Hello all. And Happy Easter or Passover or whatever holiday you might be celebrating this weekend. I am working to get octopi up and running with power control and camera on all 4 of my printers so I can start and monitor prints from my job. For this I need the reliability on my machines to be as good as it possibly can be. One problem I sometimes have is a changing Z homed position. And sometimes even the print head crashing into the build plate. For me this is because I am weak on the G code and when I start a print my machines all warm the bed, then home, then heat the nozzle, then start the print. If I remove any plastic hanging from the nozzle before I start the print I am good every time. However, if there is any filament hanging from the nozzle it contacts the bed before the z sensor triggers. On its own this changes the Z position, But the big problem, the force multiplier that sends the print head crashing into the bed is my placement of the Z probe. Look at my GEEETech i3 printer..



Yes the specific configuration I am working with here is aluminum beds and npn inductive proximity switches, a very cheap touchless solution from ebay. But reliable. This problem is not limited to this style sensor. This is a Z probe thing and it applies to bltouch or any other z sensor mounted to the print head. From the above picture it is clearly obvious that I chose to mount the sensor tucked in as close to the nozzle as I could get it. In my mind this was the best possible location. The problem can better be seen from a side profile of the print head..



Because of the specific positioning of the nozzle in between the carriage and the z sensor if there should ever be anything hanging off the nozzle it turns the whole print head into a see saw and as the threaded rods drive the z axis down it pulls the z sensor away from the bed. Once this process starts there can be no self correction. No chance of the sensor triggering. Yes I can figure out how to make my printers warm the nozzle before homing the z. But even still I have identified a huge design flaw here.