The original was in no condition to be repaired. After years of exposure to the elements, it had cracked in half. Gluing it back together wouldn't fix the other problem, which was that one screw could not be used to secure the handle- due to a large hole along the crack line.
The original, however, was in perfect condition.
So I began on the 3D model. At this point, I was most comfortable with FreeCAD as a 3D modeling program.
The fact that the original handle had cracked in half was a boon to the 3D modeling process. It made finding the thickness of the bottom and other parts of the handle much easier, because I could measure them with calipers. I couldn't do this on the other screen door handle, because it was in one piece.
Here's a picture of the underside of the original. I made a couple design decisions when creating my replacement handle, and among them was the decision to omit any of the original's plastic injection molding marks.
The 3D-printed replacement also had to accept three screws; two were used to attach the part to the door, and one was used to attach the handle to the mating handle on the other side.
The screws were rather ordinary. However, one of them was missing from the handle that I had to replace. (This screw was the one that mated the handles together. Due to a large hole in the original plastic handle, it fell out and disappeared.)
This print was done in grey PLA, on blue painter's tape. I started out in 3D printing with blue painter's tape as my printing surface, mainly because it needs no heat from the heated bed and because it works very well for PLA adhesion.
This print needed supports under one half. You can see the supports being printed on the upper and right sides of the print (they are the squiggly lines).
Here you can see the supports finally being filled over with actual plastic. The messy covering on the left area of the part is the beginning of quick bridging to create the supported surface.
The screen door handle, after printing.
As expected, I had to clean off the supports. I put them on the bottom, so nobody can see them.
Amazingly, the handle fit properly on the very first try.
The screws even fit correctly in the holes of the handle. I was gambling that I would have to reprint something, but I was happily wrong!
It's this sort of project that makes me feel like 3D printing is useful for something with a purpose.
Interested in printing your own screen door handle? You can grab the files from Github here.