Bed leveling woes.

I just made a few upgrades to my machine. I replaced the cheap plywood lower print bed with 1/4" MDF (much better -- the plywood was warped like crazy). I also added a 4th lm8uu bushing on the bed (I had to print another clamp since my plastic parts kit only had 3), installed printed bed leveling thumb screws, and I used 4 corners for leveling instead of 2 + 1 in the middle on the other side. Despite all this, I still can't seem to get the bed leveled properly. I can level the corners no problem, but when I move the carriage to the center the nozzle hits the glass. I have to move the z axis up by about 0.2 mm in order to make the paper sliding under the nozzle feel like the corners. If I flip the glass over there's no difference. It seems to bow outward a little no matter which way I put it. I've read that the center is where the leveling is the most important, so my plan is to get the corners to "feel" the same, then raise Z 1mm, move to center, home Z, then raise 0.2mm and move the endstop switch to make that my new home position. Does that sound like it would work or do I need to do something else to make the bed more flat? I'd rather have a consitant bed height, but I'm willing to go with whatever works.

Also, just an FYI here. When I move the motors too fast with the electronics connected, the LED on the main board lights up even if there is no power connected (no USB or 12v). I'm guessing that the motor is acting as a generator when I move it rapidly and supplying power to the controller board. I don't know if that's bad for the stepper drivers or not, but I'd keep it in mind.

Check your glass with a straight edge, if it is flat diagonally and side to side, you may have slightly bent X or Y smooth rods.

Edited 1 time(s). Last edit at 03/18/2013 10:37AM by Dirty Steve.

For starters, 3 point leveling is in many ways superior to 4 point. With 3 points your glass sheet MUST lie in a plane, but with four points you can bend the bed.

Secondly, a hot bed will be slightly non flat due to thermal expansion.

Thirdly, how are you clamping your glass down, it can be easy to clamp it in such a way that you bend the glass.

What machine is this? Thin x rods could cause the x carriage to sag in the middle.

Finally - could your cables or filament be pulling upwards slightly on the carriage when it is at either extreme of travel?


My machine is quite large causing the x axis to be lower in the middle through the rails bending slightly. Similar amount of difference, it seems quite possible to print with 0.1mm layers though over the whole bed none the less. The first layer is a bit more squished in the centre, and a bit tall at the edges, but it works perfectly well.

The LED illuminating WILL happen if you manually push the bed even with power disconnected. This is telling you that you are pumping a voltage into the Ramps boards LED? Obviously this is not desirable but I'm sure we all do it - just move it slow if you have to. I had a problem with bed leveling mainly because my PCB heat bed was warped. i overcame that by putting a dab of silicone in each corner of the PCB bed and then laying the glass in position- a slight gap of 0.1mm to 0.2mm should be present along the edges. (My glass can reach temp no problem). I would also strongly recommend, as mentioned by Konwiddak, to have 3 point leveling and would suggest buying a piece of 3mm aluminium for top and bottom plates.