A popular modification to the Monoprice Maker Select (Wanhao Duplicator i3) is a “Z-brace”. A diagonal structure that braces the horizontal Y-axis carriage to the vertical Z-axis frame. Playing with my own printer, I can confirm that the Z-axis can be noticeably flexed by hand, and that a similar printer with the Z-brace modification does feel noticeably more rigid.
But the printer isn’t actually printing under the strain of a human hand pushing it around. It only needs to withstand the stresses or a print, which does not actually apply force in the direction where it is weak. So that leads to the question: how much difference does chassis flex actually affect a print in progress?
I had a chance to quantify this behavior, borrowing a dial indicator that is used to precisely dial in machine tools. It is completely overkill for this purpose but it was fun to get some data to back up (or refute) internet wisdom. I told the printer to work on my hash-shaped test file that makes a lot of sharp right turns, and measured chassis movement through these turns.
Close-up while printing:
Verdict: Z-axis chassis flex is real. It is definitely moving by a measurable amount when performing a 3D print. That said, the amount of movement is very small compared to all the other factors affecting dimensional accuracy and not a major factor in print quality. I’ll prioritize fixing other problems with the printer before I worry about installing a Z-brace.