For me, the first step in building anything is always to test it out. Especially when the finished product is something with moving parts, it's very important to have a physical object in my hands. No matter how many times I spin it around in 3D in the computer, there are always surprises when you're dealing with physical objects.
Step 1: Simplify the 3D Model
Although the Objet 3D printer can print at incredibly high resolution, you have to tweak things a bit to be able to make a moving physical object at a small scale.
I replaced the models for bearing & shaft assemblies with simple holes and pegs- this allows for the movement I want to test without trying to rely on the parts I downloaded from McMaster Carr.
Since I did the first draft of the model in a nurbs modelling program, I had to create meshes from my nurbs in order to get the STEP file that the printer can read. I took this process as an opportunity to combine parts of the model that would make for a simpler super-glue assembly once it's printed.
I also took this opportunity to split the parts of the model that had more "volume", i.e. the roof enclosure and the doorway enclosure, and laying them on their longest sides. I had to super-glue these together later, but it significantly cut my print time and support material usage.
Step 2: Preparing Files for the Objet
For this machine to print, the meshes must be clean and have no openings. In the Objet software, you can verify the geometry before printing- it then shows you which parts aren't going to work.
Netfabb is a super easy (and free!) way to repair your meshes with the touch of a button. Once the meshes are repaired, all you have to do is assign material and you're ready to go.
Here's a useful tip one of the other AIRs pointed out: the Objet printers have 2 printing material cartridges. If you're only doing one material, put two cartridges of the same material in the printer. Your printer essentially goes twice as fast as if you were only using one cartridge!
Step 3: PRINT
Sending the files to the printer is super easy! It's really not much different from an inkjet printer when it comes down to the interface. This print took about 7 hours to complete.
The printer uses UV light to cure the layers of the model as the head passes back and forth. The print material is encased and underpinned by "support material", which basically means your part is encased in this hard jell-o when you're done. It comes off using a pressure washer spray booth, it comes off really easily if you soak it in water overnight.
Step 4: Assemble the Parts
Assembling the parts using superglue was pretty painless. I used the Vero Clear material and some generic liquid super glue. The walls of my model were about 1/16" thick, and gluing them edge-to-edge this way was no problem.
Step 5: Attach the Moving Parts
I made little posts and holes in 3D file before printing, then quickly realized they were way too small when printed to support the movement in this material. A quick solution for this was to use some small 4-40 machine screws I had lying around and do a little tapping- basically just slowly screwing the screws in and out of a drilled hole in the 3D model. This did the trick, allowing me to test the movement of the parts with no trouble.
Step 6: Lessons Learned
1. The window on the door is way too wide. It only leave about 3 inches of material altogether to support the whole bottom half of the door. This is the kind of thing I would expect to have worked out the computer long before fabrication; just goes to show you how useful a scale model can be!
2. Surprisingly, the roof element is a lot more sturdy than I expected, and the door element is a lot less so. I've decided to integrate the floor element into the swinging doorway to make it more rigid.
3. The floor is also very sturdy, I won't need to be doing a lot of blocking to make it sturdy.
4. It looks cool on my desk, and everyone wants to touch it.