I now know that aluminium is unquestionably not suitable for the clamp plate. Why? Well, I tightened Ch6, the black channel, and 3 metres worth of test prints later, I had this superblob from Ch7, the copper channel:

Next month, I'll try and get them cut and tapped out of stainless steel. I can't find sheets, but I can find 5mm bar that should work for these 20mm wide mini-plates:

In the meantime, I've tightened the leaking channels just enough to feel resistance, trying not to tighten them such that the plate bends up. I then proceeded to print a combination of Ch1-4 for 1 metre to try and see what channels are leaking, and it doesn't seem like the max flow rate increases. This isn't much of an issue for the CR600S as 17mm3/s limited speeds paired with recently-calibrated 3600mm/s2 acceleration prints nice and snappy. 

I still need to calibrate M592, since my walls at this speed are 0.48 when they should be 0.68mm. Part of the 30% loss of filament could be attributed to leaks but it's unlikely.

I'd also like to mention that Ch3 clogged when I tried 36mm3/s feedrate, but unblocking was as simple as removing the part cooling fan, allowing 20 seconds for the heatbreak to heat up in the time it took me to send the command to extrude through the channel at 1mm/s. This provides additional evidence that a heater-controlled "valve" will prevent accidental backflow of unloaded channels. It should also mitigate clogs caused by heat creep in unused channels. For consumer-level reliability, it should be paired with a filament sensor so that the valve can only be turned on if the channel is both used and loaded.

Moving on, I wanted to see what my cooling performance was before I tried to redesign the front cover of the coaxial hotend. I set a print for a 1 : 1 mix of White : Black, but accidentally did Black : Copper. In any case, I stopped the print when it was obvious that cooling was inadequate. The only 45-degree overhang that came out good was the one directly in line with the cooling duct:

[Dec 30] I just remembered that I printed a temperature tower months ago, and considering the bridging difference between 236C and 218/224C, it's probably not helping that I was running this overhang test at 242C throughout. I'll just use 242C for bed adhesion and 224C for subsequent layers.

I've -- once again -- redesigned the hotend holder.

As you can see, the HolderTop plate has been split in two and the HolderBottom plate now allows the wires to go straight up. Unlike the first hotend holder design for Coaxial8or R0, the wires can easily exit the holder by removing the HolderFrontBack plate.

This design is closer to my vague, initial idea of what the holder would be like when I had the decision to change the Coaxial8or input arrangement, just that I thought that the two plates that hold the couplers would be directly connected to a "HolderTopConnector" plate instead of this arrangement. 

You may also notice the chamfers, and that's because I found a squashed thermistor wire when I went in to inspect for damage before embarking on more acceleration / linear advance / junction deviation tests.

I also encountered more leaks:

I reverted the directions of the extruders, now a lot easier without the washers, and printed a pancake with all channels and the print completed!

I finally figured out that 224C is too cold for the PETG to stick on the bed and had more success with 239C. During the print, I did hear filament slipping. I could then feel each of the filaments to find out which channel had the issue.

I wanted to see if the flow issues have been solved so I did another print in white. This had a few problems. 

The Z axis sounded like it might have skipped a step, and it showed in the print and had to babystep. I've now increased current from 0.6 -> 0.9A. Now that I'm typing this, I'm also considering increasing the Z_HOLD_MULTIPLIER (the current when the motor is not moving) from 0.5.

Additionally, I had set PrusaSlicer to move at a speed limited by 30mm3/s, but the channel choked and was only stable at around 40%, hence the expectation is 12mm3/s of flow per channel. 

I was also doing some in-situ linear advance testing to see if it was working.

During this print, I could see in the leak detection window some yellow that was coming out, which means that it's channel 2:

I could also see some transparent blue (and a little bit of white) eeking out of the output channel, so I cleaned this off and tightened at 220C:

After tightening the nozzle, I unscrewed the hotend and started to clean off the yellow before tightening its channel. It's nice to see that the leak channels work as intended.

As you can see, it looks like some transparent blue is also in there so I used needlenose pliers to try and tighten its channel. Unfortunately, the cartridge wire takes up more space than I expected, meaning that 2 of the 8 heatbreaks are unturnable by the wrench, and I'm thinking that a revision to the hotend holder could help fix this issue. It could also be cyan so I've gone around and tighened that too.

Now, since the Coaxial8or is out and in the open, I thought it was a good a time as any to heat to 240C and find the flow limit using this guide with the following changes:

• I used a crocodile clip from my hydra "helping hands" thing (seen in a previous log when it was holding the extruded filament)
• I used 112mm because that's the length of my screwdriver

The feedrate values I tried, in order were:

• 300 (worked, but probably doesn't count since the hotend wasn't fully pressurised)
• 600
• 450
• 360
• 330
• 300 (didn't work this time)
• 240 (worked)
• 270 (didn't work)

I then extruded 200mm through channels 2 - 8 with F240 as seen below. This corresponds to 240 / 60 * 2.4 = 9.6 cubic millimetres/second/channel.

There were no leaks to be seen. 

What's that? Big Leaka's stocks are tanking?

The flow rate is still disappointing though. I don't think there's even been a change over the previous designs.

[Next Day - 14:00]

I decided to set all motors to 900mA current, which should be in acceptable limits since the extruder motors are rated for 1000mA. Since non-moving extruders were perfectly fine, even way back at the start of the year when I set the run current to 450mA, I have also halved the default hold multiplier to 0.25:

Redoing the test at 240C, I was able to consistently extrude 300mm at F450 (7.5mm/s) through a 0.6mm nozzle, meaning that the volumetric flow has now increased to a respectable 18mm3/s per channel. The extruder motors are lukewarm.

[16:30] 

Decided to move past arbitrary limits and set 1A current for all motors. The steppers and the driver heatsinks are still barely warm, but the feedrate has increased to 510mm/min (8.5mm/s) for a volumetric flow rate of 20.4mm3/s. Since filament in some channels started to slip over the gears, I believe it's right on the edge and a flow limit of 19.2mm3/s should be used for printing. 

In other words, the Coaxial8or speed limit is 8mm/s with my present setup.

Some yellow is starting to creep out again so I need to further tighten it.

So today I did the following: 

• installed the fans
• installed the bowdens
  • trimmed the bowden of Ch 4 from 48 to 43cm
• heated the hotend and manually extruded the channels.

Ch 7 was the last one that I needed to do and it turned out to be the one to pop out, revealing that the input bowden coupling is merely just a friction fit. It seems like this coupling form over function; it looks nice but, as you can see, won't stick around for the long term. I never knew such a collet existed, but it could be useful if paired with a grub screw.

(Note: SANPrinter also goes by the name SANBrother)

These substantial looking plates are 5mm because it's the same thickness as the clamp plate and it's thicker than 3mm. If you remember all the way back to the start of the year, I had to use washers because of the DDEs (aka BMGs). Since I was planning on inverting the DDE's closest to the hotend, I thought I might as well correct my earlier error. 

The uni only happened to have M5 x 20mm bolts, so I used the M5x5mm brass insert strategy to "shorten" the threads to M5x15mm whilst undergoing the installation:

It was much easier to install the DDEs and they feel more solid/secure. I've been able to shorten the bowdens E0, E1, E6, E7 by 5cm, down to 30, 30, 30, 35cm respectively (about 14%). Additionally, it's much more ergonomic to reach the large gears on those extruders now.

Introduction

For the past few days, I've decided to work on the Coaxial8or project rather than write about all the things I should work on afterwards. I will say that I'm now deep enough into the project that I'm looking at the number 8 a little differently in day-to-day life, and those feelings manifested as a parody to Oscuro - Shake:

My bones still shake... when I hear:
8...
8...
8...
8...
(du do du do)
8...
8...
8, the endless
8...
8...
8...
8...
My bones still shake.

New aluminium print

The part came in a needlessly large box, and it certainly looks brighter than my previous prints:

The input seal bumps came out excellently, but the output was a little tilted:

Another thing is that the 6mm cartridge didn't quite fit.

CAD model changes

• Changed the cartridge hole back to 6.3 from 6.2mm
• Increased the cartridge gap from 1.5 to 2.3mm so that 2mm-thick files could fit.
• Increased the amount of material around the output seal bump, as well as increase the height from 1.2 to 1.5mm.
• Decrease the emboss angle of my logo from 45 to 30 degrees.
• Rotate the M6 thread 180 degrees. 
  • For some reason, PCBWay printed with the logo facing down, which is opposite to the screenshot they showed me. I can only imagine it's because they thought the thread would print better

Plates and tapping

I asked for a new hotend holder top / bottom to be cut out, since those are the parts that changed when I removed the side panels. I also asked for the clamp plates to be made out of both steel and aluminium.

