VC4 400 Both back corners dip
The mesh range is less than 200um, so it would probably work without any changes. However, I would like to understand what could be causing this dual dip. Or perhaps, why does the x-gantry seem to bow more at the back than what it bows in the front? Tried re-tensioning the y-rails, and also tried making sure the y-rails run parallel by moving the gantry before tightening the screws. Seems the y-rail re-positioning/r-tightening had very little effect. This perhaps could be explaind if the y-rails/extrusions had a slight turn (like in a screw or a drill, I am sure there is a proper term for it..) in them, so that the x-rail gets bent slightly differently at the back vs. in the front. Any ideas on how to understand what is going on, and how to fix it? Twist the extrusions along their longitudinal axis with some yet-unknown method..?
80 Replies
This is your X gantry bowing down
The bow on the back
Is because of that actually.
Since your z tilt works that way
This usually goes back to back
Since your Z1 is high because of the X gantry
It actually lowers the back in whole
And then you get that slope
From front to back that goes
I do not think that is exactly how it works 🙂
Well then I can't help you, I've got a bed variance of 0.07 on my vcore 3, and 0.13 on my v core 4
You can actually test this easily.
If you are willing to bend your X in the middle by pullying by your hand
Upwards
Do that, redo your Z, then Z tilt and then redo bed mesh.
Sure, the problem is not the x-gantry bowing. It would be perfectly understandable to have the bow, if it was consistent across the y, i.e. if it bowed the same at the front as what it does in the back.
But now I do feel silly..
Again due to the nature of the Z tilt
You will have a slope
If you X is bent.
As when it goes to do Z1
Since its going down more
Because of the X, it will actually lower your whole bed in the back
Which means you get a bed that not only goes down, but it goes slopoed on the Y
Again EASY test.
Bend it upwards
I do not quite understand how the Z1 would have an effect on how the x-rail bows in fron vs in the back
ANd redo the whole thing
Because it calculates your bed mesh with 3 points
And since the X is bent
Downards
In the middle
Z1 is tested in the middle
It will lower your Z1 more than it needs to, as in, not perpedicular towards z0 and z2
And you'll get a sloped and curved bed.
Yes, the tilt is calculated at three points, and tuned so that the three points are level. However, it does not affect how the bed or x-gantry bows in front vs in the back.
After the tilt adjustment, during the bed mesh measurements, there is no compensation happening during the measurement. The results are done one a static bed.
Therefore, no amount of front-to-back tilt (well, within limits, a 89 degree tilt would have an effect 🙂 will affect how the apparent bowing differs betwen front and back
But as said, I feel silly now, since I - for whatever reason - assumed that most of the error would be caused by the frame. Now that I measured the bed with a calibrated straight edge, it seems that dips are there because the bed actually bends that way.
Yes it does.
Again your X is bowed downards
In the middle only
Of course
So when it does Z1 the bed goes more than that it would go
And then you get again, sloped and inclied on the sides.
Easy test if you don't believe me
Just pully the X in the middle by hand
With some force
And redo the whole thing
I do understand that a bowed X-rail will cause an apparent bend on the mesh.
Well you can't really even go about fixing left and right back if you do nto fix your X gantry proper, so again your are back at square one.
Sure, I understand that the X-gantry would need to straightened, but that is another, separate issue. If this was only caused by a bowed X-rail, the bow/bump would be consistent across the y range.
No.
Again
Please
For your own sanity.
Pull your X gantry Upwards
And let me know
The result.
YOu'll see.
Its a simple test
THat will prove you wrong
Not because you are wrong in reading it but because its upside down on how it works.
You think it should work like that but it doesn't in case of a 3 point system
Just because the Z1 has, has to collerate to the X going downards in the middle
Ok, I will do the test. Meanwhile, can you explain how the tilt (in the order of less than 1degree) would cause the uneven bend on the graph? There no math or theory that I can understand that would explain why it would behave like that. And certainly I would like to learn, as it seem I have missed something very fundamental.
Simple, we are dealing in very small numbers, so even that little tilt over a 500mm for instance will give you an very odd shaped bed, in the grand scheme of thing it is truly very small, but since we are printing in small layers it is big for a 3d printer.
You have to first understand the bed itself.
Red = Close to the nozzle, and Blue = Far from the nozzle (just invert the bed with the Z axis and that is your real bed based on its ACTUAL size, not the compensation)
Since your X Gantry is going DOWNWARDS in the middle (Red), your z till will activate sooner on the back, hence giving a apparent slope to the bed.
The bed itself is not bent, but rather the Z is compensating properly based on the X gantry. And lowering your whole back by x amount of the degree it activates earlier.
To fix this, if you are using a 2020 most likely, you test this by bending it UPWARDS by hand. This will straighten out the 2020, and when you redo your Z tilt, it will fix the Z1 as the X is now flat and perpedicular left and right, and hence now in the middle due to your fix.
To ellaborate more on the dip, it is atually going upwards, as again (blue) color.
