In this article I’ll go over a few things I learned while setting up a Prusa style 3D printer, probably a lot of stuff will relate to other printers as well.
Once you have your printer built (if it was a kit) and running, the first and perhaps most important thing to do is to get the printing plate level and set the height of the nozzle above the plate. To begin, check that the X axis rails are level using a spirit level or simply measuring the distance of the rail to a datum on each side such as the surface it is mounted on or the top of the stepper motors. To adjust, disable the motors and turn one of the motors to raise or lower that side.
Now we can level the plate. The plate on my printer did not come with springs in each corner, rather it was just bolted to the carrier frame so it had no adjustment other than the X axis adjustment above and the Z axis stop switch position. The stop switch is secured via a bracket with two allen key screws on the outside of the left support. This works fine but is a bind to adjust, especially when trying to make very small changes. I considered designing a new bracket with a screw to adjust the position of the switch but instead installed springs at each corner of the plate to provide level adjustments as well.
If you will be using tape for better print adhesion, you should apply the tape to the plate. Next take a piece of regular paper and place it on the plate. Raise the nozzle a few millimeters in the Z direction and then position it over the centre of the plate. The interface on my printer does not allow you to easily home just the Z axis, so I connect it up to a computer running Pronterface that can home each axis independently. Home (or zero) the Z axis and then adjust the stop switch position such that you can feel the nozzle dragging on the paper when you move it without grabbing it.
Once you have the nozzle height set over the middle (and assuming you have an adjustable plate), you can then raise the nozzle and position it towards the four corners of the plate, I generally position it about 40mm away from each edge of the print area. Then home the z axis and adjust the screws in each corner of the plate to get it level. I found that if I wasn’t careful the adjustment would start to load and deform the carrier, in this case I would start again and then adjust two screws at a time to raise and lower the side of the plate rather than the corner. One thing to be aware of here is that the plate may not be totally flat; my plate for example has a bit of curvature such that the middle is slightly higher than each end in the y axis. It can take a bit of time but you just need to keep moving the nozzle and homing the z axis at a few positions on the plate until you have a uniform gap between the plate and the nozzle over the printer area that is as close as possible without grabbing the paper.
It’s a good idea to check the nozzle height and plate level fairly regularly, some printers with built in plate leveling will do a check before each print but I feel this is a bit excessive and would have masked another problem I ran into – the wing nuts on the adjust screws coming loose. Since I had installed springs under each screw, I thought that would have loaded the wing nuts and stopped them from undoing due to vibration but I started noticing that I was often having to make small adjustments to the plate when starting a new print. Then as I was printing a cable clip that had a thin cross section, I noticed the wing nuts moving when the zig zag pattern of the infill was being printed. The plate was moving back and forth in small amounts and the nozzle was set a little high so that when the plate was adjusted to get the correct gap, there wasn’t a lot of load on the springs. To fix this I replaced the wing nuts with nylon lock nuts that hold great but are a bit of a bind to adjust.
With that fixed I carried on printing the cable clip but soon noticed that the plate had started to rattle and the vertical walls were not straight. It turned out that the vibration had also loosened the y belt holder attached to the bottom of the plate carrier. I decided to simply tighten these and if they came loose again I would apply some thread lock or more nylon nuts.
With the y belt holder secured, the belt was still quite loose so I found a model for a y belt tensioner and printed one. This worked a treat but I found that if the bolt that holds the bearing was tightened too much it would press the tensioner sides onto the bearing restricting the movement of the belt and making the stepper motor work harder than it needs to.