My son wanted a crane for his wooden train. I created this with various things I had on hand. It's not particularly attractive, but he does not seem to mind.
I am very happy with how well the printed parts work with the dowel rods in this project. I certainly will try and incoporate cheap building materials like dowels or PVC in future projects.

Required parts that are not printed:
String
1/4in OD water tubing (6.35mm)
Small wood screws (#4x3/4) + plus some larger screws for anchoring the base.
5/8in dowel rods (15.875mm, mine vary from 15.7-16mm)
Some sort of platform/piece of wood to screw the crane down to.
Glue
You could probably use a set of drill bits for cleaning up/boring out holes that might end up slightly undersized.

Assembly:
You will need 3 of each CrankSpoolPart1 and CranksSpoolPart2.
You will need 2 of TrolleyBolt.
Parts that have simliar names go together.
"Trolley.stl" will have following parts installed into it: "TrolleyRoller.stl," "TrolleyPin.stl," "TrolleyPinRetainer.stl."
The parts listed as "retainer" are just glued on the ends to keep it all together.

CrankSpoolPart1.stl and CrankSpoolPart2 snap together to make the spools that hold the string. Make sure that the holes line up when putting them together.

The "CraneJibHold.stl" sits in "CraneCap.stl" which sits in "CraneTop.stl."
1/4in tubes will only fit in one side of the printed part.
Anything that you don't want to move gets a screw through the provided hole.

Tension the string:
You can tension the trolley string a couple of ways. You can tie all of your string on while leaving the horizontal beams mostly/partially extended and then just tap them out the rest of the way until everything is tight. I also altered the trolley with threads and a bolt so the tension can be set by hand.

Notes: "CraneJibHold.stl" REQUIRES support touching the build plate.
Part "CraneCap.stl" should be flipped upside down and printed on its top.

In the pictures I use excessively long tubing to guide the string. You could certainly use shorter tubing and route everything through the body.

The pictures contain some parts that were from previous versions. The dimensions of the parts are small enough to be printed on just about any printer as the base and top are only 106mm x 106mm.

The CraneTop has a gear profile as I would like to add one additional crank handle and a gear to turn it...at some point.

12/18/2018: I changed the design of the trolley to include threads for two bolts. This allows the string to be tightened by hand very easily. The TrolleyBolt.stl is hollow so you can slip the string right through and out the side hole. The bolt came from Thingiverse file "Nut Job" by mike_mattala.

12/18/2018: String spools where enlarged and divided into two parts. StringSpoolPart1.stl and StingSpoolPart2.stl. This allows for thicker string.