Auto_Bed_Leveling: Enhanced G29 command

[DarkAlchemist]

Nothing changed so I am baffled. same filament same everything only a different day. :/

Well, I don't want to have to keep finding the difference, if there is any, every single time I print. There has to be a way the machine can find that out for me but I am uncertain how. I was going to use some aluminum foil and a DMM so when the nozzle just touches the surface it would register but I found that will not work because the nozzle has insulating plastic all over it from the previous print jobs, lol. Besides we are talking about .02mm difference so I would need to move Z by .01mm to find if it has changed. I am just certain this can be done somehow without human intervention (I love automation).

As far as the M851 I still don't get what it exactly does so I can't really comment about it either way.

[Roxy]

Have you done the M48 Z-Probe Repeatability test? If that number is good, then the Z-Probe isnt the problem. But if that number is questionable, you will be fighting this until you get the slop out of it.

The M851 just lets you set the Z-PROBE_OFFSET from the keyboard, and you can save it if you like it with an M500 command. That way, you aren't going through the cycle of editing Configuration.h, compiling, loading the firmware for each number you try.

[DarkAlchemist]

Lastly, there is an E parameter. This Engages and Retracts the Z-Probe for each sample. It is a good way to see if your Z-Probe mechanism is adding any instability to your system. To check this, you could do a G28 and then a M48 n 15 x 50 y 50 followed by a M48 n 15 x 50 y 50 e command. At the end of each M48 command you will be told the standard deviation for the sampled points. If the M48 command with the e parameter has a higher standard deviation it is likely to indicate you have some inconsistencies in where the Z-Probe is being positioned between engagements.

OK... Now for the good stuff. Here is a cut & paste of my printer getting two M48 commands telling it to measure things at the center of the bed. One is with the Z-Probe down the entire time and the other is with the Z-Probe engaging and retracting.

Connecting...
Printer is now online.
>>>G28
SENDING:G28
>>>M48 x 100 y 100
SENDING:M48 x 100 y 100
M48 Z-Probe Repeatability test. Version 1.50
Mean: 4.162425
Standard Deviation: 0.009255
echo:endstops hit: Z:4.17
>>>M48 x 100 y 100 e
SENDING:M48 x 100 y 100 e
M48 Z-Probe Repeatability test. Version 1.50
Mean: 4.166162
Standard Deviation: 0.015431
echo:endstops hit: Z:4.16

I have very limited data to work with. I only know that my printer is doing well with the Auto_Bed_Leveling. With more people contributing their results to this thread we will probably be able to determine how much repeatability is necessary to get good results. My G29 command is modified so the Z-Probe stays engaged the entire time. Most of you will not have that feature so you probably should be paying more attention to the second standard deviation with the e parameter specified. Right now, my standard deviation is 1/30 of my typical layer height (because I'm comparing myself to the first result). It is possible the rational I'm using to choose the number I'm comparing against is flawed. I'm most certainly open to criticism and to being corrected!

I have never used that command and after re-reading the quoted part would you be so kind as to tell me what to do and I will do it then report back my findings.

edit: I did exactly what you did and here is mine

>>> g28
SENDING:G28
>>> m48 x 100 y 100
SENDING:M48 X 100 Y 100
M48 Z-Probe Repeatability test. Version 1.85
>>> m48 x 100 y 100 e
SENDING:M48 X 100 Y 100 E
Mean: -2.023075
Standard Deviation: 0.001230
echo:endstops hit: Z:-2.03
M48 Z-Probe Repeatability test. Version 1.85
Mean: -2.017900
Standard Deviation: 0.011545
echo:endstops hit: Z:-2.05

[Roxy]

The first number without the probe engaging and retracting is pretty good. That is telling you that if you make the same measurement you should usually expect to get a number within .001 of the 'correct' number. (That is a way over simplified description of Standard Deviation... But it serves our purpose here.)

The second number isn't horrible, but it isn't great. It is saying with the probe engaging and retracting and then measuring the same point, you will usually get a number that is 'about' .011545 accurate to the real number. If you had to move your nozzle .02mm, this could explain half of it. I don't think this happened... But if the first measurements when you set your nozzle height were off by .01mm in the wrong direction and then lately they have been off .01mm in the other direction, that would account for the full .02mm of adustment you had to do.

