Monday, January 14, 2013

Evaluating Protomold and Moiré Maze

A friend from IPP suggested I investigate a company called Protomold for their expertise in rapid injection molding and wide selection of materials.  Although he was not a puzzle builder himself, he had apparently sponsored production of another designer's puzzle via Protomold and was pleased with their work.

As an exercise I chose to adapt Moiré Maze, a design I briefly tested in 2009.  The original test model contained 5 layers of transparent laser-cut acrylic containing ring-shaped channels.  The goal is use a magnetic wand to guide a small magnet through the channels from start to finish.  The lowest layer is a mirror, which I hoped would create an illusion that would disguise one secret feature so its solution could literally hide in plain sight.

I gave the prototype (pictured above) to several testers, and their toils demonstrated the secret feature was a success.  But the maze as a whole was much too elaborate, the nine pairs of overlapping rings merged into a dizzying kaleidoscope of curves.  The key feature worked, but testers agreed the overall maze was just too complicated.

So I consolidated the inner layers of Moiré Maze into a single 3D model, simplified the maze to just six rings, and added details for a built-in stand that could be injection-molded in a standard 2-part mold.  I requested a quote from Protomold, and in the meantime I built a test prototype on the SD300.

As it turns out, the SD300 is great at building a model that's designed for injection molding because there aren't any overhangs to get in the way while cleaning unused material off the model.  I did need to use a fine probe to clear the smaller channels, but it was easy because I had unobstructed access from both sides.

Both sides of the model needed some sort of lip to hold the cover pieces, so I designed these little tabs.  This tab is an example of a sliding shutoff.  It looks like an overhang but it really isn't--the other half of the mold would project through the hole in order to form the underside of the tab.

It's always good to build a prototype: during inspection I discovered an error in my maze.

Upon correcting the error I built another test model, this time using the SD300's transparent material because the user is supposed to see through the mazes.  My PVC material isn't nearly as transparent as acrylic, and there are blemishes from the SD300's construction process.  But it's an excellent test model!

Also using the SD300, I built a pair of transparent covers.  Above, I installed the back panel into the test model.  The back panel ought to be cut from acrylic mirror material, but a simple transparent panel would suffice for testing.

I dropped a small magnet inside and then installed the top cover.

The challenge is to navigate the maze from start to finish by using a magnetic wand to guide the little magnet through the channels between the two covers.

Protomold replied within 1 business day, giving me an interactive quote that enabled me to gauge the cost of various options.  These folks obviously know their business!  Their versatile quoting system permits the customer to view and evaluate their quote in four distinct ways, at the user's discretion:
  • As a straightforward web page (pictured above) with tabs and interactive elements.
  • As an enhanced web page with a powerful 3D plug-in.
  • As a printable PDF document with all the information comprehensively laid out.
  • As an enhanced PDF document that exploits Adobe Reader's ability to view 3D models.
The report called attention to six "required changes" that would need to be addressed for the model to be injection molded.  Five of these were the result of a single error in my model, which caused an undesirable indentation in the walls.  Pictured above, Protoquote's interactive plug-in highlighted the error and explained exactly what action was required and why.

Additionally, the report explained the ramifications of certain attributes that might have cosmetic or functional ramifications on the finished part even though they wouldn't prevent the model from being built as-is.  For instance, the blue marking show where "sink marks" could appear in the finished model because injection molded plastic shrinks as it cools.

After I resolved the "required changes" Protomold supplied an updated report.  Now that the model was completely build-able the report added an informational section calling out foreseeable (but harmless) side effects of the tool-making process.  Pictured above is a sample of the "Printable PDF" version of the report, denoting where sharp corners would come out very slightly rounded as a machining artifact.

It was a valuable experience, and this particular model was probably an ideal choice for learning how to make an injection-molded design.  But, in my final analysis I concluded injection-molding isn't suitable for this particular project in the quantities I needed because:
  • This particular design still required laser-cut parts for the mirror and top cover.  Injection molding merely reduced the volume of laser-cut parts per model (from 5 down to 2), it didn't eliminate laser cutting entirely.
  • To attain the required transparency the molds would require laborious polishing to a mirror finish.  That polishing would cost more than all other expenses combined, which rendered the project hopelessly uneconomical for a small production run.
  • Critical geometry includes a knife-edge "gore" where two arcs converge toward an intersection, a feature not suited for injection molding.  Hence injection molding would diminish the quality of that particular detail.
  • The previous test model had already demonstrated the design was suitable for being laser cut.
Still, it would be nice to devise a design that would be optimal (and economical) for injection molding--preferably something I couldn't otherwise fabricate.  Protomold offers a wide selection of engineering materials, including elastomers.  Hmm.  I have an idea that could use Santoprene...

1 comment:

  1. A very interesting post Scott. I have also been looking at Protomold's service as I have a project that most probably is suitable to be injection molded. Protomold offer a great selection of help files, technical documents and samples to interested persons who register with them. With regard to your project I see a link to a puzzle called Boston Subway which although very different to your design (by the look) also is a maze with a magnetic wand. Boston Subway was made by George Miller and I believe it was laser cut as your puzzle will be (by the sound of it).