Inspired by Balua's brilliant design https://www.thingiverse.com/thing:268091 but different solution: Just roll the tape in and out of the 3D-printed spools. This way the tapes do not have to be cut and bared in the middle (no corrosion risk). 

By collapsing the tapes into the spools (starting at the outmost director) you can reduce the directivity of the antenna (and its gain) without disassembling anything. Build a highly directing antenna (with many directors) and choose the effective directivity in the field.

I added .stl files for a square 20 mm wide boom, 16 mm (flat-pressed) measuring tape and 1, 3 and 5 screws plus a bracket for a vertical PCB soldering type SMA connector.

If you are using a different boom form (e.g. circular) or boom width or measuring tape width, then you will have to produce your own .stl files from the enclosed OpenSCAD source file after having amended the parameter values at the top of the file or the boom form further down in the "boom_cutout()" module. 

But with OpenSCAD this is easy enough:

• Measure the tape width (flat-pressed).
• Download and install openscad from https://www.openscad.org
• Launch OpenSCAD.
• Open the downloaded YYMMDD_yagi.scad source file (File/Open).
• Amend the parameters at the top of the source file with the built-in text editor and save your file under a new name (File/Save As).
• Render (Design/Render).
• Export as .stl (File/Export/Export as STL).
• Slice and print.

I printed it in PLA at 0.3 mm layer height, 0.5 mm extrusion width, 15% infill, 3 peripherals and 3 top/bottom layers. No supports required.

See my other designs at
https://www.thingiverse.com/thinger13/designs