Some FDM printers (like the Prusa i3, and others), whether purchased assembled or as a kit, are already equiped with some auto-leveling feature, that means an automatic leveling of the nozzle relative to the printbed, in a way that the distance between both are always the same – and as little as possible. On the other hand, there are other 3D printers / kits that doesn’t have such feature. In this cases, it’s necessary to use the endstops (micro-switches that limit the axis movement) and, for fine-adjustment, screws / springs that change the height of the printbed.
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The Graber i3 is a 3D Printer Prusa i3 clone, but with a laser cut MDF structure. There are lots of Graber i3 kits, a little bit different from each other, but the majority is based on the same MDF structure, provided on this GitHub project. It’s a good project, to be honest, it’s ver stiff and easy to assemble.

A problem that had not occurred to me though – in fact, I didn’t notice it for months – is that MDF wood expands/shrinks depending on the heat difference. For the most part of the MDF structure, this is not a big deal. But the printing bed, for ABS printing is heated up to 100C and it is bolted to the MDF base, thin and almost fragile. After some time, I noticed that the heat from the printbed made the MDF base to curve down. The consequence is that the base was colliding against the zipties that hold the Y axis rods and endstops. This collision was enough to make a difference on the printber height (relative to the nozzle) and propagate as object imperfections.
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