Stop at the top.
Hallo zusammen, ich habe eine Frage. Ich bin gerade dabei, die vorderen Führungen zu modifizieren. Die hintere Führungsmutter wird durch den Bettanschlag begrenzt. Meine Frage ist also, sind die beiden vorderen Führungsmuttern auch nach oben begrenzt oder treffen sie auf die Oberseite? Danke und liebe Grüße aus Hamburg.
RE: Stop at the top.
Not quite sure what you are asking. In the fully assembled printer, vertical travel of the heatbed is limited by the nozzle of the printhead touching the bed.
In my Core One there is a remaining distance of approx. 6.5 mm between the POM nuts and the upper guides of the front leadscrews when the nozzle touches the print sheet. (Using the stock nozzle and print sheet.) The rear POM nut actually comes a bit closer to its end stop, maybe leaving a 4.5 mm distance. Both distances are measured to the upper side of the actual POM nut, not the screw heads which hold it in place.
RE: Stop at the top.
Hello Jürgen, thanks for your reply. I haven't finished assembling the printer yet. I've added guide nuts with play compensation, and as a result, I need some space above, hence my question. After seven "normal" Prusas, you have to rethink which parts move 🙂 Thanks for your effort.
RE: Stop at the top.
What play is there to compensate?
Vertically, I think the heatbed's weight pushing it down is enough to take out any potential play. Laterally, all that matters is that the positions of the linear bearings and the POM nuts agree while the bed is in its bottom-most position. The lead screws are only mounted (via the motors) at the bottom, and can tilt and flex because the motors are on flex mounts. So non-parallel lead screws are not an issue, and the nuts don't need to accommodate them.
RE: Stop at the top.
Hello, I also think that the weight is sufficient. That's where I come in as a toolmaker with a penchant for perfection. I get the reference below directly from the base plate and not from the screw heads. I also level the bed using springs. I don't really like the solution with the two 8mm shafts either. 10mm shafts will be added in the future and I'll also build a guide shaft in the back. I don't like the fact that the whole system rests on the motor at the rear. Enough, this is getting inappropriate for the novel 🙂 . Thanks for your time.
RE: Stop at the top.
Why change something if there is no problem? Especially if the machine has never run before?
RE: Stop at the top.
Hello, I also think that the weight is sufficient. That's where I come in as a toolmaker with a penchant for perfection. I get the reference below directly from the base plate and not from the screw heads. I also level the bed using springs. I don't really like the solution with the two 8mm shafts either. 10mm shafts will be added in the future and I'll also build a guide shaft in the back. I don't like the fact that the whole system rests on the motor at the rear. Enough, this is getting inappropriate for the novel 🙂 . Thanks for your time.
The heatbed will always rest on the three motors; the smooth rods only provide lateral guidance. And two rods already over-constrain the bed laterally, so I don't see the benefit of adding a third rod. In fact that might be harmful, increasing the risk of jams by adding two more redundant constraints.
RE: Stop at the top.
Hello, I also think that the weight is sufficient. That's where I come in as a toolmaker with a penchant for perfection. I get the reference below directly from the base plate and not from the screw heads. I also level the bed using springs. I don't really like the solution with the two 8mm shafts either. 10mm shafts will be added in the future and I'll also build a guide shaft in the back. I don't like the fact that the whole system rests on the motor at the rear. Enough, this is getting inappropriate for the novel 🙂 . Thanks for your time.
The heatbed will always rest on the three motors; the smooth rods only provide lateral guidance. And two rods already over-constrain the bed laterally, so I don't see the benefit of adding a third rod. In fact that might be harmful, increasing the risk of jams by adding two more redundant constraints.
Btw., my Front-Right Z-Axis leadscrew resonates a lot, when the bed is moving down at the end of prints.
I loosened the POM disk until it started to move in XY, but had no play in Z and it fixed it.
I also tried to move the bed a bit up and down, then tighten the POM disk with the bed at the bottom, middle or top, but the noise was always the same.
Lubricating would probably be the way to go, but since my Z-axis works flawlessly, I guess it's okay as it is.
However I'm thinking about taking one of the Z-rods out, but I'm not sure if the bed would rotate a little in XY, causing inaccurate prints..
RE: Stop at the top.
However I'm thinking about taking one of the Z-rods out, but I'm not sure if the bed would rotate a little in XY, causing inaccurate prints..
I wouldn't do that -- as you say, without the second rod the heatbed will be under-constrained and can rotate around the first rod. If the leadscrew at the "no rod" position wobbles a bit, it will induce that rotation whenever it moves to do the software-compensated bed leveling.
With both rods in place, they will indeed over-constrain the system and could potentially causing jams. (The theoretical optimum would be one rod in a circular bearing and one rod in a slot, restricting 2+1 degrees of freedom. But "precision ball-bearing guide slots" are not a thing, so this is not a very practical solution.)
There is no way to adjust the two rods to be precisely parallel, unfortunately. I think the best you can do is to loosen and re-tighten the left and right bed mounts while the bed is at medium height. By adapting the mounts to the rod distance in the middle you strike a decent compromise and should minimize the potential strain on the rods and bearings.
RE: Stop at the top.
Hello, I'm always striving for the highest level of perfection. This is certainly due to my training, where I was often used to working to less than 0.01 mm.
That's why I also build and stiffen the frame with a lot of carbon fiber for maximum stability. This way, my printers print with an accuracy of about +- 0.03 mm. I know it myself, it's a bit crazy 🙂
RE: Stop at the top.
Definitely cool stuff, and beautifully executed!
But I remain skeptical of an approach which first tosses additional, redundant constraints into the mix, and then requires super precise parts to make the over-constrained design work. And I would be reluctant to replace steel parts with carbon fiber parts in parts where they see large temperature swings. I believe Prusa deliberately used steel for all larger structural elements in the Core One, to keep thermal expansion coefficients consistent throughout.
RE: Halten Sie oben an.
I completely agree with you. I don't see any need to modify the frame in the Core One either. Apparently, the plastic rivets are sufficient. I'm curious to see how this turns out. I'm finishing the build now and will see how accurate it is. In any case, thanks again to everyone.
RE: Stop at the top.
I would finish a complete stock build and get the printer running first - then modify as and how you wish later, knowing you have a good baseline starting point.
RE: Halten Sie oben an.
Hello, so I have the core ready. All mechanical elements are elaborately aligned with suitable measuring means. Everything therefore runs cleanly and easily. The often described vibrations are also noticeable with my printer and therefore I take them as a given. I made the print bed on approx. Z=80mm aligned over springs with a measuring clock. So far so good. Now comes the big but !!!! Since the 3 Z motors cannot be calibrated individually, the bed is already moving significantly above the 80mm travel distance. Surely this compensates for the most part the software. With 2 engines I did not observe this so much. Perhaps in the future there will be a possibility to intervene here on the software side. You a trouble-free print