RE: Prusa CORE One kit assembly instructions
In steps 4.31 and 4.32 of the assembly instructions, the trapezoidal nuts of the front Z lead screws are bolted to the heat bed assembly before the vertical smooth rods are installed. That seems quite wrong: It's the smooth rods which will define the lateral position of the heatbed. The screw holes of the trapezoidal nuts do indeed provide a lot of lateral play, so they can align with the position defined by the smooth rods -- but if you bolt them down without the smooth rods in place, you don't know the right position.
The way Prusa describes the assembly, they let the lead screws define the lateral position, and then the smooth rods are "jammed in" later, potentially under significant mechanical stress. I wonder whether that's how they build the assembled units, and whether that is the reason behind the reports of some Z drives jamming up? Lubricating them may just be a workaround then, not fixing the root cause.
I have inserted the smooth rods before tightening the screws on the trapezoidal nuts, which should ensure everything is aligned without tension. Added a comment suggesting this to the build instructions too.
RE: Prusa CORE One kit assembly instructions
From a mechanical point of view, this also seems to me to be the more logical option. The position of the nuts should be determined by the guides and not vice versa. Thanks for the information.
RE: Prusa CORE One kit assembly instructions
After mounting the core x y assembly I noticed one of the belts (teeth side) being in contact with the zip tie that holds the cable of the thermistor at the exhaust fans. Everything seems to be aligned correctly.
I worry that either belt or zip tie will wear off eventually.
Does anyone of you have the same issue?
I'd be making sure that you sort this out before continuing with your build. Can you rotate the cable tie to make sure it is away from the belt? If possible maybe use a thin piece of velcro to secure as it will be less bulky.
Scott
RE: Prusa CORE One kit assembly instructions
Theyll likely be laser cut, then folded on a press brake. Depending on the operator who folded them, very accurate way of doing it.
I miss my days of operating a laser, but maybe my g-coding from those days might come in handy for owning a 3D printer 😅
Good to see your progress coming along nicely, now hurry up and finish it for God's sake 😂
Scott
As many as they are making I doubt they are hand bent, they most likely have a stamping die to bend them.
Possibly, but they're only 2 per printer. We used to batch form hundreds of parts at a time, sometimes simultaneously L+R handed to speed things up. It's not out of the realms of possibilty imo. Also considering the amount of parts formed for the core one it would make sense that a press brake or two be utilised. Anyway, where's my printer kit? 🤣
RE: Prusa CORE One kit assembly instructions
General recommendation: With hindsight, I wish I had prepared a large sorting box for the screws and nuts. There are about 30 different types of more-or-less common fasteners, and the number of times I have sorted through little baglets inside larger plastic bags is getting annoying...
My own fault entirely. Now that I am about halfway through the build, some of the little bags are already empty and I am too lazy to get better-organized. 😉
RE: Prusa CORE One kit assembly instructions
General recommendation: With hindsight, I wish I had prepared a large sorting box for the screws and nuts. There are about 30 different types of more-or-less common fasteners, and the number of times I have sorted through little baglets inside larger plastic bags is getting annoying...
My own fault entirely. Now that I am about halfway through the build, some of the little bags are already empty and I am too lazy to get better-organized. 😉
What came first the 3D printed sorting tray or the 3D printer 🤣
RE: Prusa CORE One kit assembly instructions
Oh, and another tip: If you have an M3 tap (thread cutter) in your workshop, have it ready. The Core XY assembly relies heavily on M3 screws cutting their own threads into plastic parts. All axles for the idler wheels are mounted like that, plus a few other instances. Feels a bit cheap, probably works alright, but is annoying to assemble: Getting the screws to start the thread, and do so while sitting at a right angle, is fiddly.
Cutting the first few turns of the thread with a tap makes life much easier. Don't cut any deeper; we probably want the screws to sit tightly (without play) in the threads they cut for themselves.
RE: Prusa CORE One kit assembly instructions
After the X rail has been mounted onto the Y rods (step 5.35), there is surprisingly no step suggested to fine-tune the distance of the Y rods. At this point, the Y rod distance will be arbitrary (within the tolerances given by the screw holes); it will not match the distance of the linear bearings as defined by the X rail.
