So I had an idea on making bed calibration simple.

[curious aardvark]

Since it was pointed out to me how to adjust z-level in simplify 3d: gcode tab and adjust z offset.
I've been thinking how to use that to avoid having to calibrate the print bed or to simplify the process when i actually need to do it.

I've got spirit level utility on my android tablet, had a play with that and it will let you set any situation as being 'flat'.

Ah ha !
Use spirit level to level bd and z-offset to adjust height, seems simple enough.

So i put the tablet on the guide rods of the printer and zeroed it.
then put that on the printbed and adjusted till it was the same as the rods.

Should have worked right ?
Nope. Was the most out of whack I've ever seen it.

So I recalibrated normally - this time remembering to heat the bed - yeah.

But even with the bed heated the two readings still don't tally.

It was a potentially good idea - but the bed is not aligned to the guide rods, which is why you need the levelling knobs :-)

Just thought I'd document this in case anyone else has the same idea, and remembers to heat the bed and uses abs and cooks their phone/tablet :-)

In fact heating up a phone or tablets lithium ion batteries to 110c, could well cause them to catch fire or explode - so don't do it !

[djprinter]

How in the he heck to do you "level" the bed without affecting the height?

Also do you really expect a phone app to be accurate enough? All level apps I've seen only show the 1st decimal point, you'd need 100 times more accuracy than that to level.

The angle of a bed tilted by 0.1mm (which is too much), would be less than 0.03 degrees

[curious aardvark]

well you can adjust the height in the software :-)

Yep, as you pointed out - it doesn't work :-)
Sometimes it's worth trying things. I have no idea how accurate the sensors in the tablet are, as it turns out they were fine, it's the arms holding the plate that aren't level :-)

[Roxy]

The angle of a bed tilted by 0.1mm (which is too much), would be less than 0.03 degrees

If you run Marlin, there are a number things going on. First, there is a UBL (Unified Bed Leveling) branch going that uses a High Resolution Mesh as the foundation. It has a built in Mesh Validation Tool (G26) that can be used to quickly edit the Mesh. I can tell you I've deliberately sought out the worst piece of glass I could find. I've got nearly 1 mm ups and downs across its face. I can get a perfect first layer every time.

It is a development branch right now because the code is changing fast. (Some people are best off using 'Stable' or 'Release' branches.) You can get it here: https://github.com/MarlinFirmware/Marlin/tree/devel-ubl

There is also a discussion about how to emulate the Prusa MK2 XYZ Calibration without extra hardware. That thread can be found here: https://github.com/MarlinFirmware/Marlin/issues/4904 It is possible that we we will add the GCode's into Marlin to automatically print the calibration pieces.