Can you show us some pictures of your Z-Probe and how it engages? There may be simple ways to change something and reprint it and make things better. I'm not saying this is something you should do. But take a look at the Z-Probe and the box for the servo embedded in the Extruder body.

http://3dprintboard.com/showthread.p...nsive+extruder

What I did was add a bump on my Z-Probe so it could only rotate so far and then it would hit a stop on the extruder body. That made it so there was no positioning error from the servo rotation. There are probably things like that which can be done to tighten up your numbers.

And one more thing... It might be good to run another M48 but do this: M48 V X 100 Y 100 L 5 and maybe M48 V X 100 Y 100 L 5 E

This will help see how much slop gets added to the measurement because of X & Y movement. Hopefully, you get very similar numbers to what you got without the L 5 parameter.

[DarkAlchemist]

Both of my numbers are of a tighter resolution than the ones your have yet I had this issue.

edit: Well, that was an interesting command, LOL, but here are the results:

>>> g28
SENDING:G28
>>> m48 x 100 y 100 L 5
SENDING:M48 X 100 Y 100 L 5
M48 Z-Probe Repeatability test. Version 1.85
Mean: -2.007175
Standard Deviation: 0.002121
echo:endstops hit: Z:-2.01
>>> m48 x 100 y 100 L 5 E
SENDING:M48 X 100 Y 100 L 5 E
M48 Z-Probe Repeatability test. Version 1.85
Mean: -2.025275
Standard Deviation: 0.013845
echo:endstops hit: Z:-2.03

[Roxy]

Both of my numbers are of a tighter resolution than the ones your have yet I had this issue.

edit: Well, that was an interesting command, LOL, but here are the results:

Well... Just to be clear... I'm not saying the Z-Probe error is your problem. What I am saying is any error there gets added to any other error in the system. So, if there is anything easy that can be done to tighten up those numbers, it should help the final result by that much.

One thing is clear... Your positioning error when you engage the Z-Probe is measurable. And it is in the range of .01 mm. Getting that tighter is going to help.

[DarkAlchemist]

Well... Just to be clear... I'm not saying the Z-Probe error is your problem. What I am saying is any error there gets added to any other error in the system. So, if there is anything easy that can be done to tighten up those numbers, it should help the final result by that much.

One thing is clear... Your positioning error when you engage the Z-Probe is measurable. And it is in the range of .01 mm. Getting that tighter is going to help.

yep, that swinging of the z-probe up and down is an issue but I am not entirely sure why. I mean if it engages the switch on its side or head on I can't see that as being .01mm of a difference but I guess it could. This is why I have always hated servos.

btw, I was thinking that I could move the arm until it can't move anymore then remove it and put the wiper there. So, fully extended it can't go back any farther unless you broke it. Would that help?

edit: just tried and it just doesn't go to a precise point so I need to make a physical block for it.

edit #2: I was thinking about this and I had the arm swing down via 85. Well, and odd number is not good so I switched it to 84 and got this -

>>> g28
SENDING:G28
>>> m48 x 100 y 100 e
SENDING:M48 X 100 Y 100 E
M48 Z-Probe Repeatability test. Version 1.85
Mean: -2.019575
Standard Deviation: 0.008766
echo:endstops hit: Z:-2.01
>>> g28
SENDING:G28
>>> m48 x 100 y 100 e
SENDING:M48 X 100 Y 100 E
M48 Z-Probe Repeatability test. Version 1.85
Mean: -2.009050
Standard Deviation: 0.007429
echo:endstops hit: Z:-2.01

[Roxy]

So that tweak helped! What I did on mine was have that bump hit the main extruder block so the probe can't rotate any more. And then I positioned the switch such that when the lever is getting pressed, it tries to rotate the probe a little bit into the stop so it stays tight against the stop for all of the points.

[DarkAlchemist]

I redesigned my servo mount to have a physical stop that is not going to budge. I made it 17.5mm from the far side so I can file it down as I measure 16.5mm. That will put 84 slammed up against it.

[Roxy]

I redesigned my servo mount to have a physical stop that is not going to budge. I made it 17.5mm from the far side so I can file it down as I measure 16.5mm. That will put 84 slammed up against it.

OK... But be aware of one more thing... The servo only stays energized for a short period of time in most setups. And I have seen some vibration when the servo is told to go past the end point. I tell mine to go just barely past the stop. It can't get there. And then I count on the fact the switch lever provides some torque during the probe to keep it pressed against the stop. Most likely, you will have to try a few things to get it perfect.