Wednesday, May 29, 2013

Not-so-wonderful Waterful

Inspired by a wasp trap, a friend suggested a water-filled dexterity puzzle that challenges the user to guide a floating ball into an inverted funnel.  It's a cool idea, but why not use two balls: one that floats and another that sinks.  I designed a two-piece box that had transparent windows and two funnel-shaped goals.

I put two little balls inside and sealed it full of water.  One ball is polypropylene, which floats, while the other is made of PTFE, which sinks.  The challenge is to get the floating ball into the funnel at the top and the sinking ball into the funnel at the bottom--at the same time!  My first test model seemed to work perfectly.

Problem!  The PVC windows gradually fogged up as the PVC absorbed moisure.  After a couple of days it turned completely opaque.  This effect is reversible: it turns transparent again if it dries out, but the puzzle needs to be filled with water so this design just wasn't practical.

So I tried a different approach: I incorporated the funnels into two caps that could be bonded to a piece of acrylic tubing.  Acrylic doesn't absorb moisture so it would stay crystal clear, right?  I assembled a test model and filled it through a fine needle and sealed it up.

This worked much better: the side walls were perfectly clear and the cylindrical shape worked like a lens.  Here's how it looks when solved, with the floating ball in the funnel at top (barely visible) and the sinking ball in the bottom funnel.  At first it seemed perfect: no fogging, no bubbles!

But a small bubble appeared a few days later, and gradually grew.  After two months it had grown so large that it interfered with the balls, and it's obviously going to keep growing.  So this won't work, either.

Although the containers seem to be watertight--no leaks--I'm guessing the PVC isn't vaportight.  So the water vapor could be escaping by diffusion through the PVC end caps.  But my coworkers liked this puzzle while it worked, so it's worth another try.  Back to the drawing board!

Tuesday, May 28, 2013

SD300 Issues from emails

Through email I've learned a lot of tricks and solutions to SD300 issues.  Occasionally I've relayed a solution from one user to another, who then devises an improvement of his own.

A user in Romania found his Anti-Glue cartridge had dried out while the machine wasn't being used, so here's a trick I learned from a British user: add water to the cartridge by injecting it into the breather hole with a syringe or needle-tipped squeeze bottle.  (49 gauge fits)  One user drilled a larger hole and refilled it through a funnel.

This technique could also be used to extend the life of an Anti-Glue cartridge in case you've spoiled one.

Occasionally users have reported an odd phenomenon where unused support material doesn't tear away cleanly because the layers are stuck together and the unused plastic has a gooey, melted texture.  I'm not sure it's the same, but I recently experienced something like it while cleaning the model in the picture.  Most of this material is unused support material.  It should all be shiny like the area at lower left.  The problem area is at top-right, which didn't peel away cleanly.  Each layer of unused material was littered with tiny spots that were tightly bonded to the layers underneath--and it appears that the shiny Anti-Glue film was interrupted by little spots where the layers were unintentionally glued together.

My first theory was glue might have dripped after ironing a new layer to the top of the model block, as pictured in this previous post.  So I watched the machine carefully during the next build.  No droplets.  But when the machine applied Anti-Glue there were spots in the film--holes through which glue might unintentionally bond the base layer to the model and support material.

I watched more carefully as the machine ironed the next layer of material, and noticed it already had smears of glue across the top surface--right out of the feeder!  How was that even possible?

Aha!  There were scraps of plastic clinging to the underside of the iron bridge, which contains the jets that spread glue on the top of the model.  My current theory is that those scraps hung down enough to touch the PVC as it was being rewound into the feeder, drawing glue into the feeder by simple capillary action.  Right or wrong, the issue hasn't occurred since I cleaned around the glue jets underneath the iron bridge.

It's not obvious how to get access to inspect and clean the underside of the iron bridge so I made a video.