Status: playing with ideas; early draft with rotary Z 4 printheads and rotary Y 2 printheads
2021/02/09: matured Rotary Y MSE dual with a servo
2021/01/31: added more drafts and formulated Pros and Cons for Rotary Z MSE, post published, with part cooler
2021/01/29: starting with collecting existing solutions and consider my options, Rotary Y (max 2 printheads) and Rotary Z (max. 4 printheads) design started
Since I dedicated some time for the IDEX upgrade on all the 4 Ashtar Series: K, C, M and D, I realized one of the main advantages of IDEX is to have the non-active printhead aside and not moving over existing prints and certainly not oozing over it.
There is another way to achieve such, by having multiple printheads mounted on the X carriage and mechanically switch them so only one nozzle actually touches the Z plane to print, all other printheads aside and sealing their nozzle with anti-oozing measure like an underlying metal sheet.
As I like to have my own solution in OpenSCAD source, so let’s dive into the design process:
Multiple Switching Extrusions (MSE)
2, 3 perhaps 4 heads switching, only one printhead/nozzle at Z printing head
share one heatsink fan
share one part cooler setup and fan
simple adjustable calibration of X, Y, Z repeatability
ideally interchangable between
E3D V6: proven reliability
Micro Swiss / CR 10 clone: single screw to set Z distance
inactive printheads non-ooze with shield
keep it simple, don’t overengineer, keep construction simple and light
Rotating around the Y axis, suitable for 2 printheads only, as 3 or more printheads use up too much in X space:
Simple design, shared fan is difficult, as I like to go with Micro Swiss as it’s very compact, I likely end up with dedicated heatsink fans as all printheads in use will be heating and the heatsinks require fanned air. The ooze-shields are easy to attach.
132mm / 20°: tall (not good), narrow X space (good)
120mm / 24°: still ok
110mm / 27°: extending X space usage
100mm / 35°: low but extending too much in X
So let’s combine most narrow with a common fan approach, for a compact dual switching printhead/extrusion sacrificing as little X space as possible:
The actual axis of rotation can be moved lower by becoming an arc or swing, which will make the construction more complex, but likely more reliable as the servo cannot be trusted to keep position exact enough – so a spring to keep the swing in either two position, or constant force to push to a left or right limit in dual extrusion setup – for now I use a small SG90 servo to push toward the mechanical stoppers, either left or right hence only usable in dual setup, and using a 1mm wire to connect the swing with the servo.
The Rotary Y approach definitely is only suitable for dual extrusion setup, as anything else, as seen on this comparison, uses up too much X space for my consideration.
Let’s explore another idea . . .
This design is heavier with NEMA17 motor, and with the focus of more than 2 printheads but 3, or 4 printheads, inspired by the Rotating Tilted Nozzle:
I first went for 9 sided regular polygon, and then switch to 360°/9 angle and only make a connector where the heatsink/printhead is mounted to.
I could tilt the other way and regain some of the Y offset, but the Bowden tube and cable of the printheads would clash with the mount – the same problem arise when I would position the full circle with printheads, it looks nice but doesn’t work with Bowden tubes:
So for the moment I stay with 360°/9 angle and explore further on the details with 4 printheads/extrusions.
Ashtar K with Multiple Switching Extrusions (MSE)
Rotary Z with 4 printheads mounted on Ashtar K to see how much space X and Y is sacrificed or otherwise fit with existing design – so far it looks good:
This design is more flexible and extendable, the ooze shields are mounted on the “nose” underneath using metal sheets.
And the Rotary Y with 2 printheads (MSEY2) mounted looks good so far, sacrificing little X space as well:
Issues to Resolve
Rotary Y with Servo
mature draft to something actually promising, done with SG90 servo
strength to hold angle, likely use servo to constantly push toward a mechanical limit, dual mode: left/right limit, tripple mode some kind of spring the servo has to overcome
reposition reliability, some kind of spring mechanism, and servo is only used to “jump” to new position
mount to X carriage, servo clashes with belt mount, resolved
press-fit 625 ZZ bearings based switch axis
sufficiently narrow play/margins for printing? tests needed
Rotary Z with NEMA 17
early draft, untested
mount heatsink fans, done
rotary angle calibration at start, position/tool #0 (0 .. heads_n-1) => tool number (e.g. T2)
either mechanical homing of the rotation to position/tool #0 or
end stop switch to home rotation position
ooze shields. mounting for metal sheets prepared & illustrated
heat creep toward the “nose”?
do ooze shields add to cross-contaminating when changing tools
paying attention to details how to bend metal sheets
mount to X carriage, done
part cooler, will be tricky as, resolved
above mount won’t work due Bowden tubes cross through
mount via “nose” where the non-ooze metal sheets are mounted, done
Marlin firmware tool changing Gcode support with NEMA17 rotating?
printhead (heatsink, heatbreak, heatblock, heat cartridge, nozzle, push fit adapter for bowden)
heating driver on the mainboard
thermistor input on the mainboard
2 printheads: 2x additional NEMA17 (1x rotating motor + 1x additional extruder), 2x 40W = 80W power
3 printheads: 3x additional NEMA17 (1x rotating motor + 2x additional extruders), 3x 40W = 120W power
4 printheads: 4x additional NEMA17 (1x rotating motor + 3x additional extruders), 4x 40W = 160W power
Obviously you need a mainboard with sufficient heating drivers or (1 digital output and MOSFETs per hotend) and thermistor inputs (ADC), the motor drivers can be added to 2 digital outputs (STEP & DIR) and external motor driver. More detailed informotation will be added later.
Very early draft to see how MSE4 looks mounted on Ashtar K, C, D and M: