G80/G81 Results
Does anyone have a confirmed explanation or definition of the results generated by the G81 command?
I'm running under the assumption it is a 7x7 interpolated and extrapolated array based on the 3x3 pinda based measurements. But which numbers represent which points is at best guesswork. I change left front .5 mm and the plane changes almost a full mm. And not where I'd expect to see a change.
My concern is changing a point elevation has dramatically 'wrong' changes in the answer. Here's a sample output and a 3x3 of actual measurements made with feeler gauges.
-0.148 -0.031 0.065 0.143 0.200 0.239 0.258 in an unspecified value and order
-0.125 -0.005 0.092 0.166 0.217 0.245 0.250
-0.092 0.027 0.122 0.193 0.239 0.262 0.260
-0.047 0.066 0.155 0.223 0.267 0.289 0.288
0.010 0.111 0.193 0.256 0.300 0.326 0.333
0.078 0.162 0.233 0.293 0.339 0.373 0.395
0.157 0.219 0.278 0.333 0.384 0.431 0.475
Though there is a correlation to my measurements:
-- in thousandths - looking down at table
Right Mid Left
0.042 0.030 0.024 <--- table farthest forward on rails
0.034 0.025 0.018 <--- table mid position on rails
0.026 0.020 0.012 <--- table farthest back on rails
Same data - referenced to highest spot to show deltas:
-0.030 -0.018 -0.012
-0.022 -0.013 -0.006
-0.014 -0.008 0.000
0.030" max delta, whereas the G81 result implies a 0.024" max delta (0.623mm)
Anyway -- knowing whet the numbers from G81 actually mean would be helpful.
Re: G80/G81 Results
This has been discussed in several other posts, but if you use OctoPrint with Prusa Mesh Leveling plugin, the display will be correct.
The values you receive from the G80 / G81 are as shown in the table below:
Left rear ----------------------Center rear---------------------Right rear
0.10750 xxxxxxx xxxxxxx 0.11333 xxxxxxx xxxxxxx 0.08000
xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx
xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx
0.14000 xxxxxxx xxxxxxx 0.12917 xxxxxxx xxxxxxx 0.06667
xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx
xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx xxxxxxx
0.13083 xxxxxxx xxxxxxx 0.12667 xxxxxxx xxxxxxx 0.08833
Left front-------------------- Center front--------------------Right front
Bear MK3 with Bondtech extruder
Re: G80/G81 Results
Some of us don't use Octoprint... why would we when we are dealing with a Prusa issue that provides tools to grab the data in question?
Thanks ... but this still doesn't explain the other values, Nor why when changing one location 0.5 mm the plot reflects a change somewhere else. Try raising the right front rail mount a bit and watching the carnage. If the entire right side is low by 0.4 mm, then raising the right rail by some factor* should correct it; but it doesn't seem to work that way. In some cases it gets worse in the direction you are correcting for.
By the way - sure the rails are reverse functions - but they should work to correct 'large' differences and twist. And fixing twist in the rails will help bearing life. Something in the way the numbers are reported fights using the data this way. Maybe it's an Excel thing, but so far attempts I've made to remove apparent twist have failing well into the miserable category. Though I have learned the power supply mount is warping the frame causing a front back deviation.
It would be nice to have threaded adjusters at the ends of the rails and software to report rail flatness based off pinda data. A future project for sure.
Re: G80/G81 Results
You do not need to use OctoPrint, you can use Excel or any other tool to display the bed graphically. But you must be aware that the G80 / G81 gauge does not come out the order that you think. The other values in the matrix are as you mention, interpolated
If you do not move the measurement values to a correct location, you may raise or lower the bed in the wrong place, believing you were doing the right thing.
Then the printer is so sensitive that if you loosen some screws in the bed and then tighten them again you will get a different measurement result than before.
Bear MK3 with Bondtech extruder
Re: G80/G81 Results
I change left front .5 mm and the plane changes almost a full mm.
Where did you get the information that 0.5 means 0.5 mm? I didn't see any mention of units. Maybe it's motor steps or something like that?
Re: G80/G81 Results
-0.148 -0.031 0.065 0.143 0.200 0.239 0.258
-0.125 -0.005 0.092 0.166 0.217 0.245 0.250
-0.092 0.027 0.122 0.193 0.239 0.262 0.260
-0.047 0.066 0.155 0.223 0.267 0.289 0.288
0.010 0.111 0.193 0.256 0.300 0.326 0.333
0.078 0.162 0.233 0.293 0.339 0.373 0.395
0.157 0.219 0.278 0.333 0.384 0.431 0.475
The numerical values presented after the commands G80 / G81 are given in mm, plus and minus from an imaginary 0 value.
If we start from the center point value (0.223), then the four corners should be adjusted as follows:
0.223 - (-0.148) = +0.371 mm
0.223 - (+0.258) = -0.035 mm
0.223 - (+0.157) = +0.066 mm
0.223 - (+0.475) = -0.252 mm
If you cannot lower a point, you will instead have to raise the center point so that it becomes highest.
Then it will be easier to adjust up the other 8 points.
Bear MK3 with Bondtech extruder
Re: G80/G81 Results
The numerical values presented after the commands G80 / G81 are given in mm
Where does that information on the mm come from? Does Prusa offer some official technical information on this?
I noticed something odd: I installed Bed visualizer and Prusa Mesh Leveling and they give me different results. One seems to be a mirrored image of the other:
(Update: I just figured out that you have to check the option "flip Y-axis" in bed visualizer. Then the images correspond)
Re: G80/G81 Results
Where does that information on the mm come from? Does Prusa offer some official technical information on this?
In chapter 6.3.7 "Mesh bed leveling" it is stated that height adjustment is made in mm.
However, it is not clear-text that "Mesh bed leveling" is the same as the commands G80 / G81. If you know these commands then you are expected to know the connection with "Mesh bed leveling".
Also in chapter 6.3.9 "First layer calibration" it is stated that the numerical values in the display indicate the Z level in mm.
So now you can start adjusting the bed to make it level as a mirror surface 😀
Bear MK3 with Bondtech extruder