Ok so this is a mash up between two different thingiverse listings:
https://www.thingiverse.com/thing:2011148
So When I saw this one I thought that's Nice but then I need a specific Metric Z-rod and a threaded Collar that I can only buy from a bot shop at premium prices. I saw a complaint on the printrbot site about their metric Z-upgrade that the Z - Axis falls down on itself and needs constant power on the motor to stop this so I thought that's not a good upgrade! .... thirdly I intend to increase my z volume to around 300mm if possible ( not sure it can handle that height but I'll try anyway)
and then I saw this thing for the original Printrbot simple
https://www.thingiverse.com/thing:96737
This seemed like the better option! A precision thread more specifically M5 0.8mm pitch that's available from most decent Nut and Bolt Stores! ( they sell this by the meter for half the price you'd pay for a 200mm metric z-rod ) and with the fine pitch, it stays put! ......... so I proceeded to draw an adaptor based on thing 2011148. I made a square adaptor that takes two brass nuts, they press fit from the side that mounts against the plate ( turns out two require more force than the Printrboard can deliver so I threw one out and only use one. I made no provision for a backlash spring or such because I don't think it's necessary since the thread has the weight of the z-axis on it.
watch the assembly ( I left no hole on the adaptor to facilitate tightening the grub screw on the GT2 belt pulley for the Y- axis motor) So before inserting the threaded rod, test fit the adaptor and the motor..... add the pulley, mark where it needs to be then remove the motor, tighten the pulley in place, add some loctite to the grub screws and then assemble the Y -axis. Insert the threaded rod last ( if you don't you wont get the pulley past the the threaded rod and wont be able to seat the motor correctly! )
you'll need to adjust the printer's firmware so that the steps-per-mm matches the new thread. To do this, connect to the printer with your software of choice. In the GCode input field type M501 ( this will read all your printers eeprom settings ) Copy and paste this to a notepad or wordpad page for safe keeping. Now Type M92 4000 ( the new value for the replaced z-rod ) after that type M500. Finally Type M501 to read it back and check that the M92 Command is now 4000. After that it should be ready to print.
This does work, it is a significantly worthwhile upgrade, my extruder nozzle no longer crashes into previously printed layers and there is no banding in the z - axis even at a resolution of 0.2mm
Consult both things that I listed here for additional setup info
If you modify the adaptor, share your mods here on thingiverse
Enjoy