Monthly Archives: January 2021

3D Printing: Multiple Switching Extrusions (MSE) – Draft

by Rene K. Mueller · published January 31, 2021 Technology Dual Color, Dual Extrusion, Dual Material, MSE, Multi-Color, Multi-Extrusion, Multi-Material, Multiple Switching Extrusions, No Oozing, Quad Color, Quad Extrusion, Quad Material, Rotary Switching Printheads, Triple Color, Triple Extrusion, Triple Material

Status: early draft with rotary Z 4 printheads and rotary Y 2 printheads

*4 printheads on rotary Z MSE, tool 0 selected*

Updates:

2021/08/01: MSE Z4 printed & mounted
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

Introduction

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.

Existing Solutions on Thingiverse

Panning Dual Hotend for Prusa i3: multiple Bowden tubes, two printheads E3D V6s
Tiny Switch Dual Bowden Extruder: multiple Bowden tubes, two printheads Micro Swiss
Parking dual extruder, Prusa i3 X axis mod, hexagon extruders: two passive X carriages with printheads, single motorized X carriage using magnets to attach passive carriages – quasi IDEX with single X motor – interesting

As I like to have my own solution in OpenSCAD source, so let’s dive into the design process:

Multiple Switching Extrusions (MSE)

Design Goals

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

Drafts

Rotary Y-Wise

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.

increased distance of base to anchor, to support silicon sock on hotend

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.

Addendum: DerM4209 did a design with 6 extruders on full 360° rotary, and as the setup shows, he has plenty X-axis space to dedicate to such.

Let’s explore another idea . . .

Rotary Z-Wise

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:

*4 printheads on 9 sided polygon, 20° tilted*

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:

tilted forward, clashes with mount (**won’t work**)

So for the moment I stay with 360°/9 angle and explore further on the details with 4 printheads/extrusions.

Printable Parts

MSE Y2

Not yet.

MSE Z4

mse_rotz_mount
mse_setup-type=rotaryz,heads_n=4
mse_partcooler_mount
cr10_hotend_fan_mount_simple (4x)
mse_rotz_fannose

Assembly

Each hotend is mounted with 2x M3x20 mounting heatsink, and
2x M3x16 mounting the 30mm fan on top.
4x M3 x 8mm used to mount NEMA 17 on top of mse_rtz_mount, and
4x M3x8 to mount it to the X carriage.
The part cooler mount is attached with M3x10 with a M3 nut and can be adjusted.

Brief tool changing test:

and guiding the PTFE tubes with a guide:

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~~
- alternatively using magnets (e.g. 6mm/0.8mm) on anchor and stoppers: pushing anchor without servo or motor, but pushing carriage to X home left and X home right to switch between two states
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~~
- dual bearings still wobbles in Y-axis (when mounted)
- single bearing doesn’t wobble, more friction when switching

Rotary Z with NEMA 17

early draft, ~~untested~~
- rotation tested: 40° per tool, e.g. G1 A0, G1 A40 in RepRapFirmware (Duet3D boards)
- testing holding torque when printing (nozzle running over overextruded parts)
~~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?
Bowden tube guides, ensuring smooth rotating of Bowden tubes & wires
- rings around NEMA 17, in particular around the edges
- combine tubes & wires above the motor

Considerations

Rotary Y 2

Pros

simple mechanical setup incl. ooze shields
fast switching of extruders

Cons

servo SG90-based: only suitable for dual setup (not extendable to 3 extruders)

Rotary Z 4

Pros

fast switching of extruders
heavier than a servo, but more reliable holding position
simple design, as this design mounts on all of Ashtar Series (K, C, M & D)
2, 3 or 4 printheads/extruders mountable, more flexible than IDEX which only has 2 printheads and requires more modifications

Cons

additional moving weight on X axis (NEMA17)
loss of build volume in X space ~5-10mm left and right
optional loss of build volume in Y space, it can be compensated if printer is used with MSE option only, otherwise some Y space sacrificed as well ~20-30mm
ooze shields may contaminate material to rotating nozzles, needs to be tested
all nozzles are heated even when not currently selected but will be used during the print
- some people still print a purge block to purge material from the nozzle newly selected – fast switching material should be ok, long wait between switches may require purging of material – tests needed

Requirements

Rotary Y

1x SG90 servo
2x 625ZZ bearings
1x M5x25 screw
1x M5 nut
50mm x 1mm wire, bend as hinge

Rotary Z

1x rotating motor (NEMA17 20/25/39 mm) with motor driver
per additional printhead (given there is a single printhead already installed)
- an extruder (incl. NEMA17)
- motor driver on the mainboard
- printhead (heatsink, heatbreak, heatblock, heat cartridge, nozzle, push fit adapter for bowden)
- heating driver on the mainboard
- thermistor input on the mainboard

So for

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.

