced its size to 28% to fit it within volume left over for another model I was building. The Z-axis layering is plainly visible at this low resolution, but it has excellent XY surface detail. There's some tiny text on the sidewall, just below the chin.

Here's a view of the back of the statue, showing the surface details in the hair and more tiny text carved into the back wall of the figure.

Last month I ran into a challenge trying to disassemble part of my car. This spring needed to be tightly compressed to open another access panel, but it's offset from the opening where it's awkward to reach with ordinary tools. So I simply built my own tool with the SD300.

So I 3D printed this simple plastic tool, which has two built-in elbows that reach around and compress the spring. The tool has 1cm thick walls, so it was extremely strong...which was lucky because I had to be surprisingly forceful to release the spring completely!

Tuesday, June 14, 2011

Building hollow parts "as solid"

Unlike most other 3D printers, the SD300 builds solid parts faster than hollow ones of the same size. Hollow parts require just as much material as solid ones, so I generally make my designs as thick and solid as I like.

But I know many designers who optimize their designs for Shapeways White Strong & Flexible material, so they typically design hollow parts with very thin walls to minimize costs. The SD300 isn't very suitable for very thin freestanding walls, but could I build such models if I just left the support material embedded inside? Would it sacrifice functionality or strength?

A colleague graciously lent me a set of STLs that had been optimized for the EOS with exterior walls only 0.8mm thick and I set out to build them with peeling cuts arranged to leave the support material trapped inside.

I built a small batch of test parts without any trouble. Because the support material is trapped inside they feel like ordinary solid parts, but they aren't quite as transparent as solid parts usually are. The interiors are somewhat cloudy, undoubtedly because the SD300 cut and masked the material inside to facilitate removal. They looked perfectly acceptable, although I have my doubts about their durability.

It went well enough that I tried another batch, then another. A big piece broke off while I was peeling the last batch of parts. The chip (at top right) is still attached to the support material, and the pin is pointing to the surface where the chip broke off. If you look carefully you can see the thin, triangular border which was the only region that had held it together. Not surprising, really.

I repaired the break by putting the piece back and running welding solvent (Weld-On 2007) over the model. The solvent helped glue together the surface of the model, but the support material remained safely un-bonded so it could still be peeled away. Apparently the SD300's Anti-Glue coating works against Weld-On.

I test-assembled some of the parts; they didn't fit together as accurately as parts built from solid STL data. That makes sense in hindsight. Using "hollow" STL data meant the interior material wasn't continuous because the SD300 had made cuts for the interior walls and had masked the interior layers with Anti-Glue.

So the experiment answered my basic question, could I build STLs that had been optimized for EOS or other thin-wall technologies? Yes, I could build test models with restrictions on their usefulness:
  • The support material would have to be left inside, so hollow STLs built as-solid would be much heavier than a hollow model built on an EOS.
  • Such models would not be as strong as solid models, despite their solid appearance, because the interior isn't bonded together like solid models.
  • Such models aren't as dimensionally accurate as models build from solid STL data.
  • Such models aren't as transparent, even when built with transparent material.
If I intend to build parts on the SD300 I would not design them with thin walls like these, but the technique is potentially useful for verifying the basic size, shape, and dimensions of STL data that's optimized for another build process.

Wednesday, June 8, 2011

Efficient peeling cuts revisited

Here's another example of how to arrange peeling cuts for efficient cleaning of an SD300 model. The user adds peeling cuts (the purple walls) while preparing to build models in the SDView software. Peeling cuts don't affect the model, but they instruct the SD300 to cut the support material that surrounds the model so it can be torn away conveniently.

When I had just learned to use the SD300 I tended to put peeling cuts between each individual model to isolate them, resulting in lots of small areas that had to be cleaned one-by-one. But I eventually learned to arrange models so the peeling cuts could be joined and streamlined, peeling several models at once.

These nine models have two continuous peeling cuts that follow the geometry, so the two exterior regions can be peeled away in an easy continuous motion.

After the two outer strips have been removed the models are still connected by leftover support material between them. Much of this can be peeled away in the same manner, as the top and bottom areas are continuous just like the other strips were.

There's still some support material embedded in the middle layers between models, but it doesn't have to be removed layer-by-layer like the other strips. Instead I just loosened up the support material by squeezing a probe between layers in several places...

...then I gripped two adjacent models and gently twisted them to-and-fro, which gradually loosened the support material between the two adjacent pieces. In about 10 to 15 seconds the leftover material was loose enough to free the two adjacent pieces, and I moved on to the next pair of embedded models.

All told, it took less than ten minutes to completely clean these models. The same batch of models probably would've taken a half hour or more if I had isolated them with individual peeling cuts. Back when I was just learning to peel and clean models it probably would've taken over an hour, so experience helps too!