Bed Leveling

Description

There are many variable inputs to your prints. One of the simplest things you can do, which many of us avoid, is to level your print bed. There are a few prerequisites that we must cover before moving on to leveling. Perhaps the answer to this is obvious, but as a newbie I really didn’t understand how important this was. Apart from having a level bed you also need to set the distance between the bed and your nozzle.

Essentially the nozzle needs to ‘squash’ the plastic against the bed. If you watch the first layer being printed each thread should end up wider than it does during the rest of the print. As a guide the nozzle should be a paper thickness above the bed. With a piece of paper between the nozzle and the bed you should feel the paper drag against the nozzle as you try to pull the paper out.

If you have the following symptoms then you probably need to level your bed.

  • The initial layer is not sticking to the bed.
  • The initial layer isn’t complete; parts of the print just don’t get laid down.
  • The head scrapes the bed in some spots (you probably worked this one out for yourself).
  • Plastic gathers around the head during printing of the first or second layer.
  • When printing the second layer the print head is picking up the first layer

These symptoms can also be caused by other problems. But leveling your print bed is the best and easiest spot to start. If you know other symptoms please add them.

Optional Materials

Before you start I strongly recommend looking at these two upgrades. The are simple and simply brilliant. Bed leveling is one of the things you are going to have to do on a periodic basis. I would seriously recommend adding the following two upgrades:

M3 Nuts on Bed Spring Screws

Adding M3 nuts to the bottom side of the heated bed plate to lock the vertical leveling screws to the plate so rocking and motion between the Y lower plate and the build plate is eliminated. To stiffen the print bed, tighten the nuts under the bed so that the support screws are absolutely perpendicular to the print bed surface. Nylon-backed nuts insure that the screw will remain set, but if those are not available, LockTite, paint, or nail polish will get the job done. If using these, allow time to set before moving on, as vibrations tend to loosen things up.

Bed leveling thumbscrews

These replace the nuts under the bed base that you use to adjust the bed level. With the thumbscrews you can adjust each corner of the bed with one finger (or thumb). I highly recommend one of these.

Prerequisites

  1. The print bed material should be absolutely flat.
  2. The Y-Axis smooth rods should be leveled to each other.
  3. The Y-Axis base plate should make firm contact against the smooth rods on all four contact points (PLA bushings in the case of Prusa). There should be no rocking when pressing the corners.
  4. The left and right Z ends should be leveled so they are equal distance from either the top of the frame or leveled an equal distance from the top of the Z stepper motors. See this video
  5. The X-Axis smooth rods should be level across the Y-Axis rods.
  6. The Z-Axis Opto/Mechanical switch and flag should be located on the motor side of the X-Axis carriage.
  7. A piece of Letter paper (or A4 if you from one of the more under-developed countries 😀 ).

I’ve used ordinary 3mm house hold glass on a Di3 hot bed and it works really well.
If you can meet at least some of these prerequisites, it will be better than nothing. Each will contribute significantly to improving the quality of your prints.

Process

The process of leveling is fairly straightforward, and does not require any fancy tools. It involves only six (6) easy steps:

  1. Stiffen the print bed support screws.
  2. Set adequate tension in four (4) springs.
  3. Set the tolerance.
  4. Level first diagonals.
  5. Level second diagonals.
  6. Secure hardware.
Set Spring Tension

This step will depend on if you are printing on the aluminum plate or if you have added a glass plate to your printer. Typically you want to compress the springs almost all the way but then back off a little so there is some give to allow for adjustment during the bed leveling or if the nozzle was to run down into the bed. If you have added glass you may find that you have to compress the springs all the way to keep from having the nozzle hit the glass bed when homing. There is a printable part that can be used to give the Z Endstop some more adjustment with the glass bed Adjustable Z Endstop Link.

If you have your bed set where you know the Z Endstop will hit before the nozzle hits the bed (or glass) you can skip to the next section, otherwise you should adjust the thumbscrews (or wing nuts) until the springs are all the way compressed. That way we know the nozzle will not crash into the bed.

Adjusting the Z-Axis Home Position

Either though the LCD or the Host software Home all the axis. After the Z axis homes the nozzle should be above the bed (glass plate or aluminum bed). If the nozzle is too high and there does not look like there will be enough adjustment in the springs and you are using the adjustable Z Endstop then you will need to adjust the endstop screw so that the screw will be shorter (screw it clockwise).

Tolerances

In addition to being level the distance between the hotend and the bed is important. If you are using a strongly flat bed, such as glass, you should be able to achieve a gap of 0.2 mm. For less flat surfaces your gap will need to be larger. A common method of setting the tolerance is to place a piece of paper onto the bed, so that you can still move the piece of paper, but there is a slight drag. As you go around the bed, adjusting the level, you should use a piece of paper to check the tolerance. This will get you close but it is also recommend to print your object with 3 or more skirts on the first layer and watch as it is being printed then make any fine adjustments to get the lines to be flat (without being too flat).

Leveling Diagonal 1

Disable the Stepper motors in the LCD menu or though the Host software so you can move the extruder and plate by hand.

The leveling order is Front-Left, Back-Right, Back-Left, Front-Right. We refer to the first pair as Diagonal 1. With the Z-Axis homed, and positioned over the Front-Left corner of the print bed, use the tension nut to adjust the height of the print bed. Using the piece of paper between the bed and the nozzle adjust the height until the nozzle touches the paper but you can still pull the paper out with a little bit of drag. Re-home the Z-Axis and checking that the paper still drags. Adjust the nut as needed until you can achieve drag without movement of the print bed.

Once you have set the front-left corner, repeat the process with the opposite diagonal corner in the back-right. Return to the front-left corner and verify that nothing has changed. On or two repetitions may be required.

Leveling Diagonal 2

The second diagonal is leveled in the same manner as the first, but starting in the back-left corner, and ending with the front-right. It may be that after completing the procedure to this point, you find that Diagonal 1 is no longer set. It will most likely be a small adjustment, and a second repetition of the leveling process will correct this in most cases.

Reference material from http://reprap.org/wiki/Leveling_the_Print_Bed Content is available under GNU Free Documentation License 1.2

Video Guide

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