Gallery

Very early draft to see how MSE4 looks mounted on Ashtar K, C, D and M:

Ashtar K has sufficient space for extruders
Ashtar C may have more extruders, not sure where beyond 4 extruders
Ashtar D reaches its limits with 4 mounted extruders, unless the controller/display is moved away
Ashtar M might not be the best candicate to have a heavier X carriage as it will affect print quality at higher Z positions

I keep updating this blog-post as I progress.

Comparison Dual/Multi Color/Material Extrusions

blue = relevant positive
red = relevant negative

Independent Dual Extrusions (IDEX)

complex setup
moderate cost
non-mixing
dual nozzles
dual heatblocks
dual heatsinks
normal retraction
no purge block ¹⁾
no oozing over print
no inactive nozzle traveling
reliable ²⁾

★★★★★

Dual Hotends 2-in-2

simple setup
low cost
non-mixing
dual nozzles
dual heatblocks
dual heatsinks
normal retraction
no purge block
inactive nozzle oozing over prints
inactive nozzle travels over print
moderate reliability

★★★★★

Chimera 2-in-2

simple setup
clone: low cost
original: high cost
non-mixing
dual nozzles
dual heatblocks
single heatsink
normal retraction
no purge block
oozing of inactive material
inactive nozzle travels over print
moderate reliability

★★★★★

Cyclops 2-in-1

simple setup
clone: low cost
original: high cost
mixing
single nozzle
single heatblock
single heatsink
normal retraction
purge block required
no oozing of inactive material
clone: unreliable

★★★★★ (clone)

Cyclops NF 2-in-1

simple setup
low cost
non-mixing
single nozzle
single heatblock
single heatsink
complex retraction
no oozing of inactive material
moderate reliability

★★★★★

Diamond Hotend 3-in-1

complex setup
clone: low cost
original: high cost
mixing
single nozzle
single heatblock
3 heatsinks
tricky retraction
purge block required
no oozing of inactive material
moderate reliability

★★★★★

Multiple Switching Extrusions (MSE) 2-in-2, 3-in-3, 4-in-4

moderate complex setup
requires additional servo or motor
extendable 2, 3, or 4 colors/materials
low cost
non-mixing
multiple nozzles / heatblocks / heatsinks
normal retraction
no purge block ¹⁾
no oozing of inactive material
no inactive nozzle touching print
reliable ²⁾

(rating comes later)

Y Splitter x-in-1

simple setup
extendable 2, 3, or 4 or more colors / materials
low cost
non-mixing
single nozzle
single heatblock
single heatsink
complex retraction
purge block required
no oozing of inactive material
moderate reliability

★★★★★

Tool Changer

complex setup
extendable to n-colors or materials
moderate cost
non-mixing
multiple nozzles / heatblocks / heatsinks
normal retraction
no oozing of inactive material
no inactive nozzle touching print
moderate reliability

(rating comes later)

Footnotes

in theory no purge block, but if ooze shields are shared among switching extrusions (more than 2 extrusions) there may be cross-contamination between colors/materials
the printheads individually are proven to be reliable

Hints:

single heatblock = same print temperature
dual heatblock = different print temperatures possible
dual nozzle = different nozzle sizes possible

That’s it.

3D Printing: Rotating Tilted Nozzle 4th Axis Option – Draft

by Rene K. Mueller · published January 27, 2021 Technology 4 Axis, Conic Slicing, Rotating Tilted Nozzle, RotBot, Z rotation, ZHAW

Status: prototype doing test prints

Updates:

2021/05/31: first prototype photos with dry run
2021/03/13: fallback printing horizontal slices animation added
2021/03/01: added brief animation of simulated print of conic sliced overhang model
2021/02/23: added brief animation (Zrot=-180° .. 180°)
2021/01/31: maturing printhead with heatsink fan and part cooler
2021/01/28: Outside/Inside Cone printing explained with example, Considerations (Pros/Cons) added
2021/01/27: more detailed illustrations and slicing renderings, published as a draft
2021/01/22: adding conic slicing examples
2021/01/21: first version with rotating bowden printhead

I will update this blog-post as I progress or find other people with alike ideas and summarize the findings.

Introduction

RotBot by ZHAW School of Engineering Zurich

As featured on Hackaday January 16, 2021 and other sites, a “Novel 4-Axis 3D Printing Process to Print Overhangs Without Support Material” by ZHAW School of Engineering (Zurich, Switzerland), from the abstract of the paper:

[..] a novel 4-axis FDM printing process with a newly designed printhead, for the printing of overhangs without support structures. With conventional FDM printing, overhangs of more than 45deg–60deg must be supported.
For this novel printing process, the printhead is rotated 45° around a horizontal axis and equipped with a vertical, rotational axis. The printhead no longer follows layers parallel to the build platform, but moves on the surface of a 45deg cone. The printing cone increases in diameter from layer to layer. With this cone-shaped layers, the printable angles increases by 45°, which leads to printable overhangs of up to approximately 100°.
New slicing strategies for this printing process have been developed to slice the parts for the novel printing process. The feasibility of the concept has been prototypically demonstrated. The novel design achieves the advantages of higher speed and quality with lower cost at the same time.

