3DPrinting

Multi extruder printing is very hard and no one has done it well for hobbyist hardware so far.

The issue is technical, but not too hard to understand. One of the main reason hobby machines are cheap is because these are Open Loop linear actuation systems. This is opposed to Closed Loop systems found in more industrial machines. Open Loop calibrates close to a known location using some form of end stop. Computationally, this location is set as "0, 0" Home and all motions are relative to this Home. There is no additional feedback in the motion system. In a closed loop system there is an additional set of sensors that confirms if each linear motion system produced the desired motion.

The difficulty with dual extruders is that the Home location isn't actually repeatably accurate. It doesn't matter if Home is slightly different every time because every movement is relative to this location. You never see the slightly different location because they can not be compared.

If you haven't encountered this issue before, you are likely thinking it is easy to solve, but let me help crush some assumptions. Virtual endstops have a large range of triggering and are nowhere near absolute position or repeatable. Physical switches are slightly better but not even remotely close to absolute position reliable. Their leverage and metal spring contacts never actuate exactly the same and every pairing of contacts will produce slightly different electrical properties. In addition, every stepper motor is slightly different and microstep positions are not entirely equal in the application of force. These uncertainties all add up to a system where it is ~~nearly~~ impossible to know exactly where the actuator is located. This does not matter when you only have the one print head. The second you need to align two heads, this is a gigantic problem. The only real effective solution is to use a closed loop linear motion system and add a shared gate that both actuators on the same axis can home to. This involves a sensor like an optical encoder on each print head that passes a stationary interrupter that triggers the encoder. This will get at least one axis aligned. You still need to account for the nozzle's offset relative to each other and this is another far more complicated than it first seems X-Y-Z measurement issue.

These are hard problems to solve and no one has solved them well. The evidence is easy to measure. Many of us have wanted IDEX (independent dual extrusion) machines. Until I see people posting functional print projects with integrated multi material and dissolvable supports regularly, this is a pipe dream and deep dead end rabbit hole. I went down this one once already. Don't get fooled by anyone posting about some IDEX thing where they are showing off IDEX. The thing to watch for is complex problem solving where IDEX is not even worth mentioning because it is a mundane part of the design process. You don't see IDEX prints. Don't be fooled into thinking you are alone in this interest. Its absence is most telling about its effective application in practice.