Full-colour FFF? Multi-materials with unparalleled interlayer bond strength? Abrasives without abrasion?
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Read more »I looked into the old-school all-metal heatbreaks and they use 3.2mm at the tube section. I believe I've also seen more recent hotend designs (like the SV08 in the previous log) use 3mm tube.
The issue I see at the moment is the sealing of the heatblock to the heatvalve. Perhaps they would have to be integrated too?
I'm not sure how far I'll get before all the additional manufacturing complexity nudges me over the edge to essentially say "Well, it was a good run, but that #SlimeSaver [gd0105] isn't solving itself and still has the optimistic appeal of potential performance." but I've currently modelled a potential heatblock candidate that is about 3.3 cm3.
At 7mm, the heatblock is 3.5 cm3.
I first designed the heatblock how I've always designed ones in the past, but it seemed to use more material than I'd like:
I then had the idea to use the Shell command to create the minimum-material-needed heatblock. Only the "rounded" type works anyway. The straight-edged shell would've used more material for little benefit:
Next, I proceeded to delete a few faces, add the dowel holder, and fillet things:
For the heater, an ideal solution might have been the clip Mellow came up with in their CHP hotend:
I don't think the clip alone is available, so I've modelled in geometry for a more traditional cartridge heater/thermistor, attached with nothing but boron nitride paste. They're not enclosed in part to save on material and to allow easy access of water to remove the cartridges if they need replacing.
D3D, in their listing for a hotend they sell, does seem to confirm my worries about thermal expansion on this press-fit solution. I'm not sure exactly how thermally conductive this heatblock actually needs to be considering all the twists and turns inside of it, so printing in stainless-steel is still looking the most ideal.
If anything, I might just take a page out of XYZDims and see if PCBWay or JLC can print 0.5mm thin tubes which I drill on the inside. I might have to ream too, but a rougher surface finish would both help with heat transfer of the filament and would actually turn the drawback of those pre-bimetal, chinesium all-metal heartbreaks into a feature by promoting "clogging" when the input is off. It might also save money both in material savings of the printed part but in thin-wall tubing too.
I was wondering if I'd need tolerances similar to the Tetoroidiv rotors and it seems like I do. Charts, machinist forums and Gemini all agree that, for a dowel 6mm or less, the "interference" should be 0.0005 of an inch for a press fit, though one forum-user was able to work with 0.001. In other words, the holes are between 12.7 to 25.4 microns smaller than the precision round object that's going into it. I also found the below video that recommended that the initial hole should be smaller by 70 - 140 microns for 1 - 3 mm holes respectively, meaning that for a 2.5mm reamer, I'd be using a 2.4mm drill to enlarge the roughly printed holes.
Now, since the rest of the world works in metric, the only options for reamers are 2.49 or 2.48mm. Gemini determined that 2.47 would be too much for a solid dowel pin, let alone a thin-walled tube. Speaking of the tube, my plan is to use 1.9 ID x 2.5 OD tube so that there is a tad less expansion space for the molten material and the tube walls give a little more strength than 2.0 ID.
2.49mm is closest to what all the forum-users are using, but Gemini and I did the thermal expansion calculations and the interference would loosen by 4 microns (aka 40%) when heated up to 250C and up. This isn't really an issue for copper, such as the Creality Unicorn nozzles, as both materials have rather similar expansion. I'm considering printing the heatblock in stainless steel from JLC since both the tubes and the cross-dowel pin is stainless steel. I know Dyze uses a non-stainless steel, and in the comments they said it was because of higher thermal conductivity. Obviously, as I've found out in this project, stainless steel is tough stuff.
I found some low-cost reamers and drill bits on AliExpress. I thought they'd be way more expensive. I'd have to spring for the coated ones from the other supplier I found if I go through with a stainless steel heatblock either now or in the future:
2.49mm feels a tad too close to the limit, especially since the whole system is pressurised too and there are 8 of these that need to be confidently installed, thus my first choice will be 2.48mm. There's also the option of lightly sanding down the tube if it's too small.
