Improving Bed Rigidity

The manual bed level/height adjustment system on the Ender 3 is very typical: the bed is suspended on 4 pairs of springs and long fasteners (one pair at each corner). This system is barely usable and a real nuisance to adjust. Moreover, suspending the bed at the ends of 4 long and narrow cantilevers is a problematic mechanical design at best; such a design has more lateral "slop" in it than it should—given the precision required to produce a high quality print. 

While working toward improving the bed leveling procedure, I realized that do "do it right" I needed to improve the rigidty of the bed first of all. The solution I implemented is simple and inexpensive, and makes the bed much more rigid relative to lateral motion in both the X and Y directions.

I replaced the springs with combination of steel and neoprene washers stacked approximately 12 mm thick.

This system increased the effective diameter of the supports from 4 mm (the M4 fastener) to ~11 mm, with a corresponding increase in lateral rigidity. Of course, you still need the vertical adjustment, which is the purpose of the neoprene washers. Because the Y carriage plate is relatively planar already, you actually don't need much vertical adjustment: 1 mm - 1.5 mm is really more than enough if you've properly squared the printer frame first.

Moreover, the neoprene is "stiffer" than the springs which, IMO, is an improvement. These, coupled with the bed leveling mods and improved procedures, have proven to be stable and precisely adjustable.

Here are photos of the front left and front right supports; the right rear is identical. The left rear stack is slightly shorter (remove steel washers as needed) due to the fact that the end of the cable chain mounts on it.

One last note: another factor needed to increase rigidity is to reduce the length of the cantilever. You can see that approximately 6 mm of fastener is exposed below the adjusting knob; this has proven to be a pretty good compromise for adjustability and bed elevation.

 

left front support
right front support