In April 2020 Jon Schone (@properprinting) showed a “Moving Portal” mod for his CR-10 – a Prusa i3 derivative – and I thought to adapt his approach as “Ashtar M” as moving XZ frame or moving gantry in CNC terms.
On a second thought, this approach makes only sense with larger beds, as the bed weight should exceed the weight of XZ frame and X carriage:
weight(XZ frame + X carriage) < weight(bed)
and as I compose my Ashtar 3D printer series with alu extrusions (beams) I can say:
weight(XZ frame) = beam X * 2 + beam Z * 2 + NEMA17 * 2 weight(bed) = X * Y
and it becomes here clear, the bed weight grows X * Y whereas XZ frame only (X + Z) * 2, but also 2* NEMA17 motors of the Z axis are part of the XZ frame.
Moving Portal / Gantry
A few still images of Jon’s YT video to look at some details of his approach:
Jon Schone: Moving Portal Mod
Z motor sits inside the Y carriage (40×20 V alu extrusion)
Y belt end
Single Y motor, 8mm rod to drive two Y belts
XZ frame Y Mount
Moving Portal / XZ Frame
First Draft
using solely 500mm 2020 alu extrusions (T-slot for general frame and XZ frame, V-slot for carriages: X beam, 2x Y beams)
trying to achieve 400x400x400mm build volume as close as possible, alike Ashtar C 38.40.36
T-Slot 2020
V-Slot 2020
V wheel
Using for Y carriages existing vcarriage2 module with vcarriage2(width=100) to have it wide enough:
Bare view on Y carriage with XZ frame
Adding side pieces “A” & “B”
Piece “A” connecting Y carriage with XZ frame
Piece “B” connecting Y carriage with XZ frame
Piece “B” bottom view
At position 0,0,0
The two main new pieces required were connecting the Y carriage with the XZ frame:
Piece “A” outside ycarriage_xzframe_mount_a(): has to be printed with 0.1mm layer height in order to stay within the +/- 0.05mm tolerance, otherwise it will introduce tilt and stress on the Y carriage and cause long term damage – tricky part to print.
Adding side pieces “A” & “B”
Piece “B” inside ycarriage_xzframe_mount_b(): is quite elaborate already and should be functional, with the Y belt ends fastening with M3 screws and M3 nuts inserts, the belt endings will come out downward:
XZ Arch Option – Removing Lower X Beam
In order to gain some Z build space by lowering the print bed, I may reduce the XZ frame to an XZ arch:
Side pieces “A” & “B” with Arch (lower X-beam removed)
Side piece “B”
Actual physical tests may reveal if it’s suitable to maintain overall geometrical integrity. Removing the lower X beam also reduces moving mass of the XZ arch/frame/gantry.
Pros
gain Z build space
reduce XZ gantry weight / inertia
Cons
decrease XZ gantry stability
Further Development
As I develop Ashtar M further, I will post updates on the blog here, and also keep documenting the current state at Ashtar M page.
2021/01/07: Y motor and shaft extension with Y pulley holder added
2021/01/03: Z motor mounts added, Y carriage to XZ frame/arch pieces refined using rcube()
2020/12/19: new “XZ Arch” option (removing lower X beam from XZ frame)
2020/12/17: change X carriage, routing X belt inside 2020 alu extrusion
2020/12/12: first drafts, just a skeleton, details still to be worked out
Introduction
Jon Schone (@properprinting) did a “Moving Portal” (MP) mod for his CR-10 in April 2020, and I thought to adapt his approach as “Ashtar M” as Moving Gantry (MG) using CNC terminology.
Instead to move the bed in Y axis to move the entire XZ frame or gantry – the rest of the Prusa i3 style printer remains the same.
Reducing Moving Weight
Ashtar M with Moving XZ frame using modular & parametric V-carriage
This variant only makes sense when the weight of the bed exceeds the weight of the XZ frame + X carriage, in order to reduce the moving weight as of inertia – so only for large(r) build volume this makes sense:
weight(XZ frame + X carriage) < weight(bed)
and as I compose my Ashtar 3D printer series with alu extrusions (beams) I can say:
weight(XZ frame) = beam X * 2 + beam Z * 2 + NEMA17 * 2 weight(bed) = X * Y
and it becomes here clear, the bed weight grows X * Y whereas XZ frame only (X + Z) * 2, but also 2* NEMA17 motors of the Z axis are part of the XZ frame.
XZ frame is static (can hold filament, extruders etc)
T-Slot 2020
V-Slot 2020
V wheel
Draft
At position 0,0,0
Bare view of Y carriage to XZ frame
Adding side pieces “A” & “B”
Side piece “A” Y carriage to XZ frame
Side piece “B” Y carriage to XZ frame
Side piece “B” bottom view
At position 0,0,0
Z motor mount
Y belts & Y motor
Y pulley holder
Y motor mount
For now I decided to use my V modules as Y carriages with width of 100mm vcarriage2(width=100) but actual tests are required how stable the moving XZ frame will be.