It's easy to do, with the XY frame turned over: Loosen the screws which hold the front and back mounting blocks for one of the the Y rods; move the X rail back and forth to nudge the Y rods to the correct distance. Lightly tighten the screws; push the X rail back & forth once more. Fully tighten the screws, done. The X rail moved noticeably easier in my assembly after this adjustment.
RE: Prusa CORE One kit assembly instructions
After the X rail has been mounted onto the Y rods (step 5.35), there is surprisingly no step suggested to fine-tune the distance of the Y rods. At this point, the Y rod distance will be arbitrary (within the tolerances given by the screw holes); it will not match the distance of the linear bearings as defined by the X rail.
It's easy to do, with the XY frame turned over: Loosen the screws which hold the front and back mounting blocks for one of the the Y rods; move the X rail back and forth to nudge the Y rods to the correct distance. Lightly tighten the screws; push the X rail back & forth once more. Fully tighten the screws, done. The X rail moved noticeably easier in my assembly after this adjustment.
I have already asked myself whether such a point exists in the instructions. Screw on one side and the opposite side should align itself parallel to the fixed side. That's how it should be and that's how I intended it to be. But for anyone who doesn't know much about mechanical engineering in general or guide rails, your tips are definitely very valuable! Thanks for that.
RE: Prusa CORE One kit assembly instructions
Oh, and another tip: If you have an M3 tap (thread cutter) in your workshop, have it ready. The Core XY assembly relies heavily on M3 screws cutting their own threads into plastic parts. All axles for the idler wheels are mounted like that, plus a few other instances. Feels a bit cheap, probably works alright, but is annoying to assemble: Getting the screws to start the thread, and do so while sitting at a right angle, is fiddly.
Cutting the first few turns of the thread with a tap makes life much easier. Don't cut any deeper; we probably want the screws to sit tightly (without play) in the threads they cut for themselves.
From the build instructions, it looks like most of the rollers have a screw through the center of the bearing. Will it rotate on the screw or is it locked in place somehow?
MK4S/MMU3
RE:
From the build instructions, it looks like most of the rollers have a screw through the center of the bearing. Will it rotate on the screw or is it locked in place somehow?
There is no dedicated locking. I think they are just relying on the belts pulling the idler against its screw axle, and the resulting friction holding the central part of the bearing in place. The bearings will move more easily than the screw/center hole fit, so I would expect the central part of the bearing to stay put. But you are right, it's a bit "dirty".
RE: Prusa CORE One kit assembly instructions
After mounting the core x y assembly I noticed one of the belts (teeth side) being in contact with the zip tie that holds the cable of the thermistor at the exhaust fans. Everything seems to be aligned correctly.
I worry that either belt or zip tie will wear off eventually.
Does anyone of you have the same issue?
Yes, it's the same in my build, and I don't see how anything could be aligned differently. I have just removed the zip-tie again; don't think it is needed -- once the printer is assembled, nothing is tugging at that cable.
Thank you for spotting this! Now wouldn't it be nice if you had identified the cause of the belt ripple/VFAs in the Core One? 🙂
Wishful thinking probably; I don't think it is the likely cause.
RE: Prusa CORE One kit assembly instructions
After mounting the core x y assembly I noticed one of the belts (teeth side) being in contact with the zip tie that holds the cable of the thermistor at the exhaust fans. Everything seems to be aligned correctly.
Yes, it's the same in my build
Maybe I wrote too early: The belt will move in a bit when properly tightened. But it remains an awfully close encounter; if the belt should oscillate slightly, it will touch the zip tie again. I will continue to omit the zip tie.
RE: Prusa CORE One kit assembly instructions
There is no dedicated locking. I think they are just relying on the belts pulling the idler against its screw axle, and the resulting friction holding the central part of the bearing in place. The bearings will move more easily than the screw/center hole fit, so I would expect the central part of the bearing to stay put. But you are right, it's a bit "dirty".