Tapping the M4 thermistor grub thread as a bit of work but, by imagining the forces when the tool cuts the adjacent wall and accounting for them, I was able to tap just fine:

The seal bump seems to work as intended, providing a nice flat face by using the stainless steel nozzle. This is much better than having to flatten one massive face.

It does seem that the aluminium plate slightly bends up. So does the steel plate, but to a much lesser extent.

The steel plate cleans off with a few quick brushes of a file:

I tried tapping it the same way I've been doing it since R1, but the thread came out bent. I also tried free-handed tapping and it came out about as bent.

My hypothesis is that the cloner plate can slide out of alignment enough that it taps misaligned. I had further evidence when I tried to do the same with an aluminium plate.

I even tried tapping a steel cloner plate with no success:

I then tried an idea, inspired by the M4 thermistor grub thread, which was to use the vice to keep the up/down axis aligned and then I visibly check the left/right alignment:

This worked, and I was finally able to get a straight tap through steel:

Unfortunately, that's where the road will end for the steel plate. The above plate was just to use as practice, and it turns out that there was a divot in the other two plates that completely stops the tap from turning:

Thus, I used the aluminium plate to flatten the remaining inputs, which caused it to deform slightly:

I then tried to enlarge the cartridge hole, failing with a 6mm drill bit but succeeding with a 6mm reamer the uni just happened to have.

Fitting into the cover and carriage

It looked to fit well in the cover:

Unfortunately, the CAD model of the cartridge I downloaded from the internet was wrong and so the frontback plate touched the standoffs before the to / bottom plates could touch the x-carriage as intended. However, it was very stiff and reasoned that it was probably better this way since the frontback plate would always be relatively flat compared to the relatively misaligned top and bottom plates. I redesigned the holder.

30mm 160W cartridge

All the steps I've had to do took so long that the 30mm cartridges from AliExpress arrived:

I'd imagine they're old stock since no modern-day hotend would use these. They're also unmarked, but I took one out and it was 3.3 ohms. The ends are kinda dented-looking but should be serviceable. I had to be careful when stripping as there's only 7 strands in this red wire. 2 of them broke off when stripping for the first time, and after a heatup test, I decided losing almost 30% of my strands wasn't good enough. It's a good thing I checked, because I took the wires out of the quick connectors and there were only 3 strands standing!

I had the idea to install the heatsinks and then assemble the holder:

As it turns out, there wasn't enough space for the wires so I couldn't install the new holder. However, the Coaxial8or was able to heat up from 20 to 220C in 110 seconds with an unrefined fan mount and uncalibrated MPC, so I'm onto a winner here.

I should mention that I had to completely replace the thermistor because the old one is effectively welded into R2. I took this time to also trim down the hook-and-loop cable ties to 75mm to make them much easier to put on and take off.

Recutting the hotend holder

For engineers, the lyrics of XO-IQ - Get It Right will resonate:

Get. It. Right.
Do it all again.
This time round, I'll be better than.

Or, for actually trying to manufacture anything, a parody:

Get. It. Right.
Not do it all again.
This time round, it is better than.

Anyway, I actually had a new holder design. The reason why I tested the hotend with the older one was because the waterjet momentarily stopped working and the technicians were pressing buttons like game combos trying to rectify the issue. 2 days go by and the issue was resolved, and my parts were the first to come "fresh out of the oven":

As you can see, this design has space for the wires, and now holds the frontback plates from both sides. I think it's pretty elegant.

I had the idea of screwing the bottom plate to the top plate to keep it from flying around.

Currently, the best strategy seems to align 2 heatsinks at a time. The first 2 are rather easy, the next two are doable, and the 3rd set was rather difficult until I had the idea to use needlenose pliers between them and the 4th set:

The same strategy can be done for the 4th set:

Unfortunately, because of the wires, it was difficult to slide the frontback plates in. Thus, I've reduced the heights of the tabs:

Filing the cover

I didn't want to reprint the cover because it takes 4+ hours to print and there are issues with the design. I tried out the fan duct and there is much less airflow compared to no duct, and the trenches I allocated for the fan wires are needlessly small. 

I had to cut the top a tad and then use calipers to measure how much I had eroded away:

It took like 20 minutes once I got the strategy.

With this, I was able to install the c8or onto the cr600s.