As you can see on the draft, I lose some build volume because I stack on top of the Y carriage instead within, but if I put the gantry / XZ frame between the Y carriage I need extra long X beams for the outer frame, and make it impossible to achieve uni-length design (same beam length for all); it’s all about balancing a compromise.
XZ Arch Option
The “XZ Arch” option is removing the lower X beam from the XZ frame, hence, extends Z build space as the print bed also goes lower – for now I moved the Y beams supporting the print bed on the lower framework, details how the print bed will be mounted not yet determined. The side piece “A” is a bit shorter, and side piece “B” is a bit more solid – the way the Y belt is fastened remains the same: Y belt ends come out downward, and are fastened with M3 screws & M3 nuts inserts.
Side pieces “A” & “B” with Arch (lower X-beam removed)
Side piece “A”
At position 0,0,0
Specifications
Build Volume: ~380x400x380mm
Frame: 10x 500mm 2020 alu profiles (XZ arch option)
3x or 5x V-Slot 2020 (X, Y and optional Z axis)
7x or 5x T-Slot 2020
Issues to Resolve
Y motor & Y pulley holder, likely using 6mm smooth or threaded rod as extender, resolved, details defined with 625ZZ bearings
print bed mounting with adjusting nobs to level bed
optional remove lower beam of the XZ frame and make it just a gantry, would allow to lower supporting bed beams (space for springs and nobs etc) – but might introduce weaker XZ gantry geometry
Y Carriage to XZ Frame mount: either combine the L shape of XZ frame, or have a separate piece to attach – that part likely is the most challenging to get right, using two pieces “A” and “B” to connect to XZ frame with Y carriage
resolved in theory, but in actual implementation it will be tricky, as the piece “A” aka ycarriage_xzframe_mount_a() will be printed flat, and quantized by layer height, but the thickness has to be very precise as +/- 0.05mm not to introduce any tilt on the Y carriage (it would damage the V module and/or V wheels and introduce wobble Y-wise), hence 0.1mm layer height required for piece ycarriage_xzframe_mount_a() mounted outside, and ycarriage_xzframe_mount_b() (◤-like piece) mounted inside:
Side pieces “A” & “B” with full XZ Frame
Side pieces “A” & “B” with XZ Arch
Z motor mounts, resolved: how stable it is needs to be tested
cabels & bowden tube routing
XZ frame moves as well – lot of motion involved – likely not put bowden extruder motor on it and avoid to add additional weight again
cable chain to ensure it bends in a controlled manner
Preliminary position of multiple extruders: X back beam, hence, very long Bowden tubes
none of them can be put on the moving XZ frame anymore
tuning to common to build-volume with uni-length beams
likely 400x400mm build plate achievable, but perhaps 380×400 printable, losing 10-15mm on left- and right-hand side.
XZ frame vs XZ arch: to be determined if it’s essential with actual tests
XZ frame (back view)
XZ arch (back view)
build printer
print tests
release parts
release code
Bed
Ashtar K & M bed mounting
The bed is stationary, so it’s relatively simple, a bed carriage it still required so the fine level adjustment is possible with some knobs – using the same setup as for Ashtar K.
Gallery
Parts
Printable Parts
Y carriage:
2x am_v_plate-2020-double-v-244-110-100w-a
2x am_v_plate-2020-double-v-244-110-100w-b
2x am_zmotor_mount
2x am_ycarriage_xzframe_mount_a
2x am_ycarriage_xzframe_mount_b
1x am_ypulley_holder
1x am_ymotor_mount or 2020_Y_motor_mount
4x am_foot_hh
Non-Printable Parts
2x 625ZZ bearings
2x for 1x am_pulley_holder
nx pulleys (dimension not yet determined)
2x (5mm hole) for 1x Y motor, 1x am_ypulley_holder
1x (5mm hole) for 1x X motor
nx idlers (with 3 or 5mm hole)
1x (3mm hole) for 1x X belt
2x (3mm hole) for 2x Y belts
~490-500 mm M5 smooth or threaded rod (Y shaft extension)
See the on-going blog-posts on Ashtar M development, with some more details than the overall page here.
IDEX Option
As Ashtar M shares much of Ashtar K design, the IDEX option comes easily – yet, adding a 2nd motor on the moveable XZ frame/gantry definitely pushes the limits of Ashtar M, significant forces will be applied at high Z positions while moving Y axis.
In order to run two independent printheads (Independent Dual Extrusion) following changes are needed:
