It has been on my mind for quite a while to do a 2020 alu extrusion based Cantilever 3D printer, and so I started in December 2020 with a rough design, starting from the existing Ashtar K design and cut away parts:
- using Head XZ and Bed Y
- aiming common build volume (e.g. easy to source print bed)
- 140mm to 190mm each axis
- tried 6, 7 and 9 beams options, settling with 6 beams for now
- aiming for uni-length 2020 alu extrusions, T-slot and V-slot where a carriage rides (X & Z axis) with V wheels.
- trying to keep as simple as possible
20×20 aka 2020 Alu Extrusion T-Slot Profile 
2020 V-Slot Profile 
V wheel
Frame: 6 vs 7 vs 9 beams
6 beams 
7 beams (+1 back) 
9 beams (+2 left + right)
The 9 beams give an overall better sturdiness, but not sure how essential at small building volume (less than 220mm each axis). I might be able to remove beam, the last beam at the back at the bottom reducing to only 6 beams, in that case the Y motor is mounted on the remaining beam in the back.
Z Carriage: 3 vs 4 wheels module
3 Wheels / 2 Mounts 
4 Wheels / 3 Mounts 
4 Wheels / 3-wide Mount 
4 Wheels / 3-wide Mount, Routing Inside
The 4 wheels looks best but it also sacrifices some of the X range by apprx. 10mm, the obvious choice is 3-wide mount – actual tests will tell if the X & Z axis are solid enough.
Different Sizes
Ashtar B 150x150x150 
Ashtar B 180x180x180 
Ashtar B 200x200x200
The 200mm build axis length would be good, but I’m not sure if the XZ carriage will allow it as the max margin or tolerance would be half of a layer-height, e.g. 1mm layer height ⇒ 0.05mm tolerance, at X = 0 .. max the head should not flex more than 0.05mm. At this this early draft stage I don’t know which size is most suitable, I focus on 180mm build axis.
The project page on Ashtar B summarizes the current state.