I wonder if the play between the bearing bore and the screw threads contributes to the VFAs.
RE: Prusa CORE One kit assembly instructions
Having thought about the kinematics more, that play is an unlikely source as long as the bearings are functioning properly.
RE: Prusa CORE One kit assembly instructions
Going to slacken the trapezoidal nuts on my prebuilt printer then tighten them again.
Also can someone take a picture of the 4 new feet as my printer came with the foam strips.
Normal people believe that if it is not broke, do not fix it. Engineers believe that if it is not broke, it does not have enough features yet.
RE: Prusa CORE One kit assembly instructions
Going to slacken the trapezoidal nuts on my prebuilt printer then tighten them again.
Also can someone take a picture of the 4 new feet as my printer came with the foam strips.
Good idea to re-seat the trapezoidal nuts. You may also want to loosen the screws which hold the complete printed parts that carry the linear bearings and trapezoidal nuts to the bed assembly (steps 4.31 and 4.32 of the build instructions). The distance of the two smooth rods is over-constrained as well, by their supports in the printers base and by the linear bearings on the bed. Re-tighten those screws first, then tighten the screws which hold the trapezoidal nuts. All with the bed in the bottom position, of course.
The new feet are shown in step 2.16 of the build instructions, second picture:
https://help.prusa3d.com/guide/2-base-assembly_835498#838996
RE: Prusa CORE One kit assembly instructions
Most annoying assembly step for me comes towards the end: Bolting the orange handle and the filament sensor to the right side panel (step 7.37).
Three loose parts get connected at once, with a single pair of screws connecting all three. Because the filament sensor sits in a tight space, the side panel can't be attached to the frame yet, but is dangling outside, connected by the (short) teflon tube on the inside. I found it difficult to eyeball whether I had positioned the filament sensor correctly, because you don't have good line of sight and the parts sit at a non-intuitive position due to the slanted wall of the side recess.
Get somebody to help hold that side wall in place during that step, and to help with eyeballing from different angles. Going forward, Prusa could make life easier with a slight design change to the filament sensor body: Add little recesses around the screw holes to give tactile feedback when the screw tip has found the hole.
RE: Prusa CORE One kit assembly instructions
Most annoying assembly step for me comes towards the end: Bolting the orange handle and the filament sensor to the right side panel (step 7.37).
Three loose parts get connected at once, with a single pair of screws connecting all three. Because the filament sensor sits in a tight space, the side panel can't be attached to the frame yet, but is dangling outside, connected by the (short) teflon tube on the inside. I found it difficult to eyeball whether I had positioned the filament sensor correctly, because you don't have good line of sight and the parts sit at a non-intuitive position due to the slanted wall of the side recess.
Get somebody to help hold that side wall in place during that step, and to help with eyeballing from different angles. Going forward, Prusa could make life easier with a slight design change to the filament sensor body: Add little recesses around the screw holes to give tactile feedback when the screw tip has found the hole.
I've disassembled and reassembled it so much time that it became a breeze to me ahahah, but yes it's quite annoying...
RE: Prusa CORE One kit assembly instructions
Duh -- I managed to botch the very last assembly step, sticking on the door handle. Paid so much attention to the vertical alignment (which the instructions call out) that I did not push the angled metal fully against the door pane. And then quickly realized that you get only one attempt: Even if the adhesive has not been pressed on yet, you can't pull it off again; it will rather rip apart the foam tape. Strong stuff!
Remembering the "My door handle fell off!" thread, I decided that this was an opportunity to do it properly and screw-mount handle right away. There are two convenient pairs of holes in the handle and the door, and enough spare screws and nuts in the kit, so my handle is firmly attached now. But one of the screw heads touches the printer's frame, so I will have to switch to counter-sunk screws eventually. I will do that as soon as I have confirmed that I will keep the printer; don't want to take a countersink to the metal part just yet.
So, when you build your kit, be smarter than me at that step: Either pay proper attention and get it right first time -- or if ends up slightly off, don't be a perfectionist and try to peel it off again...