A brief video sequence of printing (YouTube) shows the machine movement. Unfortunately, as of 2021/01 not much more details have been published by ZHAW except a paywalled paper [sigh] which contains useful overview of their research. I contacted ZHAW and Michael Wuethrich mentioned that they are in negotiations with different companies to develop a product (2021/01) and eventually release the details of their slicing approach with pre- and post-processing while using an ordinary slicer.

Update 2021/02/27: I started with a 4-axis conic slicer.

Rotating Tilted Nozzle (RTN) Option

I thought to try my own implementation of this Rotating Titled Nozzle 4 Axis option. The main idea to keep the entire hotend in Bowden style and rotate that around only once (non-continuous) with all wires, that would simplify things greatly:

The challenge is the +/-180° position when the nozzle opening looks forward, where the printhead bowden tube (and all cables) comes most close to the X beam. As a consequence only -180° to +180° rotation is allowed and not multiple revolutions.

It would also mean, once the printhead reaches -180°, and it has to rotate to +180° and decrease from there again to fulfill 360° rotation – whether this is suitable has to be seen, this likely creates a seam there.

The main advantage of this simplified 4 axis approach is to use existing pieces plus just an additional NEMA 17 motor.

Update 2021/01/26: Wuethrich from ZHAW mentioned that they started first also with a full printhead rotating but then switched to the more complex continuous rotating printhead to avoid a seam, have direct drive extruder, faster prints as simpler decision making to change rotation direction and no start/stop of rotation and de/acceleration when reaching -180/+180° position.

Single Revolution with Rotation Shadow

As I pondered on the limits of single rotation approach, there is a range where the bowden tube (and all wires with it) is touching and bending on the X carriage or printhead holder – let’s call it the rotation shadow – ideally it would be zero or slightly sub-zero to have a bit overlap to conceal a possible seam with “ironing” the section (move nozzle over section without extruding).

E3D Volcano

My first attempt is modeling with E3D Volcano hotend like the RotBot by ZHAW:

Micro Swiss / CR 10 Hotend

And as alternative the smaller Micro Swiss / CR 10 printhead which gives significant more space for the bowden tube (and all wires with it) to bend or flex near -180/+180°:

Comparison Volcano vs Micro Swiss

At this point I continue with the Micro Swiss (MS) option, as the smaller heatsink gives me more space to make full 360° turn with -180° to +180° and have ~0° rotation shadow, perhaps even sub-zero as of overlapping.

This particular Swiss Micro clone aka CR10 hotend comes without screws stabilzing the heatblock, and just a small worm-screw fastening the heatbreak on the heatsink, yet make it easy to adjust the overall length, which in this case is desired.

Prototype

Eventually I took the time to print and assemble my Micro Swiss-based Rotating Tilted Nozzle (RTN):

First test run revealed:

rotation 170°..180° and -170°..-180° were not reliable with NEMA 17 37mm as skipping steps due the stiffness of PTFE tube with filament – resolvement: increase arm length (away from X carriage down/forward)
- partially resolved by limiting A to -170°..170°: M208 A-170 S1 and M208 A170 S0 in config.g of Duet 3 Mini 5+ setup
~~micro swiss / CR 10 hotend heatblock socket touches the bed (same height as nozzle)~~, fixed due slight tilt from X carriage due weight, newer design allows angle readjustment
~~single rotation requires refinement by the Slicer4RTN~~, addressed partially with Slicer4RTN 0.6.0, might require more fine-tuning.

I’m focusing on the hardware-side on the Penta Axis (PAX) 5-Axis printhead and transfer some of the experiences back into the RTN design.

Slicing for Rotating Tilted Nozzle: Conic Slicing

I had to visualize the novel conic slicing approach as mentioned in the article and in the video:

*Rotating Tilted Nozzle: Outside Cone – tilted print plane with Z axis rotating leads to conic print plane*

f(Z_rot, C_height, R) ⟹ X, Y, Z

X = sin(Z_rot) * R
Y = -cos(Z_rot) * R
Z = C_height / sqrt(2)

Z _rot = atan2( -Y, X )
R = sqrt( X*X + Y*Y )
C_height = Z * sqrt(2)

A single conic slice is covered by Z_rot, C_height and R, whereas slices are separated by increasing Z offset to C_height, forming conic slices on top of each other:

Let’s inspect the motion of a single layer: it’s curved – obviously – in X, Y and Z – this means, the Z axis has way more motion than in cartesian XZ Prusa-Mendel setup where the Z axis only changes once a layer is finished, here with cone-slicing every trace or track all traditional 3 axis are in motion, plus the 4th – the tangent on that conic trace.

