Make your large build plate level with this wedge jack!
With my CR10-S4 I found out that the large 400x400mm build plate was sagging noticeably in the middle. While there are adjustment screws on the four corners there is no way to support the middle of the build plate; this is what this part is for. Once assembled you can slide this in between your build plate and the lower support/mounting plate. Create support for the middle of the build plate and raise it using this W-Jack until level with the four corners by turning the screw. Note that this part is designed to be used in conjunction with a 3mm cork pad between it and the hot print bed.
Tip#1 Don't place the wedgejack directly under the temperature sensor on your heated bed otherwise you might damage it.
Tip#2 Use a long (7" or more), fine screw driver to easily reach the wedge jack from the edge of the plate when adjusting it.
Bonus Tip: This device is designed to have 4 mm of overall vertical travel controlled by 20 mm of horizontal movement, giving you very fine control when leveling the sag out of the build plate. With the screw I used it works out to about 0.285 mm of vertical travel for each full turn of the screw.
You can scale this to your needs but remember to scale evenly in all three dimensions
Use a bolt and nut of appropriate size when assembling. With default dimensions this is assembled with a 50mm long, 3.35 mm wide bolt.