I am also having Z homing issues with the 12" that I put together 1-2 weeks ago. I have swapped the Z axis home switch around with one of the others and have everything mounted with screws. It is very frustrating to have to fight with the printer for 20 min to get the Z home position fixed every time I want to print something. I have been very close to throwing the damn thing in the trash because of it. I also have the Rumba board so I am not sure if there is an issue with the Rumba or something else but I would like to get it figured out so I can actually enjoy using the printer instead of fighting with it.

I am beginning to think the issue is with the type of switches sent with the kit. For some reason he included micro switches with roller ends on them instead of standard lever ends. If you are homing off of a flat surface the roller switch would be fine IMO but on the Z axis you are using the tiny bolt as the homing surface so I think there are some inconsistencies related to that because depending on what part of the roller radius the bolt hits on it changes the home position. I have some standard micro switches on order to swap out the roller switch with. I hope that fixes the issue because at this point in time I don't really want to even use the printer because of it.

Quote Originally Posted by tsteever View Post
Clips in the corners.

Thanks, I am still learning a lot about the code and really (if you can't tell) do not know what I am doing...yet.

I plan, was to manually set the Z axis myself cause every time I autohome the z axis is in a different spot. I am not exaggerating. Right now I have things tore apart for cleaning but my intention is to replace the Z endstop with a printed setup from thingiverse. Before tear down I hit autohome. The bed wend to the corner and the z descended to a level below the glass. Previously i had adjusted it to be a paper height from the glass.

My glass is clipped at the corners and the home is actually off the glass (in case of the nozzle going below glass level). When I hit home and the machine was at zero I moved the extruder over to verify that the nozzle was at "paper height". I then hit home again and this time it descended below the glass level by almost .6mm (estimate). I immediately hit home again without moving anything and the z went up and stopped. It never descended down again. This time the axis was .4 above the glass!