Multiple solids sliced planar and in conic manner

See more details on Conic Slicing for Rotating Tilted Nozzle (RTN).

Different Print Modes

The 45° tilted printhead allows three print modes:

non-rotation nozzle with planar Z layers (with ordinary slicer), acts like belt-printer in one direction: overhangs in one direction without support
rotation nozzle with planar Z layers (requires dedicated slicer), might support near 90° overhangs of a certain length in all X/Y plane directions as well – but needs to be tested
rotation nozzle with conic Z layers (requires dedicated slicer or pre- and post-processing while using ordinary slicers)

And by choosing the position of the “axis” of the conic slicing within the model and the cone direction matters then as well:

The last piece with inside and outside looking overhangs requires a switch of nozzle direction, e.g by default the sliced cones are ordered ▲ (outside-in or outside-cones) where outward overhangs work, but for inward overhangs the opposite direction of the nozzle looking outside is required ▼(inside-out or inside-cones), like this piece:

*Vertical splitted: bottom half with overhang toward cone axis Inside Cone print,*
*upper half with overhang away from cone axis Outside Cone printing,* **all without support**

So the slicing software needs to recognize this, and the sliced cones switched either ▼ or ▲ according Z level.

These aspects opens a whole new range of considerations how to orient a piece and where to position the newly introduced slicing axis, and which kind of cones need to laid at which level.

Issues to Resolve

Heatsink fan mount: needs to be mounted for both variants, Micro Swiss and E3D Volcano ideally
Part cooler:
- have the part cooler rotate on Z axis as well? yes for now
- ~~using a flexible pipe to blow air near the nozzle instead~~

Z rotation calibration:
- alike with X or Y stop, but a trigger rotating from one direction only and then set a angle offset
Z rotation motor mount adaptable for different kind of printheads
- keep it modular
- ensure the nozzle end is centered (allow simple center calibration)
Properly document design and features of Rotating Tilted Nozzle as there isn’t much detail information available
3D printer firmware support
- Marlin: support for 4th axis?
3D slicing software support
- adapt ZHAW’s approach with pre- and post-processing but use existing slicers; Update 2021/02/26: separate blog-post going into the details of Conic Slicing
- dedicate slicer for conic slicing, e.g. adapt Mandoline Py

Considerations

Pros

conic layers: printing 90° overhangs without support, given some conditions are met:
- overhangs must be horizontally or vertically rotational symmetric and aligned with the cone axis to switch from outside to inside cone printing or vice-versa (to do: more use cases explored and documented)
conic layers: stronger pieces as layers cross X, Y and Z in non-planar manner, mechanical forces distribute further than just planar layers
planar layers / rotating nozzle: perhaps close to 90° overhangs (speculative) requires new overhang algorithms in slicer

Cons

additional mechanical complexity
- fine-tuning nozzle center calibration
additional slicing software complexity
- new slicer software supporting different printing modes (conic layers, planar layers w/ rotating nozzle)
- conic layers: more things to consider (preferably recognized by the slicing software):
  - overhangs must be horizontally or vertically rotational symmetric and align with cone axis to take advantage of it (complex compartmentalizing of different cone-direction per overhang and newly introduced seams between those)

Ashtar K with Rotating Tilted Nozzle (RTN)

The additional Y offset is about 20mm, and losing apprx. 50 mm in Z build volume in its current form:

Ashtar K RTN printing conic sliced overhang model (animated)

Fallback Print Horizontal Slices

Some parts may not require conic slices, e.g. introducing new unprintable overhangs which in horizontal slices would not exist, so a simple way to print traditional sliced models is by adding a proper rotation angle (e.g. G-code A..) so the nozzle extrudes nicely, something like:

Horizontally sliced 20mm cube printing with enhanced G-code with `rtnenhancer`

I wrote a small script called rtnenhancer which converts existing G-code to enhanced G-code.

References

Novel 4-Axis 3D Printing Process to Print Overhangs Without Support Material (english) by ZHAW
Multi-Axis 3D Printing Technique Improves FDM Strength Over 2X (see also paper)

3D Printer: IDEX for Ashtar K, M, D and C (2021/01)

by Rene K. Mueller · published January 15, 2021 Technology Ashtar 3D Printer Series, Dual Extrusion, IDEX, OpenSCAD

Updates:

2021/01/31: added comparison regarding Multiple Switching Extrusions (MSE)
2021/01/18: added IDEX Features with Pros/Cons, Ashtar Series Genealogy, Comparison Dual Material approaches, and brief Hardware Requirements
2021/01/15: first version with overview side-by-side

Mid of January 2021 (01/12 – 01/14) I added IDEX (Independent Dual Extrusion) option to 4 designs, all still in early draft stage – here as a summary side-by-side:

Ashtar K IDEX has been fairly easy, as I was using an improved “old” design of the X motor mount for the 2nd motor and 2nd belt, and since Ashtar M IDEX is using the same XZ frame, it was a matter of a few minutes to port that option as well.

