My new 6040 improvement plan.

[hanermo2]

Excellent thread !
I very much like the OPs grit-n-go attitude, esp. considering actual measurements re_ flex.

Very Well Done ! keep at it.

The major value to the OP is learning about rigidity, motion control components and actual needs of machine tools in cutting apps.

All others reading this may learn a lot about what is flexible and or sloppy (backlash, jitter, bend aka flex) in these machines, and by about how much, and what happens when you change one part at a time.

The vast majority of people do not ever measure stuff like the OP did re:flex.
The vast majority also give up, usually soon.

I am not giving advice here ... (tend to do too much of that..).

There is a big body of evidence that more or less all machines will do upto about 5x or 500% "better" with some tune-up, mods, and very carefully controlled cutting parameters- for a single specific tuned job when optimised for the machine and tools available.

This applies to the chinese 6040s, bridgeports, small lathes, big lathes.

[Zeeflyboy]

]very carefully controlled cutting parameters

That part is the most significant by far imo... I've always said the most productive "mod" I ever did for the X2200L was learning to use Fusion360 and figuring out how to best use/tweak adaptive machining for my machine.