The assembly of my AltMill went very well except for a couple of minor issues. If you assemble yours working off the SIENCI assembly video be sure to cross reference to the online written instructions…in particular when assembling the Y gantry plates note the 5mm x 20 socket head screws to be used on the ball screw nut…I used the 12mm as stated in the video and those don’t provide enough thread engagement on the ball screw nut.
The other issue I encountered was on the homing of the Z axis. My Z axis went right to the top of the carriage and crashed. After some examination I realized the Z limit sensor was not picking up the carriage during homing. I passed a piece of metal in front of the sensor to verify its operation…all was well there. The only thing left was the sensing distance being to far away as the sensor is supposed to pick up the ball screw nut when the carriage moves up. I followed the written instructions for the Z sensor installation and for me that did not allow the sensor to reach far enough into the carriage cavity. It is very difficult to see inside the carriage cavity when the axis is up towards the top, so what I ended up doing was to remove the sensor from the axis plate then move the carriage up by hand until I could see the ball screw nut through the sensor mounting hole. I then put the sensor back in the hole until it touched the ball screw nut, then spun the mounting nut down until it touched the mounting plate, then turned the nut down a little more for sensor clearance, then moved the Z axis back down by hand and replaced the front sensor nut. This worked great and was much easier than trying to guess when the sensor tip was even with the inside of the mounting plate surface…it also gives much more thread engagement for the front sensor nut.
I suppose there can be a difference in sensor sensitivity which may or may not have been my issue but if you find your Z axis crashing into the top of the assembly during homing, you may want to try this if your sensor appears to be working on its own.