Ashtar D IDEX with Classic XY belt routing was more tricky as there was little space left to add another motor, so I realized I need to utilize what’s there and take advantage of it – result is a very space saving solution, but it needs to be verified in real life first.

Ashtar C IDEX with Core XY with an additional X motor was easy, I just reused a slightly altered X motor/pulley mount of Ashtar D, so that was done fairly quickly as well, yet the challenge will be the firmware support, as currently (2021/01) only Duet RepRap firmware supports the CoreXYU as my design falls under.

Features of IDEX

Pros:

double printing: duplicate or mirror mode
- double printing volume at same duration
two materials with different melting points
two colors (non-mixing) with
- more reliable than dual nozzle setups, as inactive nozzle does not run over existing printed piece often
possibly different nozzle sizes
- dedicated nozzle for infill vs outline

Cons:

slightly reduced build-volume in X-axis
added complexity

Comparison Dual/Multi Color/Material Extrusions

blue = relevant positive
red = relevant negative

Independent Dual Extrusions (IDEX)

complex setup
moderate cost
non-mixing
dual nozzles
dual heatblocks
dual heatsinks
normal retraction
no purge block ¹⁾
no oozing over print
no inactive nozzle traveling
reliable ²⁾

★★★★★

Dual Hotends 2-in-2

simple setup
low cost
non-mixing
dual nozzles
dual heatblocks
dual heatsinks
normal retraction
no purge block
inactive nozzle oozing over prints
inactive nozzle travels over print
moderate reliability

★★★★★

Chimera 2-in-2

simple setup
clone: low cost
original: high cost
non-mixing
dual nozzles
dual heatblocks
single heatsink
normal retraction
no purge block
oozing of inactive material
inactive nozzle travels over print
moderate reliability

★★★★★

Cyclops 2-in-1

simple setup
clone: low cost
original: high cost
mixing
single nozzle
single heatblock
single heatsink
normal retraction
purge block required
no oozing of inactive material
clone: unreliable

★★★★★ (clone)

Cyclops NF 2-in-1

simple setup
low cost
non-mixing
single nozzle
single heatblock
single heatsink
complex retraction
no oozing of inactive material
moderate reliability

★★★★★

Diamond Hotend 3-in-1

complex setup
clone: low cost
original: high cost
mixing
single nozzle
single heatblock
3 heatsinks
tricky retraction
purge block required
no oozing of inactive material
moderate reliability

★★★★★

Multiple Switching Extrusions (MSE) 2-in-2, 3-in-3, 4-in-4

moderate complex setup
requires additional servo or motor
extendable 2, 3, or 4 colors/materials
low cost
non-mixing
multiple nozzles / heatblocks / heatsinks
normal retraction
no purge block ¹⁾
no oozing of inactive material
no inactive nozzle touching print
reliable ²⁾

(rating comes later)

Y Splitter x-in-1

simple setup
extendable 2, 3, or 4 or more colors / materials
low cost
non-mixing
single nozzle
single heatblock
single heatsink
complex retraction
purge block required
no oozing of inactive material
moderate reliability

★★★★★

Tool Changer

complex setup
extendable to n-colors or materials
moderate cost
non-mixing
multiple nozzles / heatblocks / heatsinks
normal retraction
no oozing of inactive material
no inactive nozzle touching print
moderate reliability

(rating comes later)

Footnotes

in theory no purge block, but if ooze shields are shared among switching extrusions (more than 2 extrusions) there may be cross-contamination between colors/materials
the printheads individually are proven to be reliable

Hints:

single heatblock = same print temperature
dual heatblock = different print temperatures possible
dual nozzle = different nozzle sizes possible

Hardware Requirements

1x NEMA 17 42-45Nm with wire, extra stepper motor driver on motherboard
100-110cm long 6mm wide GT2 belt
1x pulley and 1x idler
1x hotend (nozzle, heatblock, heat cartridge, heatbreak, heatsink), extra heating connector on motherboard

That’s it.

3D Printing: Ashtar C IDEX (Independent Dual Extrusion)

by Rene K. Mueller · published January 14, 2021 Technology Ashtar C, Ashtar C 3D Printer, CoreXY, CoreXYU, IDEX, OpenSCAD

Status: just a draft

Updates:

2021/01/14: quick start with a rough draft

Introduction

Well, after the IDEX option designs – still as drafts – worked for Ashtar K (Prusa i3), Ashtar M (Moving Gantry) and Ashtar D (Classic XY), I thought, why not also target Ashtar C (Core XY).

