Stealthburner build for the Switchwire
The toolhead is often the most complicated part of a 3D printer build, second only to ordering the right parts in the first place. A poor toolhead can differentiate a great 3D printer from a lousy one. Aside from the Zero, the standard hotend for Voron printers at the time of this writing is the Stealthburner.
While I've built two other toolheads before for the Zero -- the Afterburner and the Mini Stealthburner -- this was my first experience with the official one. As such, I was rather apprehensive going into the build because of all the complicated, fiddly parts I needed to manage. Surprising only me, the build turned out to be straightforward, even with several of the modifications I made to the design.
Unlike the Mini Stealthburner, a set of toolhead lights are a standard part of the full sized Stealthburner. I think the Mini also had them originally, as there's tell-tale parts on the fan cowl for them and routing channels for wires, but they aren't part of the Voron 0.2 assembly instructions. I plan to add them to the Zero in the future. For the full Stealthburner, you need to build a small chain of RGB LED ("Neopixel") lights using some thin, high temperature wire.
The power here isn't much, so we don't need a high gauge. I settled on some lengths of 30 AWG silicone covered wire, which only can handle 0.8A, but it has a temperature rating of 200C. Quite important near the hotend! I probably could get away with 80C rated wire, but silicone insulated wire is very flexible, which is essential in the tight space of the fan cowl.
The thin wires combined with the neopixels were nerve wracking. I still remember how frustrating it was to solder all the LEDs on for the Helix keyboard I built years ago. I ended up ruining so, many, LEDs, in that build and spent hours trying to fix them all. Eventually, the entire keyboard failed and I replaced it. Likewise, I was worried about pulling or breaking all the thin wiring. I recently had to rewire the Zero's toolhead because of failed wires for both blower fans.
Since it worked well during the Voron Zero build, I put on an audio drama and started work. The hardest part turned out to be getting the wire lengths right. I was going to complain that the Stealthburner Assembly guide didn't include the lengths, but it turns out, it did! I really should have brought down my laptop to the basement workshop instead of relying on my tiny phone screen; maybe then I would have noticed the lengths were all spelled out. Some careful filing and fitting later, I managed to get all the lights installed.
For this build, I decided to use a two part toolhead PCB instead of wiring everything directly to the mainboard. One thing I've learned from the Zero is that I want to build to repairability if at all possible. Parts should be easily removable, and components should ideally be tested independently of the printer. The fan cowl half of the PCB is little more than a point for easily connecting the lights and fans to a pin header which connects to the secondary PCB. Still, it makes the wiring very clean. The fans were easily tested with a bench power supply set to 24V. The LEDs however...
I stressed about this for a good few days before I decided to test them. Unfortunately, I didn't have any Arduinos handy any longer -- they were all used in other projects! I did, however, have a pair of Raspberry Pi Pico boards. After a bit of research, I landed on a handy tutorial which uses CircuitPython to light up a chain of neopixels. The tutorial was, in fact, part of a series of tutorials on using CircuitPython and the Pico.
The difference compared to the Arduino was night and day. Instead of an odd, C-like syntax, the code was plain Python. Instead of a specialty IDE, you write a text file to the micro, which when connected, looks like a USB memory stick. The process was surprisingly pleasant. Some quick firmware installation and coding later, I could test the lights.
And seeing all those pulsing rainbows made my little gay heart sing.
I've been trying to use the term toolhead to refer to the collective assembly of the extruder and hotend throughout this post. While it's more conventional to refer to them all as a "hotend" in the 3D printing world, CNC machine users tend to the latter.
Drawing again from experience from the Voron Zero, I decided I wanted to try the new Revo hotend for the Switchwire. While the Dragon is an excellent hotend, it's designed around a conventional nozzle, heater block, and heatbreak design. The Revo combines the nozzle and the heatbreak into one unit, which eliminates the potential for gaps which can mess up the hotend. If the extruder becomes jammed, it may be easier to clear by simply removing the entire nozzle-heatbreak instead of a time intensive toolhead disassembly. The integrated thermistor and heater coil on a self-tensioning spring is a nice touch.
The downside is that this system is patented, and it'll be harder to find replacement parts for it without paying whatever E3D wants. That may be worth it for now, since I rarely change nozzles as it is and tend to use them until they completely wear out (and often a little past that). Fortunately, the Revo is only one such choice for the Stealthburner; in theory I can swap it out for something else if I so chose.
The Clockwork 2 extruder was almost as intimidating as the LEDs. For some reason, the pure mechanical nature of it was more an exercise in patience for me than fear and stress. Careful filing and fitting of the parts required a couple of hours of work before things all seated together and fit smoothly.
Like with the Mini, I used a length of nylon cleaner filament as a test strip to see if the gears were working properly. Unlike the Mini, I had no problems with the recommended extruder parts fitting properly or having any sort of run-out I needed to correct. I made the questionable decision to buy a hardware kit for the Zero instead of buying all the parts individually, and the knock-off extruder parts weren't the best in that kit. The ones I got for the full Stealthburner fit without issue after filing the 3D printed parts to size.
Since there's no other place to put it, the extruder is also where the other half of the toolhead PCB is mounted. Two small threaded inserts and a small spacer part are needed to mount it, and are part of the standard Stealthburner build even if you don't use the PCB. Mounting the board is harder to explain than to do in person; place bolts through the board, place the spacer on the underside of the board through the bolts, and screw it into the rest of the extruder.
Again, I thanked my experience with building the Voron Zero here. I had took the time then to teach myself how to re-terminate JST and Dupont style connectors and that experience was invaluable here. I managed to get the cable for the motor sorted with few issues.
Re-terminating the Probe cable for the Z axis endstop, however, was a little more frustrating. I had trouble getting the JST connector pins to work properly and ended up having to redo one a couple times before I felt satisfied. In retrospect, I should have removed most of the thick insulation on the cable instead, making it easier to work with. Eventually, though, I got that plugged into the PCB too.
I think one of the lessons I learned during this part of the build was that building self-contained subassemblies is a design aspect I really like. With the Stealthburner, I can break down the entire toolhead into three parts: fan cowl, extruder, hotend.
I also really like the idea of testing each part independently -- like a Unit Test, only for a physical machine. The fan cowl was easy enough with a properly programmed microcontroller and a bench power supply. The extruder is mostly mechanical, but the extruder stepper motor has yet to be tested. In theory, it can be done with a proper driver board and a microcontroller. I even got the driver board! I have yet to actually test it though... The hotend would require something more like a mainboard to power up the heater coil and test the thermistor. That may be worth doing at some point, but it's often the part which has the least problems out of the box. It either heats, or it won't.
There's also a balance to be had with testing subassemblies. It may be worth it for "high failure" parts (like the LED and fan wiring) but less likely on stepper motors and hotend parts. At some point, you just need to do an integration test and power up the printer.
Speaking of power, that's what we'll be working on next for the Switchwire.
