I have had my Prusa i3 V2 for several weeks now and after a very frustrating initial week I finally got to the point where I could print reliably. I thought I would pass on my thoughts and what I did to make the printer work reliably.
First of all I found the process of manually leveling the print bed to be a major PITA! I realized after several days of struggle that the desk I placed the printer on was not consistently level across it's surface and this allowed the printer to flex a bit and cause the bed to change as things moved. I resolved this issue by cutting a 3/4" piece of Oak plywood to 16" x 18" and mounting the printer on the Oak. If I were to cut another piece of Oak for the base I would make it 18" x 18" to allow sides to be installed if desired; I don't care about enclosing the printer so my 16" x 18" works fine. I verified, before mounting the printer, that the surface of the Oak plywood was level and square across the surface. I picked 3/4" Oak plywood because it is strong and rarely do you find one that is warped. I set the printer on the base and used four 1/2" conduit clamps to secure the lower threaded rods at each end to the board. I used a square to verify the acrylic frame was square and firmly seated. Once this was done the printer no longer flexes print bed doesn't move except on the springs.
Over time I found I that I need to re-level the print bed fairly often. I decided to check the level of the X Axis rods, which I thought were set properly per the build manual, and found that they were not equal on both ends which explained why my bed springs were compressed more on one side than the other. I got a 1.5" x .5" piece of Poplar wood and cut a 125 mm length to use as a physical calibration tool and verified it was square. I then raised the Z axis until I could get the wood under the lower X Axis chrome rod. I then lowered the Z Axis, carefully, until the lower chrome X Axis rod was just touching the calibration tool. I could still remove the tool but I could feel some drag as I did. I then move the tool to the other end of the lower X Axis chrome rod (left side) and found that this side was quite a bit lower than the X Stop side (right side). I manually turned the left Z Axis stepper motor until the chrome rod was at the same height as the calibration too. I then verified that the right side was still at the same level. Now the X Axis is level with reference to the Oak plywood base and therefore properly balanced between both ends.
I then cut another calibration tool out of Poplar 1.5" x .5" wood to 69 mm. I selected 69 mm because it allowed me to calibrate all four corners of the underside of the print bed and keep plenty spring left to insure the bed was under a bit of tension with the springs but not overly compressing the springs. I used this tool at all four corners (near the corners actually) and adjusted the springs so that there just a slight bit of drag and I moved the calibration tool in and out from under the print bed. Once this was done I was confident that the bed was level relative to the Oak plywood base.
Now I used the adjustment screw for the Z Axis stop to bring the nozzle to about the distance of two layers of A4 paper and could feel drag at the home corner. I then lifted and moved the nozzle to each of the other three corners and performed a Z axis home using the paper to check the distance and all four corners were so close to being the same that (just a slight drag difference on one corner) that I did not make any other adjustments.
Now before I print I just check the bed height with the calibration tool and make sure the Z Axis home is correct. This works only if you absolutely know the printer is sitting square on the surface. My prints have been working very well since I set things up this way.
I have attached pictures of the printer mounting and the calibration tools in use.
I hope this is of some help to others and I know there are other things that can be done - I plan to replace my Z Stop switch with a light chopper that will be plug compatible but that is for another time.
Simba
