Auto home works in one spot not another

[Kevin Price]

Question for you all.  I finally took my printer out after receiving it 2 yrs ago...

Im finally trying to get it to set up and print but I am having a weird issue.

When I auto level it will check the front left no issue.  Then it goes to the back left and it smashed into the bed hard.  Then it travels to the right and gives it a small tap.

Why would it do that?  Shouldn't the sensor stop then check before it goes to far?

[Dante Ridolfi]

If the head comes down and the sensor behind the head is not over the metal bed, then the sensor will not trigger and the head will smash down and continue until the sensor sees enough metal or something breaks. 

IF the sensor is over the metal bed and is smashing hard in the rear, I would suspect the bed is NOT level and the back is higher than the front. In this case raise the front of the bed up and lower the back down some. 

I used a level to make sure the machine is as level as I could get it, THEN leveled the bed using the level. This helps a bunch but doesn't take in account for the X axis arm not being straight and level from the machine. If it isn't then the right side of the head could hit too soon on the far right or be too high. 

Basically is a game of balancing. I have also noticed that if your Y axis isn't tight enough your bed can wobble, this create an issue with printing as the head will "bounce" along the bed as it shakes. The head can also get loose on the X axis and that will create issues too. 

I have already replaced MOST of the black wheels on mine with a higher quality poly wheel you can source off Amazon or other 3D Printer sites.

Much luck with getting it up and running. There are so many "tricks" and "glitches" it would take me weeks and a book to go through them all with anyone with one of these printers. I have upgraded both the wheels and the fans on the print head, as they were substandard parts. Also watch that stepper motor for the Y axis (the one that drives the print bed back of forth) as it heats up really bad. Some people put a fan on it, or (like i did) put a heatsink from an old CPU on one side which helped it a bunch.

Happy Printing!!