FoX (ZX) 45mm Axis System - Anycubic I3 Mega or any (custom printer)

The Anycubic I3 Mega is an excellent entry level 3d printer. It has a rigid mainframe, a very good heat bed, decent electronics and a low acquisition price.
The main weak points are the unreliable hot-end assembly, the positioning of the heavy Bowden extruder attached to and way out from the center plane of the X-gantry, the sheet metal construction of the Z-carriages, week, wobbly and unable to correctly self constrain the geometry of the complete ZX axis, the lack of tensioning features for X and Y belts.

An uninspired design decision - to use a 50mm X-gantry system - has isolated the Anycubic I3 Mega from the i3 world of 3d printers, most of them built on 45mm X-gantry systems.

Any 3d printing passionate and ambitious Ai3M user, once has passed the 3d printing childhood period, might feel the need to completely revise this printer or to move to another 'higher level" 3d printer. Two possible options are: paying at least three times the cost of an Ai3M and getting a printer that might still need upgrades, tinkering and care - or paying much less and turning the Ai3M into a machine that can finally offer excellent printing quality in a package with fun, enjoyment, a bit of challenges and a lot of satisfaction.

The 45mm Ai3M "FoX" ZX axis design is developed for those users that would prefer the second option and have the strength and the skills to engage in a relatively complex modification. The design intends to solve most of the mentioned Ai3M mechanical problems and returns the printer into the 45mm X-gantry i3 family, opening the large world of dedicated i3 solutions.

This design is derived from the Ai3M 50mm FoX X-gantry system:

https://www.thingiverse.com/thing:4352064

Anyone really interested should read and the information provided there.

What is different:
-The 45mm gantry system returns to the "original Prusa" i3 large family of printers based on 45mm X-gantry systems and consequently all the X-carriages and extruders developed within this concept can be used.
-The design provides a complete ZX kinematic system, that includes a 45mm X-carriage fully adapted for Ai3M. The X-carriage is developed from Prusa MK3 R2 X-carriage, having "standard" Prusa interface attachment points. It changes the Prusa curious cable support to a decent cable chain attachment and adds a provisioning for the Ai3M hot end PCB.
-The design includes optional top Z axis guiding fittings (4 ball bearings 8x16x5mm required, I used something abbreviated 688 RS 8x16x5). Optional fittings - but highly recommended for the best printing quality :)
-Minor evolution and refinement of the 50mm design.

I decided to test this design using one of the best direct drive extruders available in the 45mm world - the Bondtech MK2-MK3 (full kit) upgraded extruder made for Prusa:
https://www.bondtech.se/en/product/prusa-i3-mk2-mk2s-extruder-upgrade/

A few words about my experience with this extruder:
-I was surprised to see the complete Bondtech X-carriage assembly having almost the same weight as my E3D Hemera X-carriage! - it looks way more massive!
-After some quick tuning and 25h+ of printing I can say I feel this extruder accurate and reliable. I like how the (automatic) filament loading - unloading works, smooth and precise - it made me think to a future upgrade - Ai3M + Prusa's MMU (multi-material unit).
-After another 25h of printing: Bondtech had to follow the Prusa extruder architecture, with the stepper motor in front of the extruder, instead of a side placement, closer to the ZX axis. In this configuration the center of gravity of the extruder assembly is ca. 40mm away from ZX axis mid-plane, in a high Z position. A "perfect" system to work as a mechanical amplifier for any micro-vibrations in the ZX axis. The linear guiding constrainment on the X axis has to be perfect and the X accelerations need to be reduced in order ot achieve very good printing quality.
-Vref set to 2,5V - the motor gets quite hot during printing. I would say 60°-70°C, close to the max defined operational temperature 80°C. This extruder working in an enclosure might not be quite happy...

• FINAL EDIT:
  The last minor design evolution and refinements, as well as the complete CAD data, 2d drawing and hi-res pictures are saved in:
  https://github.com/Sergiu-I/AI3M---FoX-45mm-ZX-Axis/tree/CAD-models
  If opening a step file and saving the required models as STL files sounds unfamiliar or is too much trouble, the included models are very good too - they are fully tested and satisfactory working.

And finally:

Why "FoX"? - because the FoX has outsmarted the Bear :)