THis is due to again the slope of the Z1, which the farther you go from your front where Z0 and Z1 are flat to each other, you will have that slope more and more pronunced.
Don't be afraid to use force, if you push it too far Upwards you can always push it down.
You can actually see this in 24/7 video
His whole toolhead was in the middle in the transport
And made that dip on the 2020
Can you even consider entertaining the possibility that your view of how the tilt work might be improved by adusting it just a little bit 😄
Ok, as you see, the bed is pretty good at the front. Still bad at the back.
Just do more
Pull it
Again you can easily push it really gently down
Once you flatten it out
You want this
Of course. But do understand that even if I make it absolutely flat at the fron, it will STILL be bent at the back
247printing
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It won't be, please hahah
Trust me
I've shown you where he pully the thing
Again please don't be afraid to pull it in the middle
AS soon as the x is flat your back will be as flat
Sure, it might work in some cases, but that does not mean it works in all. The causes are not always the same.
In your case, it is because you ahve that gradient
THat is equal to the X gantry bend.
Pull!
PULL
Dont forget to mesure Z again
Then Z tilt
Then bed mesh
It is now even below zero in the front. Still dips in the back.
You still got a bit on the left as you can see red, but what is your whole variance
Check these points
YOu still have a bit of bannaa left
Can you screen shot the whole thing rather than just the bed now?
No amount of x bending/straightening will make the mesh flat.
But just a moment, I'll get a screenshot
Yes it will flatten it more, again, if you have a bend on the X just imagine, your whole left and right will sag as more closer it goes to z1
Man
You have a golden bed.
0.115.
GOLD
GOOOOLD
Don't touch it
No, that simply is not possible. If there is a bend in the bed, it is there. It does not go away with anything.
THe rest of this is the actual bed.
Yes but you are not probing the bed only
Is my point
When you probe oyu are pobing
The distance between the X extrusion
ANd the bed
And the 3 points of the bed.
Your bed is as flat as the factory would let it
And if you want it flatter on these corners
Add kapton tape
You'll be sub 0.0x
I promise you I'll make a video in great detail explaining this.
With practical examples.
The issue is you are expecting a perfectly flat X gantry and the whole frame to collarate to the bed
Which is not possible
If you had a perfect probing machine then yes, you would be right.
That would be good. But do keep in mind that if the apparent bend is caused only by the x-rail, it MUST be consistent across the y range.
Again we are talking atm
WIth 0.1mm
Beds are in that range
Of error
YOu can fix even this ofc.
With putting kapton tape
Sure. My vc3 was tuned to 60um.
But your X dictates how your whole back is acting
If it goes upwards for instannce
Blue
No, that is where we differ in view.
You'll get a slope but upwards
I mean view is one hting me testing over 20 beds and plates is another
I took a whole year just f*icking with my beds 😄
I'm not saying your points don't make sense, they do.
But I'll make a visualization why that is the way it is.
Yes. But when making it, pls consider that I am also pretty certain about my point of view 😄
But thanks, I would not have dared to lift my x-rail so heavily. It is indeed a pretty good mesh now
And as I told, and as my Veritas straight edge revealed, the 0.1 dips are indeed in the bed, they are not caused by the frame
Yeah no worries man, again we differ in views, and SOME parts do relate to the actaul frame because lets be honest nothing is perfect.
So a lot of factors come into play but the gradient in thsi case tells us a lot.
I don't want to me mean or anything we can differ
But I just want to ellaborate why and hows
You are absolutetly correct in that everything has an effect, I was not being precise. In fact I can admit that I was wrong there 🙂 But I still stick to my guns with the x-rail-causing-consistent-bowing view 🙂
Good talks, thanks!
@VisualTech48 I admire your patience 😁
@riksarchen Someone has to do it 😄
i hope you do understand that the issue I had was really, truly in the bed itself. A bent gantry will of course make a flat bed appear bent. But if the bed has a true dip at the back, as mine has, no amount of x bend will get rid of that, withot distirbing the flatness in the front. A bowed gantry produces a consistent error along the y. The error does not change. (This of course assumes that the bow stays the same durin the y travel. If it changes, then of course all bets are off.)
The issue we were discussing was a situation where the front of the bed appears flat, and the back appears bent. Such a situation is not caused by a bent x-rail.
Bowing the gantry would help if the front had a similar bend as the back. And in such a situation the bowed gantry will make the corners look like they were dipping, because the bed tilting will not make the bed ”horizontal” , but will simply level the three points it measures.
I admit being wrong about saying that the bed is causing the deviation: the frame and gantry are also contributing to the error. It is not only the bed, even though it might be the majority. But the basic concept of what can and cannot be fixed by bending a gantry I still defend.
In my initial post I say; ”Or perhaps, why does the x-gantry seem to bow more at the back than what it bows in the front”. That change in bowing is not fixable by simply bowing the gantry. Bowing will affect the whole y range.
Fortunately, we were able to make a real-world experiment, which showed exactly what I explained: even though the front was fixed, the dips in the back stayed. So, in this case, we have empirical evidence to prove a point.
