This converts a child's toy crossbow into a soft tipped dart launcher. I wanted to make a fun dart launcher as a gag gift for my brother-in-laws dart club. I took a kids plastic crossbow and replaced a few parts and now I have a proper dart gun that can shoot a regulation plastic tipped dart 8 feet or so.
I based this around a kids gun so it would not become a weapon, I did not want anyone to get hurt when playing with it. This lobs the dart about as hard as you would throw them by hand.
The crossbow I based this off of can be found here on amazon: http://amzn.com/B07DMQGZB7
And the darts pictured can be found here: http://amzn.com/B003K0LWR2
I printed this on a stock Creality Ender 3 using the default 2 mm draft profile in Cura with Amazon brand green PLA. The top plate is quite long at 285 mm and just fit on my ender3 when I rotated it 45 degrees on the bed and turned off the skirt. You can remove the last 35 mm or so from the piece if you can't get it to fit on your printer, the back end is just there to fill in a hole in the base of the handle.
To make this shoot farther make sure there is no binding of the parts and smooth down any rough edges. You can also remove one of the blue and yellow end caps on the crossbow and tighten up the elastic cord. I shortened my cord by about 30 mm although I don't know that it was needed. Finally the front originally had a green piece with a cross hair on it. This piece is needed to hold the bow of the crossbow in place, but it interferes with the dart and so I cut it off flush with the top plate so the dart could pass smoothly out. This is fairly weak plastic and can be cut with wire cutters, however I used a hacksaw and filed it smooth to make for a cleaner result.
The whole thing can be assembled using the parts that came with the gun. There is a single screw at the front of the top plate and two at the back on the sides that hold it together. In addition there is a metal pin that holds the trigger on to the top plate, the pin goes on the back set of hols on the top plate. The holes are slightly over sized, so I put a piece of tape over them to keep the pin from falling out when assembling this, it saves some frustration. The trigger is installed with the round spring facing the back, and the bottom part of the glide has a notch in it that the front of the trigger clips onto.
This was designed with a education licence version of fusion 360, and more time than I originally intended to invest! It was a fun project and I learned a lot so it was time well spent in the end.
Edit: added a shortened version of the top plate so you can print this on a smaller printer.
Edit: now with a Laser! I made a laser pointer holder that clips onto the dart holder. It can be adjusted in elevation, but not side to side. The accuracy is not bad, if you take into account the lack of adjustment side to side. I used this laser pointer from amazon: http://amzn.com/B07BPT1NMT