Summary

Add 47mm to Z-axis travel using existing acme lead screw with $5 in additional parts.

Instructions

VITAMINS:

1 36" 8mm polished rod (McMaster 88625K67) - buy extras for other projects ;)

TOOLS

Working CALIBRATED printer
6.5mm drill
Allen wrench for 3mm socket
Hacksaw or 3.5" die-grinder with cutting wheel
Heat gun or hair dryer

INSTRUCTIONS

NOTE - all prints were done by author using KISSlicer.

Print the part
Clean part by trimming any overhangs on the the nut end and by using the 6.5mm drill down the clearance hole in the center
Cut two 14" pieces from the rod. I used a 3.5" die grinder with a cutting wheel, hack saw should work. After cutting sand the ends to remove any burrs. The 14" length results in about 3" of excess rod above the bearings (and 1" above the top of the y carriage).
with the printer near home replace the existing rods with the new longer rods. In the dry winter air I was able to twist each one out and replace one at a time so that I did not have to lift the carriage off the top.
Run the printer to close to the top of the Z-axis.
While supporting the carriage remove the two screws holding in the acme nut
push the carriage down so the acme nut pops up. Unscrew the nut.
lift the carriage and set it on the end of the acme rod or prop up using one of the old rods
fit acme nut into part. Use heat gun/hair dryer to slightly warm part if it doesn't fit.
While watching wiring, life carriage high enough that slide in the part at an angle to the motor from the bottom with notch facing motor. I found that if I screwed the part on the acme screw first it doesn't fit.
turn rod to thread into nut. MANUALLY turn rod to drop to home position while checking that wires are not catching If the nut hits your motor-to-rod vinyl tub before reaching home you can lossen the screws at the top of the part to allow it to "sit above" the plywood.
In Repetitier edit printer settings -> printer shape and change Print Area Height to 160
In KissSlicer edit printer -> hardware and set bed size Z to 160

PrintrBot Simple Z-axis Extension