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hoegge

Auto bed leveling is not accurate at all - most prints fail

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Just got an UM3E. Lot of experience with printing using CR-10 and Prusa i3 MK2s.

 

When I want to print ABS with the UM, the leveling is way off. The printer starts heating the print core, then it does it's leveling "magic" and THEN it heats the bed (to the 100 Celsius). When the print starts, the distance to the plate in the back is a bit lower than 0.2 mm first layer is set to and at the front the layer is about 0.0 mm and I have to turn the screws to get it to extrude.

 

A 0.2 mm calibration error is NOT ok at all. The error should be less than 0.05 mm and preferably around the +/- 0.015 mm error I achieve on my CR-10 to get good first layers.

 

Since everything on this printer is controlled by the printer, there is no good way to manually correct this, and it shouldn't be necessary. I would expect one of the things you pay a lot for in addition to the nice swappable print core solution is accurate and fool proof bed tramming - if this does not work, UM3 seems to be a waste of money.

 

When I calibrate a bed manually I always do it after heating both bed and nozzle - the UM heats the bed after calibration. Is that the big mistake, that ruins the bed leveling? The bed hangs attached only in one end and is a bended alu plate. Not unrealistic to think it could bend 0.2 mm when heated from 20 to 100 degrees.

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I do not experience this. I do set a manual every now and then to account for any drift in the leveling as it goes up and down and through heating/cooling cycles as well as plates being bumped around for whatever reason.

 

But, when active leveling, I do not have issues with it at all. All of my failed prints can be traced to mostly user error.

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Same as @kmanstudios, I never had that problem since I got my UM3E. I do manual leveling from time to time, and let the active leveling work it's magic with each print.

 

Did you check to make sure there isn't something in the big screw that could hinder the vertical movement of the plate? Did you also check if your plate is flat enough? It seems that quite a lot of glass plate are bent in a U shape, more or less heavily. I had to get a replacement for my first plate because it was way too bent.

 

The main problem I had at the start when leveling was due to a misunderstanding of the instructions: when it went to calibrating the z-offset for the second core, I would turn the screw instead of turning the front wheel. Baffled for a time before I understood my mistake (not native-english speaker). That might also explain your leveling problem.

 

 

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3 minutes ago, Brulti said:

Same as @kmanstudios, I never had that problem since I got my UM3E. I do manual leveling from time to time, and let the active leveling work it's magic with each print.

 

Did you check to make sure there isn't something in the big screw that could hinder the vertical movement of the plate? Did you also check if your plate is flat enough? It seems that quite a lot of glass plate are bent in a U shape, more or less heavily. I had to get a replacement for my first plate because it was way too bent.

 

The main problem I had at the start when leveling was due to a misunderstanding of the instructions: when it went to calibrating the z-offset for the second core, I would turn the screw instead of turning the front wheel. Baffled for a time before I understood my mistake (not native-english speaker). That might also explain your leveling problem.

 

 

It took me about a month to realize there was a screw in the back, underneath the buildplate. Found that out reading threads. I was always using the wheel in front and just ever so slightly nudging it to get it as close as I could. Sigh.......Such is the price of noobdom...LOL  ;p

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3 hours ago, Brulti said:

Same as @kmanstudios, I never had that problem since I got my UM3E. I do manual leveling from time to time, and let the active leveling work it's magic with each print.

 

Did you check to make sure there isn't something in the big screw that could hinder the vertical movement of the plate? Did you also check if your plate is flat enough? It seems that quite a lot of glass plate are bent in a U shape, more or less heavily. I had to get a replacement for my first plate because it was way too bent.

 

The main problem I had at the start when leveling was due to a misunderstanding of the instructions: when it went to calibrating the z-offset for the second core, I would turn the screw instead of turning the front wheel. Baffled for a time before I understood my mistake (not native-english speaker). That might also explain your leveling problem.

 

 

Well, for the second printcore, it actually says "Wheel" on the first position and screw for the next two. I assume you should use what the printer tells you?

I have turned the three screws up and down to full extend and then redone the manual leveling. Did not really help much but then I heated the bed before starting the print, and I suspect, that is where the issues is. A bed going from 25 degrees to 100 degrees, might change position since the aluminium holder, will. After that, calibration was much better. I think though the UM 3 I have behaves too weird, and I'll try to make a better description later, describing the problems I see with it.

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I second the occasional manual level. 

 

Automation is fabulous, but I have to remind myself, it all works on engineering assumptions, which don't yet account for everything in the real world.

 

As a fellow noob, I have found I have a remarkable skill for defeating engineering assumptions....

 

John

 

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13 hours ago, JohnInOttawa said:

I second the occasional manual level. 

 

Automation is fabulous, but I have to remind myself, it all works on engineering assumptions, which don't yet account for everything in the real world.

 

As a fellow noob, I have found I have a remarkable skill for defeating engineering assumptions....

 

John

 

Yes, if you let it, solid tech can be an evil succubus, lulling you into a false sense of complacency.

 

I am going to have to steal that line about defeating engineering assumptions. :) But, also remember that sometimes engineering and design assumptions do not take the variety of users needs and actions into account.

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You are most welcome ;-) .  As my dear departed mother once told me, there are some whose life serves as a fine example.  I, on the other hand, was destined to be a cautionary tale.....

 

I do, however, take some solace in watching the absolute carnage my bride wreaks on technology.  Not only does it keep me perpetually useful around the house, but it constantly opens new experiences for me.  For instance, before meeting her, I had never seen a computer quake in its boots and crash just to get it over with.

John

Edited by JohnInOttawa
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On 1/30/2018 at 2:32 PM, hoegge said:

Well, for the second printcore, it actually says "Wheel" on the first position and screw for the next two. I assume you should use what the printer tells you?

I have turned the three screws up and down to full extend and then redone the manual leveling. Did not really help much but then I heated the bed before starting the print, and I suspect, that is where the issues is. A bed going from 25 degrees to 100 degrees, might change position since the aluminium holder, will. After that, calibration was much better. I think though the UM 3 I have behaves too weird, and I'll try to make a better description later, describing the problems I see with it.

 

"Wheel" means you make the adjustment with the button on the front of the machine, so you're actually changing the height recognized/saved on the Z-motor itself, so it should ask you to use the wheel/button for the back center leveling location for both print cores. For the 2 front leveling positions, you use the thumbscrews on the bed itself to sort out the spring tension. For major adjustments on the printer, you can use the back thumbscrew also, but in general, the back thumbscrew shouldn't usually need to be touched most of the time.

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