Another wild ride over the past two weeks! As mentioned in the last update, assembly continued and I started running into a few major collision problems that only became apparent once everything was physically bolted together. CAD is one thing - but a real printer is another, especially if you don't measure every part yourself and accidentally forget a few important screws in the CAD model.
The good news: everything is fixed & the Printables files are now updated through Step 6: Nextruder assembly, so everyone following along can download the files for building. But getting here was definitely a journey.
There were two major problem areas: The first was the rear Z-axis screw guide. It was derived from the CORE One L design and ended up colliding with both the mounting screws of the trapezoidal nuts and the bed carrier.
The second was the fan shroud. I initially reused the CORE One L part, but during full travel testing it collided with both the rear bed cable cover and the alignment pins on the Prusa MINI heatbed.
Naturally, a few people asked whether this was simply a height issue that could have been easily avoided: Well ... yes and no.
It's really the result of several seemingly insignificant geometry differences that all stack up around the print bed - differences I simply hadn't accounted for, because i did not look at the right spots.
After digging into it, I found the following:
The reference geometry in Prusa's official CAD isn't always identical to the real hardware - especially the cable cover is a mashed together mess of multiple intersecting parts. The spare part model is accurate, but while designing the rear cable cover I used dimensions from the assembly CAD instead.
The smooth CORE One print sheet is noticeably thicker than the satin Prusa MINI sheet I'm using. The thicker PEI alone already adds some height, which gives a bit more clearance.
The Prusa MINI heatbed is only 2 mm thick, while the CORE One bed is 3 mm.
Additionally, the MINI heatbed alignment pins are 4 mm long instead of 3 mm.
Finally, the CORE One L fan duct sits roughly 0.9 mm lower and is angled slightly differently because the C1L doesn't have the rear cable cover and its fan is mounted lower.
So none of these differences are particularly large on their own. Together, however, they created collisions almost everywhere on the rear side of the print area. Depending on where you measure, I was off by somewhere between 2 mm and 3.5 mm.
The good news was that nothing fundamental was wrong with the design. The bad news? It took me a while to figure out why everything was crashing into everything else.
This one was fairly straightforward: add reliefs for the screw heads, change the rear angle and shift the bearing position slightly so it sits perfectly flush with the rods. "Straightforward" still meant five printed iterations before I was happy.
Once I understood where all the height differences came from, these were relatively easy to redesign. One unexpected consequence was that the original M3x10 screws became too long and could contact the metal bed carrier, so they had to be replaced with M3x8 screws.
Originally I hoped I could simply reuse either the CORE One or CORE One L duct. Unfortunately, after quite a few CAD experiments, that became impossible without moving the chamber fans - and I wasn't willing to redesign the entire printer around a single part.
I tried just about everything: lowering the mounting points, adding clearance bends at the rear, slightly tilting the duct, creating a hybrid between the CORE One and CORE One L designs and even rotating the original duct by about 5° and designing an adapter. None of those solutions really satisfied me.
Since I absolutely despise surface modelling, this ended up taking much longer than expected. In total, the fan shroud went through eight iterations before I finally had a version that cleared everything (except the pins) and still looked like it actually belonged on the printer.
This was probably the hardest decision, since it required physically a genuine part that does not really need to be modified. In the end, I still shortened the Prusa MINI Heatbed alignment pins by 1 mm so they match the CORE One geometry.
Could I have designed around them? Sure. But the project at this point isn't intended to be a bolt-on assembly kit - it's a custom DIY printer. At this point it simply made more sense to modify a standard part instead of spending a few hours fighting surface modelling for a tiny gain.
While waiting for yet another round of fan shroud prototypes to finish printing, I also started working on the firmware. I decided to fork the pre-INDX-stage of the Buddy Firmware, to have a more easier to approach playing field. So there's now an experimental firmware that defines the new motion limits + a few other things.
Current Motion limits are : 184 × 191 × 205 mm (technically we would have 207 mm on Z due to the thinner MINI bed + a bit of wiggle room for the print sheet). The build volume is 180 × 180 × 200 mm - so we are reaching the design goals here :)
And before you asked: yes ... the printer finally performed its first extrusion, the first (proper) prime and a few first layer tests. I spent quite a bit of time running first-layer tests to verify probing accuracy and bevore before that, intentionally drove the toolhead manually into every possible corner of the machine to make sure no collisions remained.
At first I still found a few - the aforementioned bed cable cover in the back - now they're finally gone.
At the moment I'm refining the filament sensor and redesigning the side handle. Due to the limited space, the sensor protrudes into the handle cavity. I'm also finishing the spool holder so it properly fits the Prusa USS Drybox.
There are still a few grey prototype parts on the machine that need to be replaced with the final black or orange parts ... but we're getting very close.
In case you're wondering why it takes so long to assemble the final pieces even though everything is already designed: it's because I'm creating a complete BOM in parallel while also making sure every single part is fully tested, has the correct geometry, and fits the actual machine. Patience is key here - I don't want to release a project that's full of little issues.
So, in short: motion is working, the mechanics behave exactly as intended and all remaining clearance issues have been ironed out. That means I can continue the assembly and finally move on to actual print testing.
Before I wrap this update up, I just want to say thank you to everyone following this project.
The encouraging comments, excitement and positive feedback over the past months have honestly helped a lot. Projects like this always have moments where things don't go as planned and it's easy to spend hours - or even days - trying to solve what turns out to be a tiny geometry issue.
Seeing people genuinely interested in the project and looking forward to the next update has been a great source of motivation to keep pushing through those setbacks.
So, thank you for sticking around and following this little adventure. I really appreciate it. On to the next milestone.
If you want to learn more about the project, make sure to checkout the main post "CORE One Mini - The Rocky Road to a Prototype." for the complete background and FAQ.
If you intend to buy a Prusa machine, you can use the referral code "@suit" at checkout in the Prusa online shop. This will give you some Prusameter points and 1 kg of free filament and i'll get some points aswell (which I can use for some free filament). Or you can just download, like and make some of my models here on Printables and even consider to become a member in my Printables club.
I've also set up a GoFundMe campaign to tackle the costs. Thanks to everybody who has donated to the project euros already - that means a lot and helps me cover the expenses.
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