Ashtar D IDEX is definitely a narrow design, so I thought to reuse two parts of it for Ashtar C as well, and hopefully the A and B belts route around – and well, it seems mechanically to work out.

On the firmware part it seems this CoreXY plus additional X motor is called CoreXYU and supported by Duet RepRap firmware – but details need to be researched in more depth. On the first glance the “traditional” CoreXYU setup routes the U belt off the X beam and not place a motor on it as I do, but routes at the end of the frames so the motor is stationary – definitely something also to look at.

Draft

The A/B belts route around the new X motor mount (borrowed from Ashtar D design)

Gallery

Issues to Resolve

Firmware supporting CoreXY IDEX:
- E1: X & Y provided through CoreXY by motors A & B
- E2: X provided by X motor, Y provided by CoreXY where X=0 remains (both motors A & B have to operate to provide X=0 while Y is moved)
- Duet RepRap firmware provides CoreXYU support, and it seems it would cover my use case here
- Marlin firmware as of 2.x does not support CoreXYU yet
Moving the X motor – or U motor as in CoreXYU context – off the X beam and route a much longer belt and place the motor stationary like the motors A & B of CoreXY
Ooze prevention (same issue as with Ashtar D IDEX)

As I progress I will update this blog-post, and summarize also the developments in the Ashtar C project page.

References

CoreXYU: Dual Head for CoreXY, another more complex approach where 3rd motor is also stationary

That’s it.

3D Printing: Ashtar D IDEX (Independent Dual Extrusion)

by Rene K. Mueller · published January 14, 2021 Technology Ashtar D, Ashtar D 3D Printer, IDEX, OpenSCAD

Status: just a draft

Updates:

2021/01/14: starting the draft, very experimental

Introduction

After just few hours working on IDEX option for Ashtar K and Ashtar M, I thought to try myself on doing IDEX on the very delicate Y carriage on Ashtar D – and after an hour roughly I realized, perhaps it is doable.

The main idea is to reuse the NEMA17 shaft as axis for the idler of the 2nd belt, ~~and use 3mm diameter shaft with 5-10mm length as extension, and stabilize the extension in the idler itself~~ likely the shaft seems long enough by itself – the most space saving option:

*Reusing NEMA 17 shaft as axis for idler*

If possible, rotate entire X motor mount / carriage and mount it on the other X side.

Draft

I had to color the belts and V modules, as I otherwise get confused while fine-tuning the design within such narrow margins:

X1/E1 in green
X2/E2 in red

I just love symmetry!
I just love symmetry!

Gallery

Issues to Resolve

X motor-mount isn’t fully Y symmetric yet, it’s off by a few mm; needs some further fine-tuning until X2 motor-mount mounting holes align with V module, resolved
V module belt mount for X2 needs be adapted, as I can’t mirror it as that “back” mirrored is the “front” side where the printhead is mounted and occupied already, a new piece is required which mounts within the V module
- dedicated piece ad_xcarriage_beltmount(idex=true) required
ooze prevention in rest position: some sort of metal sheet close by where the printhead’s nozzle can rest
mature Ashtar D design sufficiently beyond draft stage

As I progress I will update this blog-post, and update the Ashtar D project page as well.

That’s it.

3D Printer: Ashtar K IDEX (Independent Dual Extrusion)

by Rene K. Mueller · published January 12, 2021 Technology Ashtar K, Ashtar K 3D Printer, IDEX, OpenSCAD

Status: verified design

Updates:

2021/07/30: design printed and mounted
2021/01/19: improved 2nd X motor mount
2021/01/15: removable/replaceable ooze prevention
2021/01/14: Ashtar M (Moving Gantry – Draft) also with IDEX option now
2021/01/13: ooze prevention at rest position added, mechanical conflict resolved
2021/01/12: starting with a first draft, one mechanical conflict to be resolved

Introduction

I have been pondering on a dual independent X axis upgrade or option for a while, but the other designs of the Ashtar Series I wanted to do first (Ashtar D and Ashtar M) those matured by now (2021/01), so I decided to get back to IDEX upgrade for Ashtar K:

For now I like to keep single 2020 V slot alu extrusion for the X beam where the X carriage rides, and route the 2nd belt above for the 2nd X carriage – and this was a quick solution as earlier version of Ashtar K had the belt routed above the alu profile so I just reused the old pieces again.

“Above routed belt” option with its pieces are weaker and ~~possibly need enforcement~~ improved the strength, so it’s a fast start – just took me 2 hours – but needs definitely some fine-tuning. ~~Alternatively the 2nd belt could be routed at the back of the X carriages, but fastening the 2nd X motor would be challenging.~~

For now I use the same code base of Ashtar K and introduce IDEX = true flag, and enhance a few existing pieces in parts.scad and optionally add those new pieces when rendering printer-ak.scad.

As I progress with this option or upgrade I update this blog-post.

