Quote Originally Posted by wingnut1000 View Post
When the print starts, it is printing about 20mm off the print bed in the air. I cannot find a way to resolve this.
I had some odd offsets too so here is what I did.

1. Use G28 to 'Home' before autoleveling starts. The probe should extend, go down, touch the glass, tap it again and then move the head up where it will stop.
2. I then connect to the printer with Pronterface and use the 'Z' controls to move the head down manually to a piece of paper. I hit the '-1' button until it get really close and count them. Then I hit the '-.1' button and count those. Each time as I get closer I tug on the paper until it has a little drag. In my experiment I counted 7.4.
3. Put that number you just got into the following line as a negative number:

#define Z_PROBE_OFFSET_FROM_EXTRUDER -7.4

4. Upload that to Ramps
5. Do another G28 to 'Home'
6. Issue a 'G1 Z0' . This should send the head to the glass and leave that tiny "paper thickness" gap. Have your hand on the power switch in case the head goes too far. Now you'll have an idea of the offset.

My first test still left the gap too big so I increased the 7.5 number I counted up by .05. Now the line for me is: (yours will be different...don't use mine)

#define Z_PROBE_OFFSET_FROM_EXTRUDER -7.45

That gave me the perfect gap the next time I did 'G28' followed by 'G1 Z0' . Since then I've been getting perfect 1st layers.

Maybe this will work for you too.