I printed the forearm as two pieces for top and bottom (4 pieces total) and glued together as per instructions. Since I print with ABS plastic , I typically use the acetone glue method, however for the top and bottom of the forearm the mating surfaces don’t have uniform contact so the joint was weak. So after tacking with acetone glue I injected gap filling super glue very generously and then let is sit a couple of hours. Now it is very strong.
One issue I came across during final assembly was breakage right in the middle of lower piece. Which I though was disastrous, but turned out OK because it forced me to add long 0.8mm thick strips of ABS (acetone glued). You can see the strips on the image above ( I wish I would have printed them out of black for artistic touch!). This arm assembly is now very strong and I don’t worry about breakage as much any more

as per above I posted above this is 2 pieces and needed to be glued together. Since I use ABS plastic for my prints. Splitting is a real problem for tall thin items which only get worse for really all items. Lower shrinkage plastic – like PLA may work better for a combined part.
I consider this version a prototype and I have decided to start work on a design of a new arm that eliminates the need for gluing (except the strengthening strips). This will work better for the 13-14 yr old kids I work with at the middle school as they have only limited time during school and may build, take apart and rebuild the arm multiple times .