Draft

Issues to Resolve

X carriage #1 belt mount conflicts mechanical with belt 2: redesign xcarriage_beltmount_2020 piece, make it shorted in Z or fasten it inside V module: resolved, shifted 2nd belt a bit Y off, and shorten xcarriage_beltmount_2020(idex=true) by 2mm.

*2nd belt slight Y offset so X belt mount #1 doesn’t touch belt #2*

“Above routed belt” pieces are weaker: enforcement required, resolved: piece strengthened (2021/01/19):
- xcarriage_short_hmount_motor_2020 which is the base piece which routes the belt within the 2020, with idex=true option provides idler holder on top
- X motor #2 is mounted on a x-mirrored version of xcarriage_hmount_motor(20,"left",idex=true) but definitely needs reinforcement, added ooze prevention in case of idex set

Nozzle drip prevention:
- using a piece of sheet metal which the nozzle moves over when in rest position left or right, first attempt done (see below)
- and/or use purge box with brush to clean nozzle after and before use
- ~~make extending “nose” detachable/replaceable as it’s expected to break or overheat otherwise entire X motors mount needs replacement~~, resolved
  - xcarriage_nose-idex-left and xcarriage_nose-idex-right with 10mm wide sheet metal insert
- how dealing with long resting hot nozzle?
  - drop temperature by 5-10°C in rest position, and heat up when in use again
  - heat creep possible weakening extending printed nose – heat insulation required attaching sheet metal

Inside and Above 2020 belt routed X motor mount, w/ removable nose with ooze prevention

Gallery

Ashtar M IDEX

And since Ashtar M (Prusa i3 Moving Gantry – Draft) shares much of the Ashtar K design it took me a few mins to add the IDEX upgrade option as well:

References

BCN3D Technology IDEX, some background info on IDEX
EnderIDEX Dual X-Axis Kit, simple upgrade for Ender 3, also with above routed belt
Rat Rig V-Cast IDEX, alu extrusion-based prefab kit

3D Modeling: Random Snapshots 2020

by Rene K. Mueller · published January 12, 2021 Art, Technology OpenSCAD, Photos, Screenshots

*Ashtar M with 3 extruders, LCD controller*

3D Printer: Ashtar K History 2018-2020

by Rene K. Mueller · published January 5, 2021 Technology Ashtar K, Ashtar K 3D Printer, History, OpenSCAD

A brief history of “Ashtar K“, my first designed 3D printer I actually built – documented also for my own sake:

AluX: Prusa i3 Clone

It started with AluX (abbreviation of ALU-extrusion eXtendable) early June 2018, which used CTC i3 Pro B / Prusa i3 Clone pieces as the X carriage, X motor mount and X idler all in STL format. I coded the frame parametric using 2040 alu extrusions/profiles and using smooth rods as rails:

I realized then quickly I need to design and code my own pieces, every single piece I need to control and make it parametric if it makes sense, and not rely on existing STL files, as editing meshes of the STL seemed a waste of time but rather design the piece in OpenSCAD right away and derive new variants if necessary from the geometry itself.

Ashtar X & W Series: Riding on Smooth Rods

Mid June 2018, AluX became Ashtar X (abbreviated as AX), and Ashtar W were using 2040 alu extrusions but differently oriented at the base, still using smooth rods as rails:

At this point I got sufficient experience of the parametric approach and it was obvious to use the frame as rails.

Ashtar T Series: Riding Alu Profiles

Beginning of July 2018, with the Ashtar T series I began to use the frame as rails itself, utilizing 2040 alu extrusions, it also started with the parametric V module (due its shape) composed by 2x V-plates, using 3 wheels which ride on the alu extrusion:

With the parametric V modules the X, Y and Z frame beams became rails as well, simplifying the overall construction compared to earlier designs:

The dual Z motors still residing in the front for sake of accessibility, but then I realized I want them in the back and keep the front dedicated to the printhead.

Ashtar K Series: Riding Alu Profiles, Uni-Length Beams

Mid of July 2018 I started the Ashtar K series, I decided to use 2020 alu profiles and focused on the single length of alu profiles, uni-length so I could reuse the beams for other future designs and since all the designs were parametric, it was easy to attain to find an optimum of single length beams and a common build-plate or build-volume:

The 9 beams design turned out too weak when I actually built the printer, so I added two beams back on left and right, and lift up the 9 beam design.

Eventually I decided to use 500mm alu 2020 profiles to achieve ~380x300x360 build volume; Ashtar K #1 used 400×300 build-plate, and Ashtar K #2 300×300 build-plate. Ashtar K #1 was functional in August 2018, and since then became my working horses together with Ashtar K #2, reliably printing.

See more at Ashtar K project page of the current state.

