- v2.0 - Extra Chub - March 9th, 2018
Changes and fixes:
- Self-tapping fan screw holes no longer require hulk-like strength to screw into.
- Alignment and tolerances for mounting the stepper and extruder are improved and much tighter.
- Overall strength and rigidity has been improved at the cost of a bit more material and print time.
- Better cable management options and a slot for a zip tie to hold stepper cables.
- Even better thermal performance. The heatsink is now fully ducted, forcing the cold end cooling fan to pull in significant quantities of air from beneath the heatsink, over and through its cooling fins, before finally exhausting the now-hot air out and away from the print head.
- Blower fan nozzle height has been tweaked for better aiming of the air flow at the area immediately beneath the nozzle.
- Y-axis print area loss has been reduced to 10mm.
- Stuff that I've forgotten about still changed, but may not be on this list :).
- v1.0 - December 19th, 2017
IMPORTANT: The Prusa/E3D hotend cartridge thermistor does not fit in the Flexion hot ends. You can use a NTC 3950 100K Thermistor as a drop-in replacement however - your MK2S will never know the difference.
This is a complete extruder and hotend holder design that allows you to mount a Flexion or Flexion HT for i3 style printers for use with your Prusa i3 mk2/s. No special hardware is needed, you can reuse the fasteners you'll obtain from the old extruder body.
I've attempted to make this feel as 'native' to the mk2s as possible, to the point that you can even use the original fan nozzle. It mounts on the stock x-carriage and no parts need to be altered or swapped out, save for the extruder body and extruder cover.
The convective paths for air cooling have been planned carefully, and you should be able to access the full temperature range of the Flexion HT hotend without any plastic parts sagging or deforming even when using PETG.
There is one caveat, and that is that you will lose 12mm of build area along the Y-axis. This is, unfortunately, unavoidable due to stepper motor clearance issues on the extruder. Personally, it's a small price to pay. To compensate for this, see the final step at the end of this page/assembly guide.
Compatible with the regular Flexion as well as the Flexion HT upgrade. Single extruder only. NOT for the E3D version of the Flexion.
If you've been using one of the Noctua hotend fan upgrades, then by all means, continue to use it! :D They should be totally compatible with this new extruder.
Print in any of these materials:
- PETG* (see notes below)
- At least 4 perimeters
- 1.5 - 2mm thickness for top and bottom layers
- A strong infill pattern like triangles, hexagons, cubic, or 3D hexagons
- Have bridging and bridging perimeters turned on
- No supports needed
- At least 20% infill
- Layer heights tested: 0.35mm and 0.2mm. No real advantage to 0.2mm except it looks nicer. Or at least, the ugliness is sharper.
Note: This assumes you have already completed the removal of your old extruder from the x-axis carriage, and have followed Flexion's assembly instructions through step 6. It is also very important to not skip putting a length of PLA filament (it must be PLA) into the extruder before you tighten the set screws of the hobbed gear. The hard PLA filament will correctly align the hobbed gear with the idler wheel, and if it is even slightly off, extruder performance will suffer significantly. I know, because I skipped this step the first time :).
Make sure both set screws are unreasonably tight, then tighten them another quarter turn.
You will need the following fasteners (all of which you should have already from removing and disassembling the old extruder):
1 x M3x40 screw
3 x M3x30 screws
2 x M3x20 screws
4 x M3x18 screws
1 x M3x12 screw
3 x M3 square nuts
4 x M3 hex nuts
Allright, let's start!
Attach the heatsink to the extruder cover using a M3x12 socket screw as shown in the photos. An M3x14 might work as well, but make sure it doesn't block the hole that is at a right angle on the heatsink when screwed all the way in.
No screw yet
A single M3x12 screw is screwed into the bottom of the heatsink.
Rest the Flexion + extruder motor assembly you made earlier on its back, and place the extruder cover and heatsink assembly over the face of the motor, with the heatsink fins pointing outwards away from the motor face. Basically, you're just positioning the heatsink where it would be mounted normally (on the lower two stepper motor mounting holes), but with the extruder body attached to the heatsink.
Sliding the heatsink over the motor.
Line up the holes.
Using an M3x30 screw, attach the heatsink and extruder body to the front of the stepper motor.
The screw in question can be seen near the top.
Slide the assembly into the extruder body, as shown.
Place a square nut in the nut trap located on the bottom, as shown.
Place a second square nut in the second nut trap, which is on the opposite end of the extruder:
Locate the two socket screw holes on the extruder cover that align with the two square nuts you just inserted. Use 2 M3x30 socket screws to attach the extruder body and extruder cover together. Make sure these screws are nice and tight.
Keep all your cabling how it was originally, except for the extruder motor cable, which must be run up and over the top of the x-carraige.
There are 3 nut traps that are used to attach the extruder body to the x-carriage. They can be found by looking along the axis of the 3 mounting holes on the back of the extruder body. There are 2 hex nut traps on the non-motor side, and a single square nut trap on the motor side. Place a nut in each trap.
Now, using 3 screws of your discretion, mount the extruder to the x-carriage exactly like the original extruder was mounted. The 3 holes can handle several different screw lengths, so as long as you chose screws that are long enough to reach their respective nut, there is no problem. I ended up having to use screws a bit long, but that's ok. There are clearance holes that go beyond the nut traps that can accept over-length screws without issue.
First non-motor side trap (with nut added).
Second non-motor side nut trap, located beneath the hotend cooling fan bracket.
Motor side trap.
Now mount the PINDA probe, blower fan, hotend fan, and fan nozzle exactly like you would on the original extruder. Their locations are all exactly the same. Note, only one of the two screw and square nut pairs are needed for the PINDA probe. There are small wedge braces that will keep it rigid and in position with just the screw and nut closest to the print bed holding it in place. The holes for the hotend fan and one of the blower fan holes are self-tapping and don't need a nut. The other blower fan hole uses a nut in an identical fashion to the original extruder.
For more rigidity, you can use an extra long M3x45 screw in place of one of the shorter screws when attaching the hotend fan, so it goes all the way through the heatsink to finally attach directly to the stepper motor. In my experience, this isn't really necessary but it probably won't make things worse either. If you use a noctua fan adapter, then you can use an M3x40 screw.
Sit back, relax, bask in your new high-performance extruder from Diabase Engineering!
Well, we're almost done. Make sure to follow the rest Flexion's assembly instructions for tightening the cam screw and attaching/assembling the hotend. No disassembly of the extruder will be needed to complete the remainder of Flexion's assembly instructions.
When using this extruder mount, please add this gcode to the 'start script' of your prints in your favorite slicer. This is to compensate for the lost y-axis:
G1 Y12 F1500 ; move to Y=12
G92 Y0 ; set this position as new Y0
The flexion extruder has a different hobbed gear radius, so we need to change the steps per mm of our extruder stepper motor to around 94.54. That number worked well for me, but if you want to be really precise, doing an extruder calibration is best.
M92 E94.54 ; Set extruder steps per mm to 94.54
M500 ; Save settings to the EEPROM
The above will semi-permanently change the extruder steps per mm, allowing things like loading and unloading filament to occur at the right speed, and you can keep using all your same extruder multipliers as is. If you do a hard reset of all data on your printer, you might need to send:
M501 ; This will restore the saved EEPROM settings
If you change your mind and want to use the stock extruder, send:
M502 ; This will reset the extruder to the stock Prusa one.
Don't forget to do a full XYZ and first layer recalibration.