Hints about auto-leveling and probing

[Mark81]

Often I have to engrave signage with very small depth (-0.1 mm) and quite large size (600x450 mm). The bed of my machine is fairly flat, but on such a long distances I have about 0.1-0.2 mm of difference.
Usually, we use a sacrificial stock so you can flat it down with a large tool. In my case I cannot do that because the material I have to engrave is larger than the working area of the CNC and just sits on the whole bed. So I cannot flat only the working area, because it would be lower than the outer sides.
I think this is a good scenario to use the auto-leveling plugin! I'm going to probe the bed, digitize and save the file to be loaded whenever I need to do this job. Because the bed doesn't change over the time I think this is a one-shot operation.

Are you agree with my thoughts?

I don't have a touch probe yet, and right now I cannot afford a commercial one. They are too much expensive at the moment for me.
I wonder: because I don't need an edge finder, but I need to probe the Z-axis only, do I really need the "three-ball" system? Would not be enough a simple switch (with a very good repeatability) placed into a tube with a concentric probe?

EDIT:

One more thought. Because I'm going to digitize the bed (Alu) perhaps it's enough to use a chuck and connect it through the bed itself. When it touches the bed it will short the connection and the software will read the input. Going down slowly enough should do the trick. What about this?

[dezsoe]

Many of us use the simple touch-and-contact style proging and it works really fine. The only thing you have to know that where is the bed and the the chuck connected. If you are not sure, you should use some isolation to connect the probe. What kind of motion controller and breakout board do you have?

[cncdrive]

Yes, that is the purpose of the autoleveler plugin.
No, I don't think that you need a 3D probe, you need a touch probe on the Z-axis to measure the table surface on different points.
I suggest you try to "dry-run" the autoleveler plugin to see how it works, so you will have more ideas about it.

[Mark81]

What kind of motion controller and breakout board do you have?

UC300ETH_5LPT and a custom breakout board made by the factory that built the CNC.

[dezsoe]

Is there any documentation about that breakout board? If not then you should ask the manufacturer.

[Mark81]

Yes, that is the purpose of the autoleveler plugin.
No, I don't think that you need a 3D probe, you need a touch probe on the Z-axis to measure the table surface on different points.
I suggest you try to "dry-run" the autoleveler plugin to see how it works, so you will have more ideas about it.

I'm trying right now the plugin. I read the related thread but still I'm not sure to understand it correctly.
It requires a gcode to start collecting data.

Instead, I just want to probe my whole area, given a start point (x, y) and distances. Then, I can put my stock anywhere on the bed at the software will already know how to compensate in that particular location.
I'm thinking to draw a "dummy" gcode with a rectangle of the whole area to fool it... but I'm not sure this is the right way!

[cncdrive]

What the autoleveler plugin does is that you load in a g-code file (toolpath) and then the autoleveler probes the surface area and then it modifies the g-code file, it compensates the Z heights in the file to fit the probed surface.

To just measure a surface, for that the way is to make a g-code with G31 probing codes or probing macro calls in e.g. a grid.
And in the beginning of the file you can run the M40 macro to start collecting probing data and at the end you can call M41 to save the probing data into the file setup in the digitize menu in the UCCNC.
So, you will have a csv point cloud file which you could use for whatever you want... I don't really understand though what and how exactly you want to do...or even if you need to do this or something else is what you looking for. Sorry, I just don't understand from your description.

[Mark81]

Thanks for your answer!
I'm sorry for my poor explanation. I'm trying to explain it better.

The autoleveler plugin requires this procedure:

1. load a g-code
2. probe the surface (according to the file)
3. modify the g-code to compensate Z-heights
4. run the job

I'm going to use the plugin to engrave signage. Because the bed of my machine doesn't change over the time, I was thinking of probe the whole working area (you told me how to) and save the digitized file.
Then when I need to engrave anything I would (ideally) use this procedure:

1. load the digitized file
2. load the g-code and zero working axis (so now the software knows where the job will run, and hence use only the points that fall inside that region)
3. modify the g-code to compensate Z-heights
4. run the job

Bottom line: I don't want (if possible) to probe the area every time I load a new g-code or every time I run the same g-code at different locations. I'm just trying to "know" my machine's bed and compensate any g-code I will ever load (if requested, of course).

Please, feel free to ask more details if I still explained it poorly!

[cncdrive]

I understand now, but what you want to do makes no sense in my opinion. (probably this is why I did not understand for first)
It does not really makes sense, because the purpose of probing the surface is that the workpiece sheet is usually isn't 100% flat, it can be a bit bent and can have thickness differences,
but what you want to do does not solves this problem, because the sheets can differ by piece.
The other thing is that your table (bed) or a spoil board on it can be and should be machined with the machine to make it constant height to your machine Z.
It does not mean it is flat, because if your machine axes (linear rails and body) are not straight and not flat then machining that spoil board will not make the board flat, but it will be constant height compared to your machine.
And probing can't help on a non precisely squared and flattened machine body, because the probing happens on the machine.
So, the simple solution for what you want to do is to machine a spoil board on the machine with the machine.

[Mark81]

Got it.
I'm used to flat my spoil board periodically.

This application is quite different I think. I don't want to insist, but it's just to better explain the application.
I need to engrave large signs, larger than the working area of my machine. Of course the milling operations are contained in the working area but the stock will sit on the whole bed, not only inside the working area.
When I do this I use a specific spoil board, called Gravogrip (https://www.gravostoreusa.com/eng/product/45696) that covers, as said, the whole bed.

So, I cannot "machine" the working area only, because this board will flex outside (I need to keep the unevenness < 0.1 mm).
I'm not sure about this:

And probing can't help on a non precisely squared and flattened machine body, because the probing happens on the machine.

Of course, but we're interested in the distance from the tip of the tool.
So the probing shows how much the spindle must come down to touch the material in that specific (x, y) location, no matter the actual Z height. Am I wrong?

Anyway, I understand what I've asked is not possible so I cannot even give it a try
I'm going to follow both ways (standard procedure, and machine a spoil board - even if smaller than the stock piece) and see what happens!