Next Steps

After the Ashtar K I did the Ashtar C Core XY cubic frame also with 2020 alu profiles. Late 2020 I started to design Ashtar M, a derivative of Ashtar K but with a moving gantry and static bed, and Ashtar D with Classic XY alike Ashtar C; and also a draft of a parametric enclosure as well to be adaptable to all of my 3D printer designs.

That’s it.

3D Printing: Simple Compact Extruder with 625ZZ Bearing

by Rene K. Mueller · published January 1, 2021 Technology Bowden Extruder, Compact Extruder, Direct Drive Extruder, Extruder, OpenSCAD, Simple Compact Extruder

Updates:

2021/01/01: sufficiently tested, finally published
2018/12/20: starting with write-up

I used some aluminium MK8-based extruders but realized I required my own parametric extruder using 625ZZ bearing and I looked around and found Compact Bowden Extruder by Dominik Scholz which uses 608ZZ and adapted the overall design but coded it from scratch again in OpenSCAD with 625ZZ bearing for the Ashtar Series:

It’s “right handed” by default, but filament can go both directions. The handle is pushed from inside out with a spring, not so elegant, yet it saves space and filament does not have to go through the handle this way, which I prefer.

Bill of Materials (BOM)

M5x14 or M5x16: mounting bearing
2x M3x8: mounting base to stepper motor
2x M3x25: mounting handle and spring
M3 nut: insert into slot
M3 washer (or print it): hold spring
20-25mm long soft spring (ID 3.2-8mm) or alike
hubbed gear OD 11mm (MK8)
625ZZ bearing

Recommended further:

PTFE OD 4mm, ID 2mm
PC4-M6 straight fitting

Building

Software

compact_extruder() takes following parameters, in case you like to recreate the pieces:

type:
- "base": the base attached to the NEMA 17 stepper motor
- "handle": the push handle with the spring
- "indicator": small indicator to put on the axis of the stepper motor
mount:
- "none": (default) just attaches to NEMA 17 stepper motor
- "mount": simple mount (center)
- "2020": extends flat (lower left version)
btd: Bowden tube diameter (default: 0), if 4mm is used, then Bowden PTFE OD 4mm/ID 2mm tube can be inserted on both sides as guides for flexible filament close to the hobbed gear as shown below
m5 can be redefined, e.g. 14 then it sinks in

Hardware

I use PC4-M6 push fit connector with PTFE tube 4mm OD / 2mm ID as guides, and began to use it right away on 3x printers for first tests:

Assembled Simple Compact Extruder (M5x16)

Download

https://www.thingiverse.com/thing:3265864

includes STLs and OpenSCAD source code of the module

Applications

Compact Extruder on Ashtar K #1 in Bowden setup

Direct Drive Extruder

A small adapter allows to mount the Compact Extruder close to the printhead to use it as Direct Drive Extruder:

Compact Extruder in Direct Drive E3D V6 Setup

I did not test the Direct Drive approach as I prefer the Bowden setup on my printers, but have it ready when needed, e.g. for flexible filament.

References

Compact Bowden Extruder 608ZZ Bearing by Dominik Scholz, adapted his overall design but coded it from scratch
Compact Bowden Extruder 625ZZ Bearing by Jake D, uses 625ZZ but had no OpenSCAD source

Introduction

Existing Solutions on Thingiverse

Multiple Switching Extrusions (MSE)

Drafts

Rotary Y-Wise

Rotary Z-Wise

Printable Parts

MSE Y2

MSE Z4

Assembly

Ashtar K with Multiple Switching Extrusions (MSE)

Issues to Resolve

Rotary Y with Servo

Rotary Z with NEMA 17

Considerations

Rotary Y 2

Rotary Z 4

Requirements

Rotary Y

Rotary Z

Gallery

Comparison Dual/Multi Color/Material Extrusions

Introduction

RotBot by ZHAW School of Engineering Zurich

Rotating Tilted Nozzle (RTN) Option

Single Revolution with Rotation Shadow

E3D Volcano

Micro Swiss / CR 10 Hotend

Comparison Volcano vs Micro Swiss

Prototype

Slicing for Rotating Tilted Nozzle: Conic Slicing

Different Print Modes

Issues to Resolve

Considerations

Ashtar K with Rotating Tilted Nozzle (RTN)

Fallback Print Horizontal Slices

References

See Also

Features of IDEX

Comparison Dual/Multi Color/Material Extrusions

Hardware Requirements

Introduction

Draft

Gallery

Issues to Resolve

References

Introduction

Draft

Gallery

Issues to Resolve

Introduction

Draft

Issues to Resolve

Gallery

Ashtar M IDEX

References

AluX: Prusa i3 Clone

Ashtar X & W Series: Riding on Smooth Rods

Ashtar T Series: Riding Alu Profiles

Ashtar K Series: Riding Alu Profiles, Uni-Length Beams

Next Steps

Bill of Materials (BOM)

Building

Software

Hardware

Download

Applications

Direct Drive Extruder

References

See Also