The bed is only supported in three locations, and they are all at the edges of the plate. A perfectly flat plate supported in this fashion would be high where the supports are, a bit low in the front middle, and lowest in the back corners exactly as your mesh shows.
It would be, that is true. But I have no idea how much gravity affects. It would be a simple thing to measure though, just replace the back support with a bar that moves the the support to the corners. Don’t know whether that kind of experiment has already bee done, but if not I’ll try to give it a shot.
I tested this by setting up the back lift so that it lifts from the dognose screws at the corners. The dip did not disappear, so it seems the dip is not caused by gravity.
the recommendation is a range of 0.1% or less so on a 400mm machine thats 0.4mm. When my 500mm machine is heat soaked the gantry is taco'ing (if that is a word) 1mm+ and klipper heightmap deals with it fine. Don't chase problems that are not there and just print and enjoy the printer 🙂
I have not read every post in this thread but have you tried adjusting the feet up in the two back corners? These printers are so big they sag under their own weight and if the surface they are sitting on is not perfectly flat that will telegraph into the heightmap a bit. You are chasing a few thickness of paper at this point but if you want to try to get it a little better give the back two feet a turn or two, lock the nut on them down to the frame so they dont shake and then do a z-tilt and rerun your heightmap
Dont adjust anything.
Your bed is tacoing because of heat.
Its normal
There is a trick to uncrew I think the X gantry, then screw it down when its hot I think.
You can try that.
I know mine is tacoing because of heat. I was talking about mazas's heightmap. Screwing it down hot can help but the challenge with the gantry espeically on the 500s is that it takes a while to heat up. If you take a height map and its not fully warmed up it will continue to bow while you print. If you are printing something small you can probably get the first layer down fine, you are trying to print something big or a bunch of parts covering the bed you are in trouble
Yeah but thee is no way around it anyhow. You WANT your printer to stablize, because not only does the X warm up, your whole printer warms up basicly.
Believe me I know. I have had a VC3.0 500 since 2021 and was one of the first VC4 500 customers as well. I have a Toro3D tube to replace it once I get my IDEX kit. That should make a major difference in warm-up time.
@chicken I still recommend not just running the print asap, but yes it should take some time off it.
again I am well aware the printer needs time to warm up. Just hoping to cut it from 45 mins to 5-15 mins on a 500mm machine with a 100c+ bed temp
Perhaps an invesment for a large printer into a chamber heater?
already have one installed in the printer. The chamber temp gets up to speed quick but it takes a long while to get stable
Yea, the thread is getting quite long :). I am happy with the variabilit of the bed. My initial question was more of academic in nature: it is easy to explain one corner dip/peak with the frame, but it is not readily obvious what would cause two corners to misbehave. But then it turned out that it is not the frame, but instaed the bed. Problem solved 🙂
Easy actually, because of z tilt.
In reality, because your bowed gantry in the middle
Goes down
THe z tilt triggers earlier, making the whole bed to have a slope, that goes from the front to the back
The rest can be the bed but since its the same in both corners its most likely the latter.
No
Sloped the more it goes to the back
Because the back z tilt, will trigger before in the middle it will tilt the bed backwards in order for the 3 points to be at the same level
The front in your diagram is not flat. It is bowed, because a bowed gantry will craete consistent bow throughout the bed.
Well that is basicly what I'm explaining it is because of the bow of the X gantry that you can get a slanted and dipping back 2 corners.
Even if its slightly bowed, you will get it just that tiny bit.
You can even see it here,
THe further it goes back the further it is.
Sure, that is very true. I thought you were talking about the problem I saw
And to highlight once more: z tilt does not explain why the back corners dip if the front is flat. And it does not explain why back bows more than the front.
@VisualTech48 followed your suggestions in this thread and got a bed mesh to under .12mm range when heated to 60 C on my 400mm vc4. Thanks! My question to you is how can we guarantee the x gantry to stay like this? I would assume it is expected that the x gantry will sag over time and we just yank on it when needed. Not to mention potential expansion when enclosed. I saw you mention something about screwing and unscrewing the x gantry when it is hot, but I don't think I fully understand.
be very careful about yanking on anything. These are precision machines and yanking is going to not be good for them. A warp is not a big deal as long as the printer is stable. Klipper can deal with 1mm+ heightmaps differences without a problem as long as the mesh is stable from when it is taken and to when it prints.
@plutonasa In the grand scheme, this is just expected behavior, what you are aiming for is a stable printer before you print. By that I mean that the temp of the whole printer needs to stabilize.
Evem if you heat the mesh or it sgas over time you can of course pull it or you can retighten your x rail on a specific temperature once your whole printer is heat soaked.
With the current setup the bimezalic is unavoidable, the stability is important.
Now with the IDEX the difference is that you do indeed want as flat as a bed mesh, you can so this is. A bit trickier.
I've perosnally gone with the ti tube for this but it is really up to you what route you wanna go. On a 500 the gantry is 725 mm if I'm not mistaken and it will sag the most as the distance is quite large.