The stock heated bed on the Monoprice Maker Select v2.1 (and probably other Wanhao i3 variants) very easily slides around a mm or two in each direction in relation to the Y carriage plate. This causes noticeable layer shifts in the X and Y axis from the slightest bump to the heated bed during printing.
These heated bed stabilizers "hug" the bed screws to prevent them from wiggling around in the larger carriage plate holes. The springs and thumbscrews act together to squeeze the stabilizers in a sandwich against the carriage plate, providing enough friction to keep the screws from shifting along the X and Y axis.
This Thing is part of a set of mods I've designed for this printer - here's the rest of the set, I hope you find them useful:
Monoprice Maker Select v2.1
Items to print:
Qty. 4 - bed_stabilizer_top
Qty. 4 - bed_stabilizer_bottom
You need one top and one bottom for each corner.
To assemble, you'll need to remove the all the thumbscrews from the heated bed and lift up each corner (you don't have to completely remove the heated bed from the carriage plate).
You then want to create a sandwich at each corner, like this:
Top printed part
Aluminum y-carriage plate
Bottom printed part
After you reassemble all the corners, it's very important to fully compress and release all four corners of the heated bed repeatedly until the corners travel relatively smoothly within the limits of the springs and thumbscrews. The idea is to loosen up the holes in the printed parts just enough to permit the bed to move if the extruder pushes against it due to a Z-axis problem.
I was trying to successfully print four y-axis bearing brackets (http://www.thingiverse.com/thing:1375534) and just could not get a set to print without layer shifts of some kind that would have thrown off the bearing bracket alignment. This led me to try and track down why.
As it turns out, I print exclusively in PETG, which means I get occasional large blobs, particularly on infill (still working on tweaking slicer settings). When the print head bumped these blobs it would shift the entire heated bed in relation to the Y carriage, causing these layer shifts. I developed this mod to fix this problem.
Note that I originally designed this mod with the intention of supergluing the top and bottom halves together, creating a nice extra squeeze against the carriage plate. After doing a test fit, though, it solved the problem without the extra step of gluing it, so that's how I've published it.
Source file from DesignSpark Mechanical (.rsdoc) is included in the file list.