Hello,
I noticed that the Z-axis leadscrews move quite a bit when the printhead traverses in X direction (left-right).
I checked with a straightedge and sure enough: the print-bed is severely bent - it has a 1-2mm bow upwards in the middle. Y direction is straight. The bend is pretty consistent front to back.
While the X1 Carbon compensates nicely for this bend and produces nice parallel layer, the objects I print all have this “banana” deformation. For small #bambutiful prints that might not be much of an issue but for bigger #bambuseful stuff this is a problem when the stuff does not come out straight. I exclusively print technical parts and had some alignment problems with the X1 in the past. Initially I thought it might be a warping issue but thing I have found the root of the problem with the bent print-bed. Is it possible to fix this or change the bed for a straight one?
Have you removed the sheet and see if the gap still shows just on the bed/magnetic surface?
No obvious bump or bugle in the magnetic surface?
good idea! or a bit of filament stuck on the underside of the spring steel sheet - that would be a classic.
but no - unfortunately that´s not the issue. see picture attached of just the “plain” bed without spring steel sheet.
Just open a support ticket. They may ask for a log file to check the latest bed leveling data.
I had a similar issue and after a short but nice discussion with support they sent me a new print bed.
Changing the print bed is quite a job to do, be prepared. 
thanks! will do that.
I have the same issue but then a dip downwards over the x-axis, the y-axis is straight. Did you get a new bed? And did that resolve your issue? Asking this because I’ve read on one of the Facebook Groups about Bambu Lab that the replacement beds also are not straight.
My replacement bed was perfectly straight.
I noticed the bed moving up and down while printing (on the same layer). I think this is the cause. Did you see that as well? It’s mostly noticeable while watching the live feed, the bed visibly moves.
This is how I first became aware of the problem. I saw it on the live feed and I discovered the constant movement of the rods during printing.
I had a long and friendly back and forth with support, was asked to do a firmware update, to perform manual tweaking with the nuts under the bed (Manual Bed Leveling / Manual Bed Tramming | Bambu Lab Wiki), send numerous log files but ultimately they only ever saw a variation of 0,2mm and I kind of gave up explaining the problem.
Here is a video (I also sent to support) showing the movement of the lead screws.
Bambu Lab bed bow - YouTube
To my understanding the screws have a pitch of 8mm and I see close to 45 degree movement (so that would be more like 1mm instead of 0.2mm.
I cannot really explain why I see so much movement on the screws, see a big gap between the bed and a staightedge but only 0.2mm show up on their logfiles. …other then the carbon rods are bent the same way - which they are not as far as I can tell.
anyhow: as I said, I kind of gave up and figured that the X1 is still a excellent printer for the money and I have other means of producing parts if I really need the precision. …and maybe it even is preferable to have a bow in that direction to counteract warping 
edit: wrote 4mm pitch leadscrews before - I have to check again when I´m home maybe they in fact don´t have 8mm - so that would cut the error in half. but still…
When I watch your video (nice idea with the clips by the way), I see a more or less constant movement. I wonder if this couldn’t be improved by manually levelling the bed. Then again, I’m pretty sure you’ve already done that…
I think no print bed is 100% straight, so there are tolerances that should be reasonable. 0,2mm is close to nothing and certainly acceptable, the question is why it doesn’t look like it.
I was doing some lubing yesterday and decided to level to bed manually. Now there is a lot less movement. But “non-level” is not the same as “warped”. But you can still “warp” the bed by having the screws very unevenly set so that one corner is much lower, I think (I haven’t disassembled it).
On that note, check your cable below the bed (on the rear side just behind the screw) - mine was rubbing on the screw and made a hole in the insulation (but no real damage). I moved it a bit and put some teflon tape around the screw and I am going to send it to support.
thanks for the heads up! my bed wire harness rubs against the back z axis screw too. nothing bad happened yet but definitely have to make provisions. really bad things could happen if the heating bed wires short out.
I actually wrote to support and got a not-very-satisfying reply: "The wire cover is added on the wires to ensure that the rubbing movement does not cause problems. "
I think they are missing the point that the “wire cover” (I think they mean the sleeve) is already rubbed through.
I sent them pictures and got: "The rubbing against the heatbed leveling knob should not cause any kind of problem during operation, so we believe that you can leave it as it is and it is safe to use "
I’m not convinced, so I will loosen the two screws and push the cable a bit further back to prevent the rubbing.
How would be possible to have the two front leadscrews counteract if they are on the same belt with one motor? See picture here: Z timing belt | Bambu Lab Wiki. Could you explain?
I just noticed the same issue on my X1 Carbon as well unfortunately. I was printing some large parts for the first time that were each part of a multi part assembly. All of the parts came out warped upwards on the ends (not acceptable or useable).
I reached out to support over the last weekend but haven’t heard back yet. I’m hoping they will help me get a replacement bed soonish because this was a time sensitive project.
For those in thr thread that got a replacement bed, how long did you end up waiting for the replacement and how difficult was it to replace the bed? The attachement points look fairly easy to get at but I could be wrong.
There is another (later) thread with a huge number of people reporting similar issues here:
…people mostly report concave print beds. Replacement beds seem to be warped too. Mine is convex. So mine might counteract errors to warpage somewhat. Another reason for me to give up on trying to explain the problem to the friendly but not very helpful support people.
Bambu Lab seem to be focusing on people that want to print multicolored spongebob figurines or gingerbread houses. I came to the conclusion that I have to use other means of production when I need bigger and/or precise parts. Its a shame but you can also only expect so much from a mostly injection molded printer at that price point. 