An Easy Dual-Hot End Mod for the Creality Ender 3
DavidF6 has an interesting pivoting dual-hot end mechanism that eliminates most of the headaches associated with traditional dual-extruders.
A second extruder can add a lot of very desirable functionality to a 3D printer. Beyond the obvious dual-color prints, you can also get dual-material prints. Mix flexible TPU with rigid ABS. Or print soluble support material that you can easily dissolve after the job is done. But traditional dual-extruder setups, with two extruder/hot end assemblies mount side-by-side and upright, require careful adjustment and are prone to issues. That is why DavidF6 designed this bistable pivoting dual-hot end for Creality Ender 3 printers.
The problem with traditional dual-extruder setups is that they require that the nozzles be exactly the same height, relative to the bed. Put another way: a line between the tips of the nozzles must be perfectly parallel to the bed. And that has to be true even when the extruder carriage moves around on the X axis rail. If there is even a slight difference, one nozzle will print with too much of a Z axis offset, while the other will drag across the freshly printed layers. This pivoting style is more forgiving, because it moves one hot end out of the way while the other is in use. They should still have a very similar offset, but you can compensate in software with standard offset calibration methods for slight differences.
DavidF6 isn’t the first person to think of this and there are other designs out there, including one that Jón Schone designed for the Ender 3 and demonstrated on the Proper Printing YouTube channel a few years ago. Schone used a spring-loaded bistable mechanism that didn’t require a servo motor, but the design didn’t appeal to DavidF6.
A bistable mechanism is one that remains in one of two states until an external force flips it to the other state. A light switch is the most common example in everyday life. There are many ways to achieve that and DavidF6 designed his mechanism to take advantage of magnets.
DavidF6’s design relies on the fact that magnetic strength drops off exponentially. It has magnets to hold the mechanism in either position and uses a servo motor to flip between those positions. It doesn’t take much force to flip positions, but stays securely in place during printing. Now DavidF6 can swap between colors and/or materials as much as he wants during prints.
However, this design won’t work with the stock Creality Ender 3 control board. That doesn’t have support for the extra hot end and extruder, nor for the servo motor. DavidF6 performed this modification alongside an upgrade to Klipper and anyone replicating the project will need to do the same.