3D Printing and molding the brace:
This next step is when you will need to print out the design using a 3D printer and then mold it to fit the arm. I'll share with you how we did it, including how we created a cast of my daughter's arm to use when molding. Creating a cast turned out to be something that may not be needed, so I'll leave that as optional.

 3D Printing:

   
If you are 3D printing using a service like Shapeways, then most of the settings and fixes will be done for you. Here are the points to make sure of:
  • Print using PLA plastic! PLA can be molded when heated. Other plastics cannot be molded when heated!
  • Make sure you check the mesh integrity (Shapeways did this for me)
  • Wall thickness should not be too thick (Shapeways checked this for me)
  • The INFILL setting of about 50% (Shapeways did this for me)
 
 
Molding the braces:

   
PLA plastic can easily be molded when it is heated. We created a cast of lorelei's forearm and upper arm and I'll describe that process below, but creating a cast may not be necessary if you have something that has a roughly similar shape and circumference of the arm, like a bottle or pipe.  
  1. Lay out the flat 3d printed arm braces and link them up so that the joints of each brace clip together. There may be rough edges on the joints and now is a good time to file them off with sandpaper or a nail file. Make sure you understand which way the brace will need to be molded so that in the next step you are ready to quickly do so.

  2. Get a large baking dish, some boiling water and the object you will use to mold the brace around ready. Place the 3D printed arm brace in the baking dish and pour the boiling water on it, in a few seconds it will be flexiable. 

  3. Quickly take out the braces —makeing sure not to burn your hands— and mold it around the cast or some other shape that closely resembles the shape and circumference of the arm. Note that at this stage it will not be in the perfect shape and fit, that comes a little later. 

  4. Once you have the two braces in roughly the shape you want them in, clip them together by the joint and find a long nail, crochet needle or something else to stick through the joint holes. At this point you may need to heat up the braces again around the joint area, this is where you need to use a hair dryer. mold the braces so that they are perfectly aligned with the rotation axis. Note: that in the next version of the brace we may design a better joint with less friction, but for now this approach works just fine and makes the design really easy to experiment with.

  5. Now try fit the braces around the arm. I usually unclip them to fit them then clip them together when they are on the arm. Remember to clip them over the clothing as it may pinch the skin if it is worn directly on the arm. Make sure it fits well and that when it rotates it does not pinch the skin. You can tweak the fit with a hair dryer after you have again removed the braces from the arm.  
 





 
Optional: 

   
We made a mold of Lorelei's forearm and upper arm for this project. This allows us to mold the arm braces around the casts while they are hot from the boiling water.

To create the mold we used Alginate and followed this video: https://www.youtube.com/watch?v=145TDzTXluU but instead of using rubber to create the final cast we used plaster.  Make a small mold of a hand first just to test out the process and get a feel for the mixing ratio. We used a more fluid mixture and colder water so that we had longer to get the arm into position. 

We ended up creating two separate casts, one for the upper arm + joint, another for the forearm. This allowed us to easily mold the two braces.
 




 
Step 1 - Understanding the problem
 
  Step 3 - Measurements & 3D designing