Allegedly, to actually insert the tube, I'll need something called an Arbor Press, which exerts forces measured in tonnes allegedly. I found a white, branded one that does 0.5 tonnes for around £50:
So I was wondering how I'd even know how much cooling was enough, and then I realised that the heatsinks I've got already were shown to work, implying that I just need a heatsink with similar surface area:
The faces exposed to air in the design are highlighted in blue. I then modelled the 22x8mm and 15x15mm heatsinks.
The price/volume is £4.52/487 mm^3 and £6.20/630 mm^3 for the 22mm and 15mm heatsinks respectively, so the price is proportional to the amount of copper.
I also found out about the RP1010, a 10x10mm ceramic heating element that comes in a range of resistances and only costs £5.50 for 5pcs. As you can see in the graph below, the 20 and 30 ohm options are suitable for 24V, which corresponds to 29W and 19W of dissipation respectively:
Due to the 15x15mm heatsink having a margin of additional cooling performance, the Flashforge heater is 15mm tall and this RP1010 is a square, it makes the most sense to use it for the next-generation Coaxial8or R4.
With my degree behind me, I'm soon going to lose the reason I attended in the first place: the manufacturing facilities. The good news is that, unlike back in 2016 - 19 when I went from 0 to 5 3D printers, there are quite a few outsource options in my league budget now that it's 2025; this fact is unlikely to stop my pursuit in 3D-printed multilayer boards seen in #SlimeSaver [gd0105]. The bad news is that I was scrolling Amazon, looking at all the nice FFF 3D printers, and then realised that none of them had a coaxialising feature:
I knew that if I was to engineer a 4th revision, it would have to achieve the following:
I did a bit of moving around of the inputs to take the 14mm CR-10 bolt locations into account:
Then I wanted to learn about how the tube is fitted permanently, and it just sounds like tight tolerancing, potentially using thermal expansion to their advantage during the insertion step:
Well, a thermistor is still stuck in the Coaxial8or R2 heatblock so I guess a straight hole really does work?
Looking at the Creality version, I'm going to assume I need at least 6mm inserted into the heatblock.
10pcs is about 15.5 cm^3.
I learned a bit about the KSD9700 and its suitability as bang-bang control of the heater. They are available up to 250C. Still, due to potential surge currents if all 8 inputs are active (though 4 at a time is much more likely), a more active control method may be required. This may also need a 12V supply since the ceramic heaters only come in 24V 50-80W options. I was planning to use the cylindrical ones, but then I realised that I'd be able to get the inputs closer together with the rectangular heating element.
The best heating element I've seen so far is the one for the Flashforge 5M (above) since the cable isn't too long (only 5cm), the thermistor is on the same connector (similar to a heated bed, for example), the heater is a not-too-extreme 50W and the whole thing typically costs less than other options for the heater alone (typically costing £18 for 10pcs).
The dimensions of the heating element are 15mm x 7mm. In a similar size, there's also mini copper heatsinks (below), so I may be able to acquire 16pcs of a part designed to facilitate heat transfer to/from the tube.
I still don't know precisely how I'm getting all of this attached, with boron nitride paste being the most likely option.
I went to research more about Flashforge hotends and I found this for the AD5X:
This is very insightful since it implies...
Read more »I had an idea and it turns out there is an off-the-shelf part that exists:
Coincidentally, it seems that M6 is the only option that even has a flange substantial enough to work.
Instead of having to carefully tap stainless steel threads for 90 minutes and still have them slightly misaligned, the idea is to have appropriately sized holes in a steel plate and the insert flange sandwiched between the plate and the heatblock. The insert is somewhat tall but I feel that it will be quick work to file them down.
As you may see from the image, the minimum spacing between inputs will grow to 14mm, but it's probably for the best. There's a bit more heatsink / bowden coupler options available when the spacing is above 12mm. For context, the Coaxial8or currently has 10mm spacing.
