I have found that the z-stop adjustment screw on the Monoprice Maker Ultimate does not have a lock nut and can easily come out of adjustment. Also, this screw needs to be adjusted any time the bed is leveled, nozzle is changed, or printing surface is modified. To make the process easier I have designed a knob and thumbwheel nut holder to attach to the M3 adjustment screw.
M3 x 30mm socket cap screw
The model files are dimensioned for a very tight fit against the nut and screw threads. Scale the model in the slicer software to compensate for printer tolerances. Press the nut into the thumbwheel with a pliers or vice and drive in the screw to fully seat it. Drive the screw into the knob to tap threads then remove it.
Install the thumbwheel on the screw so the opening faces the screw head and install into the printer bed. Install the knob onto the screw threads from the bottom of the bed. It should be tight enough to require a pliers to hold the knob while driving the screw with an allen wrench until it bottom outs.
The Maker Ultimate needs to have the z-stop adjustment screw adjusted any time the distance between the build surface and nozzle is altered (bed leveling, nozzle change, build surface change, etc.). With the printer off and nozzle at ROOM TEMPERATURE, adjust the z-axis screw rod by hand to raise the build surface to the nozzle. I set the gap to 0.06mm with the thinnest feeler gauge in my set with good results.
After the nozzle gap is set, adjust the z-stop adjustment screw just until you hear the limit switch close--no further. Lock the screw into position with the nut thumbwheel. The printer is ready to use.
Scale dimensions in slicer to compensate for dimensional tolerances
The screw knob model contains M3 threads but it is not critical for this detail to show up in the print. Threads will be tapped when driving the screw in.