How many points max for manual leveling assist?

mrehorstdmd · 9 Jul 2018, 18:22

I didn't see it anywhere in the docs- is there a maximum limit to the number of points you can probe for the manual leveling assist? I currently have 5 points, one near each corner, and the center of the bed, and was thinking of going to 9 points (probably overkill). The bed has 3 leveling screws ...

Phaedrux · 9 Jul 2018, 18:50

Wouldn't 3 points be ideal with your setup?

mrehorstdmd · 9 Jul 2018, 19:28

@phaedrux If the bed is perfectly flat, three points should be enough, but if it isn't, using more points will use least-squares fit to bring the less than ideal surface as close to level as possible.

If the bed is actually flat, using more that 3 points will just add to the time required for the process.

Phaedrux · 9 Jul 2018, 19:31

At that point why not just run a mesh compensation? Actually, have you run one yet? At the very least the provided height map is interesting to see.

mrehorstdmd · 9 Jul 2018, 19:37

@phaedrux I've been wondering if it is possible to do that without a sensor...

Phaedrux · 9 Jul 2018, 19:43

@mrehorstdmd oh right you're using just an endstop. You can use manual probing for some features but I'm not sure about mesh compensation.

How bout trying to use stall detection on the z axis as a probe? You could still use the end stop for regular homing and use a macro to switch to stall detection, run a compensation routine, and switch back again.

I've used it when my BLTouch got damaged and it does work, though it has its own peculiarities. Your z axis has a single motor so that's a good start. Does it also have a high steps per mm?

If you're interested I could share the macros I used. You'd need to tune the sensitivity for your setup of course.

mrehorstdmd · 9 Jul 2018, 20:13

@phaedrux With my printer's Z axis, stalling the motor will probably do some damage to the hot-end/carriage/bed surface.

Phaedrux · 9 Jul 2018, 20:15

@mrehorstdmd right, the worm gear. Even with reduced motor current though?

dc42 · 10 Jul 2018, 07:07

@mrehorstdmd said in How many points max for manual leveling assist?:

@phaedrux If the bed is perfectly flat, three points should be enough, but if it isn't, using more points will use least-squares fit to bring the less than ideal surface as close to level as possible.

If the bed is actually flat, using more that 3 points will just add to the time required for the process.

That's all correct. The maximum number of probe points for this and all other least squares probing operations is 32.

mrehorstdmd · 10 Jul 2018, 11:55

@dc42 Great! Thanks!

mrehorstdmd · 10 Jul 2018, 11:57

@phaedrux said in How many points max for manual leveling assist?:

@mrehorstdmd right, the worm gear. Even with reduced motor current though?

I'd rather not find out the hard way.

wilriker · 7 Oct 2018, 14:20

@mrehorstdmd said in How many points max for manual leveling assist?:

@phaedrux I've been wondering if it is possible to do that without a sensor...

About Mesh Bed Compensation without a sensor: that is perfectly doable. You need to set your Z Probe type to 0 (M558 P0) and running a G29 afterwards will provide you with the same dialog as running G32 for manual leveling assist - which btw. I also ran with 9 points although only having 3 screws.

Meanwhile I dropped all of that because interestingly just leveling the bed at the screws gives me the best first-layer-adhesion I ever had. I have a small macro that will move the head to each screw, I'll adjust the screw old-school-style with a piece of paper. It will then do a second round just for fine tuning.
Before I was also running Manual Mesh Bed Leveling which showed deviations of up to 0.25mm between highest and lowest point but as I said dropping all of this led to best print adhesion for me.

EDIT: Just saw in your blog post about manual bed leveling that you already have the correct M558 command in your config.g.

One question I do have now though and maybe you can answer it: you have your leveling screws with Ref, Pitch and Roll assigned in a way I can follow. But on my printer I have the more traditional positions at the two corners and in the middle of the opposite edge. How would I assign Ref, Pitch and Roll in this case? Currently I have the one at the middle of an edge as Ref and the other two are... adjusters. Would there be a better assignment of roles for these screws?

mrehorstdmd · 10 Jul 2018, 15:21

@wilriker There are two screws along one axis in your machine- I would use one of those for the reference and the other for the pitch adjustment in that axis, then the third screw becomes the roll adjuster. The reason for doing it that way is because the roll adjuster has no effect on the pitch.

If you use the third screw (the one at the middle of the opposite side on your printer) as the reference and adjust the other two, every time you adjust one of those screws you tilt the bed in both axes. That makes it a little harder to level the bed manually, but It works either way, and with the assistant in RRF it's easy to make the adjustments regardless of which screw you choose to call the reference.

I'll probably try the mesh compensation just to see how it works. I haven't really had any problems with first layers sticking since I went to tooling plate, PEI, and 3 point leveling (always manual) a few years ago.