One of the goals for the next design will be to have the 8 inputs converge as near as possible, hopefully so that changes are faster. Thus, the input pattern may follow the Kobra 3 Filament Hub:
The aspect ratio is somewhat squarish though, which might not be ideal:
I was skimming through Marlin PRs and found this pull request on implementing a differential extruder:
This reminds me of when I had a similar belt idea for a cleaning roller in the SecSavr Suspense (which is currently named #SlimeSaver [gd0105]).
I'm thinking that this could allow for direct-drive extrusion for 3+ input hotends without the drawbacks of other methods such as a semi-stiff stick or mounting many heavy motors on the end effector.
If I understand correctly, I think this would even be Core XZ compatible, allowing all steppers to be in the base of machine like the Ender-3 V3.
So after spending some days wondering what to print (and finding out Orca will throw out all my settings if I open a .3MF with some,) I decided that I was going to tune scarf seams and M592.
I started off by learning the research posted in this guide on Printables and its comment section and applying it to a tesseract 3D model because "what point is a test print if you have confidence it'll print fine?".
I changed the z-seam location from random to aligned because some layers would try and start on an overhang.
I tested things like Inner/Outer vs Inner/Outer/Inner and, even with the latter looking questionable in the 90-degree overhang section (see below), I watched the print and came to the same conclusion that it's better.
I also set the bridge acceleration to 150mm/s2 which greatly improved the bridge actually anchoring to already-printed sections. I'll need to test more on a dedicated .STL in the future, but looking at the string left at the end of every print (as the hotend moves to the upper left corner over 20cm away), I think the strategy is low extrusion multiplier and low acceleration.
I tried a ripple cube STL I downloaded probably a dozen of years ago to see my current results on an easier print, and I had to turn off "Detect narrow internal solid infill" because it would try and bridge in midair:
I enabled Mesh Bed Levelling to help mitigate the first layer issues I had been having. I should've tried MBL out way earlier. A fade height of 3mm looked to be fine, considering my bed is only warped by 0.4mm.
I then moved onto this model to better see what the seams were doing:
I tested:
As I was printing, I noticed that my infill line wasn't starting all that well, and thought of an idea to test M592 Nonlinear Extrusion.
The yellow line is fullspeed, which should be 15mm3/s. This seemed to correspond to around 72mm/s, so I went up in units of 12mm/s for the other 5. For some reason, the slicer decided to print in the following order:
The fastest one was the only one that didn't quite start the extrusion right, but all of them had varying line widths from the start (blue dot) to the end of the line.
A bunch of trail and testing later and the results were inconclusive. I decided to rotate the pieces to give more time for the extrusion to equalise:
I just knew that I needed to do something about improving linear advance. One idea was a lower max e-speed in exchange for higher e-acceleration. When going into the tests, I had 120mm/s and 600mm/s2. I guesstimate to try 90mm/s, which was confirmed by using a calculator I found:
Dropping to 90mm/s, I used 0.9 k-factor to induce many E-movements and found that 3000mm/s2 worked but 3600mm/s2 had a slew of skipped steps. I then tried 0.45 and 0.6 and the latter was the best. This seems to agree with the setting found by an Ender 3 owner:
I was holding the filament during the print (to gather data on how the k-factor affected...
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Waw, that's great to hear! I do occasionally wonder if these logs are being sent out to a void as dark as this site's colour scheme, so it's reassuring to see this.
If you route a path in your AL and add a cover, water cooling. Probably lighter.
What do you mean by "add a cover"?
As for water cooling, I decided that I didn't want to include its complexity nor potential for leaks.
Oh.. I was just saying with your existing design you already have a nice block of AL right where you need cooling. Route a channel in the top for water to flow around and cover with a plate to contain it. Air cooling works too and is simpler, yes.
I have been following this project for months, and it's my go to morning reading when I clock into work, haha