Wednesday, January 6, 2016

3D Printed Mineral Display Bases

When you see fine mineral specimens on display they're typically sitting on a clear acrylic block into which someone has routed out a cavity for the specimen to set into.  These can make a $100 specimen look like $1000, and they add a lot of value to the item.  Last year I started thinking about using a 3D Printer to create custom bases for our specimens, so I did a lot of research on the topic, and concluded that the reason that nobody had done it yet was that 3D printers were still a long way from prime-time.  The speed, quality, and reliability of the 3D printers out there is quite sub-par, and is really only useful for people tinkering around.  That being said, there is a new generation of 3D printers on the horizon which look like they will finally make this a possibility, and we're hoping some of them hit the market later in 2016.

After much brainstorming I've figured out all of the steps necessary to make this all work:

STEP 1:  Create a 3D Mesh of the Specimen's Bottom

There are new technologies out there which can allow you to create a 3D model of an object without the use of expensive laser scanners.  One such technology only requires a handful of photographs of the object from any digital camera.  Using Memento from Autodesk, you can photograph your specimen, drop the photos into the Memento application, and then wait for the Autodesk servers to work their magic on them.  A short time later a very high-resolution, and highly accurate 3D mesh will be sent back to you.  From here you can export it as a data file such as .obj or .stl, and this file can then be imported into any 3D modeling application.  As of this writing, Memento is 100% free!  You can create all the 3D meshes you want for $0.00, so forget about having to buy a $20,000 laser scanner.

One problem that this technology shares with traditional scanning methods, however, is that it tends to have problems with objects that are shiny or transparent, and mineral specimens have a nasty habit of being both.  So, a common solution is to make an impression of the specimen in some sort of molding compound.  If you've ever been to a podiatrist then you're probably familiar with the compression foam that they use to make an impression of your feet.  This stuff works great with minerals too!  You simply push the specimen into the foam to make a negative impression of it.  Then you can photograph this impression and have Memento generate a 3D mesh from that.  This is the same basic method that orthotics companies use when your podiatrist sends them that foam impression of your foot:  they scan it into a computer, and then that scan is used to construct a custom orthotic that fits your foot perfectly.  We're essentially doing the same thing here.

One important thing to keep in mind, however, is that Memento has no idea what the size of the specimen in the photos is anymore than it knows the size of a person in a photograph.  It needs a frame of reference.  So, a simple solution is to buy a 1cm scale cubes and include it in the photos.  When you get the mesh from Memento there is an option to set the scale.  You select two points on the mesh and tell it what the distance is, so you'd simply select a corner of the cube and then another corner and tell it that the distance is 1cm.  Memento will then scale the entire mesh to fit that size, and it should be extremely accurate.

Since there may be a little fluctuation in the scaling and printing of the object wiggle the specimen around in the compression foam (if you're using that method) to give it some margin.  You don't want a glove-tight fit, but rather just a fraction of a millimeter of breathing room.
Add your photos to Memento.  The more the better!
Then wait a while for Memento to work its magic

When complete, you should see a 3D model which you can now export

STEP 2:  Construct the Base in 3D Modeling Software

I'll be honest, this step is not for the faint at heart.  Using 3D modeling software is something that takes a long time to learn.  I've been at it for almost 30 years, and I'm still learning new techniques.

The 3D modeler I recommend is Blender.  It's free, well supported, and does everything you'd ever need to create unique display base designs.  Blender can import the mesh that Memento generated in Step 1.  From there you simply construct your base around it.  I won't go into the details since it's a complex process, but the short version is that you build the base geometry, and then use boolean operations to carve the specimen's description/locality text into it.  The same boolean operations are then used to apply the imported mesh into the base model.

There are some caveats that you need to keep in mind when modeling for a 3D print, mainly that your final model needs to be air-tight.  No holes or overlapping parts.  There is a lot of information on the internet about how to build a proper model for 3D printing.

Import the model into Blender
Build the 3D printable model of the base in Blender.

STEP 3:  Print It!

Once you have the model all you have to do is save the file and send it to the 3D printer.  There might be some final touchup, but that's really all there is too it.  If you did everything right earlier (got the scale of the mesh correct) then the printed 3D model should be a perfect fit for your specimen.

However, this is where things get more theoretical than practical.  As I mentioned in the intro, current 3D printer technology basically sucks.  There are two basic types of 3D printers:  ones that ooze out extruded molten plastic to slowly build a 3D object layer by layer, and ones that use a projection system and UV light to instantly harden a liquid polymer layer by layer.  The extruded plastic printers are notoriously slow, unreliable, and the final prints are not particularly accurate and have rough edges.  They're terrible at doing sharp angles.  The polymer printers (also known as stereo lithography - STL printers), tend to be faster, more reliable, and have much better detail and accuracy, so this is the type of 3D printer you'd want to use.  The main issue is that STL printers are very expensive, the photopolymers are expensive, and certain parts need regular replacing.  They're a little faster than extruded plastic printers, but they can still take hours to print simple, small objects.

What's on the horizon will likely make things a whole lot better.  There are new STL printer technologies that have been demonstrated which will reduce printing times from hours to minutes.  Carbon3D recently got $100 million in funding from Google, and their printer could show great promise.


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  6. Late to the party, but what about starting with a block of acrylic, then cutting the impression into it, with an engraving machine or CNC machine? I think that's how most custom bases are made now. I know CNC's are not for the casual home user, but I wonder if there are machines out there that can accomplish something similar without the expensive cost...?

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