Wednesday, September 28, 2011

Triangular Dovetail Joint

Woodworkers have made trick dovetails for years, probably centuries.  I designed this trick joint because I hadn't seen any triangular dovetail joints.  Not surprisingly, it has been done before.

All three exterior sides show identical dovetail-like joints, which makes it look impossible to open.

But the pieces don't slide like a conventional dovetail.

The two pieces rotate until they gently let go of each other.

There's a hollow cavity inside, so it can be used as a puzzle box.  Not that anyone would be terribly puzzled--it looks odd, but it's easy for anyone to open once they pick it up.

This is a simple, traditional puzzle box so I've posted the STL files at Thingiverse for anyone who wants to play with it.

Tuesday, September 20, 2011


Schorhr's Spring-o-sphere model on Thingiverse looked like a perfect example of a model that's unsuitable for building on the SD300: very thin walls surrounding a large trapped volume.  But that made me curious, so I included the Spring-o-sphere in a batch of models back in June.

I anticipated there might be trouble peeling the support material away, so I put a box of peeling cuts around the Spring-o-sphere so it would be isolated in its own little 'brick.'

As expected, it was tedious peeling away all the enclosed material a tiny bit at a time.  Right at the start the little hook broke off the top, so I expected more breakage.

But the rest of the material peeled away without any further breakage.

The body of the spring proved to be surprisingly resilient.  On close examination I could see lots of little loose ends.  These are unsightly but they don't seem to weaken the spring.

Evidently this unexpected resiliency was imparted by the long overlap between layers.  There's exactly 1 layer of red material in the model, but red band shows how that layer extends a long distance around the spring, thereby giving it ample distance to be bonded with the layers above and below.

It's a nice container for holding shiny objects.

Despite my relative success building this Spring-o-sphere, I still regard it as a model that's basically unsuited to the SD300 build process.  But the experiment suggests I could choose to build such a model in a pinch, provided I'm willing to sacrifice the model's visual appearance (eg: broken hook, loose ends) and invest extra effort (eg: repair hook, tedious peeling).  I certainly wouldn't recommend doing this sort of model routinely, but it's nice to know I could.

Sunday, September 4, 2011

More Assorted Stuff

I like puzzles, so I built this Mysterious Wood Joint in transparent material. According to its creator, the joint was adapted from a wood joint used in Osaka Castle. At first glance it looks impossible, but the pieces go together easily when oriented correctly. I wonder if the design could be further modified to make it more like a puzzle.

An SD300 user sent me a picture of a chain they'd had trouble building, which inspired me to attempt one for myself. Problems had occurred when the chain was positioned with alternate links vertical & horizontal like the yellow chain at left. When I built the chain, I positioned it so all the links were positioned at 45° angles relative to the build platform.

I built the model with a single peeling cut running down the center of the chain, which allowed the first half of the support material to peel away easily. But I had to fish out scraps of leftover material behind the links.

After peeling away the other half of the support material I had to fish out the last scraps with tweezers again. But that's okay because it took only a few seconds for each link.

The finished chain had a uniform texture.

I built a 50% scale version of Free Falling Maple Seed becauseI needed an arbitrary model at least 2 mm high to get some layer-thickness measurements from the SD300. The layer lines form attractive, delicate patterns.

These 45-RPM record adapters required minimal material because they're only 2 mm thick.

To add color to the adapters, I stopped the SD300 halfway through the construction of the model and scribbled between layers with permanent markers. This is the middle layer in the model; the color showed through after the rest of thelayers were bonded above this.