Tips #5 - Alignment 101 on a 3D Printer

After I purchased my Hictop Prusa i3 Clone four years ago, I went through a very trying time attempting to discover what things were going wrong with the printer.  It seemed like I got excellent prints, then there was a disaster, something out of kilter, or even an indication that squares weren't square anymore.  The more I fiddled, the more I discovered some unwritten rules of keeping a 3D printer up to date, at least in alignments.  So here are some tips for making better use of time between issues that arise (note that these items are for Reprap style printers, like the Prusa i3, but the principles are the same with most printers):

Assumptions:

1. Get used to the idea that you will have to re-align the printer every so many prints, even with an auto-leveler
2. Over time the correction adjusters will come loose because of shaking and general acceleration of parts
3. The same shaking will cause corners and cams to come loose
4. Belts do not stay perpetually tight
5. Mechanical stuff will wear out and will need replacing

Rules:

1. Make sure the printer is off, it makes it easier to move things around without having to disable the stepper motors.
2. Start by making sure that all of your 3D printer corners are exactly square.  You may think that you have a 90 degree corner but unless it is measured to be 90 degrees, it is not.  If the corners are not aligned, you will not see a rectangle on prints, you will see a rhomboid, and if it is really bad a trapezoid.
3. First and foremost after squaring the printer, make sure that all bolts are tightened on the printer
4. Make sure that all belts are tight and that the cams are on the stepper motors correctly (usually by having the set screw on the flat portion of the spindle); make sure all cam set screws are tight.
5. Check the movement of the belts as they are moved back and forth.  What you are looking for here is making sure that the belt moves easily without binding, or rubbing on anything; especially important for the X and Y axis belts.
6. Clamp the printer structure to its surface to prevent shaking that might cause the printer to move from its location.
7. Now we start aligning stuff.  Start by making sure the printer structure itself is level in the XY plane, use a level - I prefer a magnetic level and sometimes use a circular level.  You would be surprised to find that most surfaces are not level.  Sometimes some wooden shims are needed to get it level on a table or bench surface.
8. Once the structure is level, level the print bed (moves in the Y axis direction) using the adjustment screws on all four corners.  You need to have it level from corner to corner and diagonally.  I like to start in the middle of the bed checking diagonal level in both diagonals.
9. Apply blue tape if you use it to the bed.
10. Next, check the level of the X axis beam on the metal rods that the print head travels on.  If the metal rod is not level you will need to adjust the Z axis couplers on one side or the other to bring it into a level condition.  If the printer had been on you would need to unlock the stepper motors to do this.
11. Next, check the distance of the print head from the bed by adjusting the Z axis couplers on either side of the bed to bring it up or down as necessary.  I generally find that the width of a separation tool is enough, others like the width of a piece of paper.
12. Recheck the X axis level after changing the Z axis couplers.
13. Turn on the printer.
14. Adjust the auto-leveler so that it just comes on with the present settings.
15. Attempt an auto home. Recheck the distance of the print head from the bed.  If adjustment is needed, unlock the stepper motors prior to moving the Z axis couplers and readjust auto-leveler as per #11 and #14.  Repeat until the distance of the print head is acceptable.
16. At this point you are as aligned as you can be mechanically.
17. To help keep alignment, consider lowering the maximum acceleration level and the xy jerk value; this will also serve to lower the shaking and “walking” that most printers tend to have.
18. Higher temperatures will add to misalignment due to expansion of metal parts.  So recheck alignment of the bed after a high temperature print.