My friend got a kids ride-on dirt bike and it had a few problems.  The spacers that go on the axle between the rim and forks were not in the package, the headlight's did not turn on and one of the hand guards was cracked.  I started with the missing spacers.  I assembled the rim, axle and forks to get a measurement for the spacers.  I measured the open space with my calipers and it was 39 mm.  The axle had a 10 mm diameter.  This was a easy part to make.  I need to parts that were about 19 mm tall.  I printed them at 16 mm tall to allow for some extra room.  I used Sketchup to make the spacer and saved it as a .stl file.  I converted the fle to a .gcode using Sli3er.  I printed the part with 20% infill and with .2 mm layers.  It took about 40 minutes to print both the parts at once.  I decided to tackle the other problems during the print time.  I put a piece of filament in my Dremel and friction welded the broken hand guard.  I got my meter out and test the voltage at the connector for the headlights and there wasn't any.  I had to remove the boxed that housed switch, buttons speaker and batteries  to be able to open it up.  The problem was easy to find.  One of the wires was unsoldered.  I looked around and found the spot where it was soldered to.  I doubled check the spot with my meter and it was 3 volts.  I soldered the wire on and hooked up the connector, flipped the switch to check if it was working right before reassembling everything.  I got everything back together just in time for the 3d printer to cool down.  The hole diameter was a little bit to small, so I used a drill it out with a 10 mm drill bit.  None of these repair's were necessary because I'm sure the company would have sent a replacement, but it probably would have took a month to do.  I was able to get everything fixed in about an hour and the child can ride the bike today.  I used a Da Vinci 1.0 to print the parts on.