So first the parts got cut out of the waterjet:

I then filled off the edges (with a large file) and deburred (with a small one), which takes a multiple more time than it takes the waterjet to cut the parts in the first place:

When all together, I could test and deduce that the Holder Side plates were useless and didn't bear any load whatsoever. 

Thus, I've removed the side plates from the CAD assembly:

The outer cover setup and print

Surprisingly, this turned into a multi-hour ordeal. Some of that was just getting one of the uni 3D printers to stick to the bed, but it was mostly to do with setup. 

I don't usually design parts that need supports, so I had to be setting that up. But then I'd get supports where I didn't want them, and Cura really doesn't like reloading a multi-body .3mf, so I modelled the no-supports zone in fusion. Additionally, I added a thickened section. I should've just done 100% infill instead of the 40% I set. 

Furthermore, as I was looking through the gcode preview, it did seem like there was a lot of excessive material being used so I trimmed it down. It also allowed me to catch an issue in the design, which is that I wouldn't be able to install one of the fans without first threading the wire through and resoldering.

It has then been printed, and the tree support broke away easily.

It does seem I overestimated how steep an angle I could print, which was 60 degrees. Instead, it seems that even 55 is slightly over the limit. I've changed a setting so that Cura prints from the inside outwards in aims of improving this.

The hotend holder design

I thought through a mental simulation and, like I mentioned in the previous log, I didn't have the confidence that the way I designed the side plate a few days back was going to work as intended, due to material bending:

Thus, I've opted for a 5th M3x12 bolt and dual side plates:

Clamp plate of R2

In anticipation of R3 and so that I can test the fit of the 6028 fans in the newly-printed cover, I disassembled R2. The reason why I haven't done much testing is that all the inputs were slightly leaking, as can be seen by the multicoloured  blob that remained:

Additionally, it seems that the elevated temperatures cause the top surface to rust. I couldn't see any rusting on the sides or bottom:

Like with last time, the strategy to separate and clear the heatsinks worked just fine:

1. Unscrew the clamp bolts
2. Heat to 150C
3. Use spatula to separate
4. Cool to 130C
   1. this prevents long, thin wisps and also allows for a "warm pull" of the inputs for the next step.
5. Pull clamp plate from Coaxial8or
6. Manually extrude material from each input till it pops out, after which the buldge can be snipped off and the filament recoiled.
   1. I did have to use needlenose pliers on 2 of the inputs to help them pop off the heatbreaks. 

Thinking of reversing the extruders that have shorter bowden tubes

The DDEs, more commonly called "BMG Clones", should be able to work when mounted in reverse. The benefits include:

• Much easier access to the large gear, especially for extruder E6 
  • (remember it's E0 - E7)
• The short bowdens will be even shorter
  • The drive gears are closer to the handle end of the DDE.
  • The improvement would be about 50mm or so, which will contribute a larger percentage difference for the 30-35cm bowdens of E0, E1, E6, E7 than the 45 -50cm of the others.

I decided to just go in and scribble something up for the fan duct. In my years of FFF printer upgrading, I've always dislike having to design them since they usually need to be more organic. To my surprise though, this duct came out better than I expected. It's effectively invisible from the front, giving the coaxial hotend assembly a very minimalistic and open look:

Design methodology

So I first decided that I was going to go back to the symmetrical-bolt mounting of the 6028 fans, and with the hotend holder now entirely made of metal, it can also help with heat dissipation. I then noticed that there'd be more space above than below the cooling 6028 so I pointed it upwards.

Then, similar to how I'd go about solving a maze, I started thinking up ideas on how the duct would start and end. I knew that the rear of the Coaxial8or was the most suitable location for the duct output. It also looked like a revolve would be beneficial to cool from multiple directions. I gladly found out that Fusion supports lofting from such a curved face:

I went on to refine the geometry so that it was at least 3mm or so from anything else and didn't stick out beyond the bottom wheel bolt:

I was finally able to model the new hotend holder, which uses aluminium plates for its construction. No longer do I have to worry about the holder unintentionally melting, sagging due to the weight, or blocking the view when inserting the heatsinks into the couplers.

This was one of those things that is kind of hard to model because when there's nothing but an empty canvas, it feels like every plate depends on every other plate, thus a cyclic reference (aka catch22 / chicken and egg problem). 

I initially was planning on a jaws-based solution similar to the redesigned holder for R2, but had concerns with grip so I just went with grub screws. This design allows all 8 heatsinks to get a grubscrew.