Chubby: Relaxed Tensioning Lever for Creality Extruders

Creality single-gear extruders, especially the metal ones, come with a very stiff spring and sometimes can, even on their minimum design (screw all the way loose) and true minimum (cap removed) settings, badly deform softer filament, including some PLA+ and PETG.

Deformed filament causes extrusion inconsistencies, particularly when there are many retractions that are also very aggressive, like what's typically required on stock Ender-5's, due to the very long filament path.  It can also cause clogs, if the filament gets so badly deformed that it takes a quasi-semi-circular shape, with the larger dimension surpassing that of the inner diameter of the PTFE tube.  Don't ask me how I know…

Even if you don't have print-ruining issues, excessive pre-tension on these extruders has also been shown to limit your effective maximum flow.[1]

Commonly mentioned solutions to this problem are replacing or cutting the spring.  However, you may find yourself, like me, in a situation where you don't have a suitable replacement spring at hand… which also makes you not want to cut the only one you have.

So, Chubby is a modified extruder lever that increases the maximum elongation of the pre-tensioning spring by, in the current (1.1) version, 2 mm.  This significantly reduces the minimum possible pre-tension setting, while still maintaining nearly the same ability to crank it up to filament-mashing levels, should that need arise.

Chubby is also, err… chubby.  This is to compensate for it being a printed plastic part, and to avoid it breaking like old plastic Creality extruders used to.  To further strengthen the part, a stress concentrator was also removed from the original design. (To be more accurate, the feature was moved away to where it's no longer a relevant stress concrentrator).

The reference dimensions were mostly taken from the open-source Ender-3 mechanical drawings,[2] with additional features like the tube/bushing on the hinge measured from the red metal lever that came on my Ender-5.

Finally, Chubby also features an extended lever, reducing the force required to manually disengage the extruder.

Required hardware

All hardware will likely be borrowed from a stock metal extruder.  But if yours doesn't yet feature the tube/bushing on the hinge, one will need to be sourced, or the design will need to be adjusted to account for its absence.  If you need the measurements, just let me know and I'll include them here.

Tolerance

Extra clearance for FDM 3D printing is built in the model: in most features at most 0.20 mm tolerance is assumed (i.e. your printer doesn't have to be more precise than this), and in some places this has been relaxed further.  Most features in the part are also not that critical, and the FreeCAD model is included should you still need to make small adjustments.

Regardless, once printed, check that:

• the M4 thread for the idler screw is usable (if it's too tight, try to re-cut it; it it's too loose, use some thread lock);
• the filament path isn't constricted and doesn't introduce friction;
• the tube/bushing for hinge, taken from the stock extruder, can still protrude from the back of the lever when that (M3) screw is fully tightened (this significantly reduces friction by not having the entire back of the lever sliding on base plate of the extruder).

Material and print settings

Due to the small amount of heat from the motor, PETG or another strong and somewhat temperature resistant material is recommended.  Creep is also an important consideration.

For reference, after one week my Printalot Black PETG lever has not shown any significant creep.  But different PETGs may have differently, and I've also been using the minimum pre-tension level.  Your mileage my vary.

The model is optimized for 0.20 mm layer height, so that's also recommended.  Regarding infill, consider that the part will be stressed in the transverse direction, so 3D patterns like gyroid are preferable.  Also increase the number of perimeters, as those are the most critical for the strength of the lever.

In summary, my suggested material and print settings are:

• PETG
• 0.20 mm layer height
• 0.4 mm nozzle, 0.45 extrusion width
• 5 perimeters, 6–8 top/bottom layers
• infill: 15% gyroid
• orientation: as in the STL
• supports: none (the spring post should still print well [enough] without them)

Note: these settings slight deviate from how I printed my part, but that's because I made a mistake on my own print.  Still, it's holding, and the settings above should produce a part that's even stronger than it.

Lubrication

The stock metal extruder uses a very thin grease between the flange on body of the lever and the idler bearing.  For now I simply didn't wipe what was left of it on the bearing, and that has been enough; the friction between PETG and steel also isn't that high to begin with.

Still, I asked Creality about this, and they said that common greases are sufficient for this and the other parts of the machine.  So in the future I'll likely try Super Lube 51014 (PTFE oil) or, if that's too thin, Super Lube 21030 (NGIL 2 PTFE grease).  Perhaps the ideal lubricant is somewhere in between those, but these are quality ones I can easily source and use in other applications.

Footnotes

[1] As tested by CNC Kitchen in Everything about Extruder Pre-Tension:

Note that those results are already with a much better than stock hot-end.

[2] The mechanical drawings for the Ender-3 have been published by Creality on GitHub: https://github.com/Creality3DPrinting/Ender-3