Bed leveling issues

Dear friends!
With your amazing help, I was able to finally finish my first build of my 3D printer (single frame Prusa i3). But still, I have some troubles with the heated bed leveling... The situation is as follows:
When I was assembling the Z axis, I notice that it's not perfectly parallel. It's not so bad, it's moving pretty nice (I don't have any tools - only some rulers). The problem is not in this, nor in the fact that my Z axis motors are not on one height from the bottom of the frame. Also, my Z axis screws (M5) and nuts are not absolutely leveled (the differences are in sub millimeter sector - 0.2-0.5mm which is not so bad for the printer's work but this is the best result possible for me - with my caliper). My issues are in this, that I don't really have some reference to level my bed. My hot end have some plastic left from the extruder tests and I don't really know how to remove it to make flat surface for leveling the bed.
I made the "paper sheet test" a couple of times but with not so good results. For now, because I build my hot end's mount myself, I don't want to reassemble it to put a servo for auto bed leveling. And I'm really tired from tries, and tries, and tries...
My setup is with a heated bed, 4 springs, bolts and nuts and of course - a glass plate on top of it. I will be glad for some advice... Actually is it possible to print on the glass without the Kapton tape? I will add some tape but I'm only curious...
Best regards!

Heat your hot end to melt the filament left on it, put a piece of paper under the hot end then home it (hopefully you've set the bottom at the point where the paper will drag). Pull the paper from under the nozzle and it will drag off any plastic adhering to it and leave you with a nice flat surface to level your bed with.

It is possible to print on the glass surface without kapton, but you may have adherence problems and it is more difficult to clean. A lot of people ditch the kapton in favor of blue masking / painter's tape. Your prints will stick to the bed better and cleaning the glass is simply a matter of peeling off the used tape.

If you are going to use an acetone / abs slurry for getting your abs prints to adhere, or dilute pva glue for pla prints, putting a layer of kapton down first is a good idea to make the bead easier to clean.

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The bed leveling serves only one purpose: to get the first layer of your print to stick to the bed. The bed has to be level relative to the extruder nozzle at all points on the bed so that when the nozzle visits those places it will "press" the plastic onto the bed with equal pressure everywhere. That means you must move the extruder nozzle around the bed in order to check and level the bed. A generic leveling method that should work with any configuration of leveling screws is to pick a reference point on the bed close to one of the leveling screws and adjust the other screws to get the bed set the same near the other leveling screws. Once the bed seems to be adjusted for equal level near the leveling screws, move the nozzle to the center of the bed and set the zero adjust of the Z axis. Always level the bed and zero the Z-axis when both the bed and the extruder are at print temperatures. That way there won't be any hard little plastic bump on the end of the extruder and the bed will be warped in the way it normally warps at print temperature.

4 screws is a common configuration (don't ask me why), but if you recall your first geometry class, it only take 3 points to define a plane. My print bed is is supported at three points, only two of which are adjusted for leveling.



The screw at the back is fixed and the screws at the front and left are used to level the bed. The front and back screws are parallel to the Y axis and the screw on the left center of the bed tilts the bed around the Y axis. Leveling is accomplished by setting the nozzle down at the back Y screw position. Next you push the bed back so the nozzle is at the front screw position and adjust for the same height. Finally, move the bed to the left screw position or the right side of the bed opposite the left screw, and adjust for the same height. Adjusting the left screw does not affect the height of the center of the bed between the Y axis screws. Once the two screws are set, move the nozzle to the center of the bed and set the Z axis zero with a piece of paper or whatever. This system work well and doesn't require adjustment unless I change the extruder.

When you want to print a cube or a sphere or any other shape, the orthogonality of the axes determines whether you actually get a cube or sphere or whatever. If the axes are not orthogonal, your cube will be a rhomboid, your sphere some sort of ellipsoid. The bed leveling does not correct such problems. Orthogonality of axes can be checked by measuring the distance between diagonally opposite corners. If things are truly square, the distances measured will be exactly the same.

Edited 2 time(s). Last edit at 05/29/2014 10:11PM by the_digital_dentist.

Wow, thanks, guys!
Your advices are great and very helpful! I think that now I can do the correct leveling of my printer.
I checked the squareness of all of the axis and I was able to level them pretty good. Now I need to stick my kapton tape on my glass and do the vertical tolerances.
Thank you again!
Best regards,
Bobby