Gcode to read Z-probe offset ?

[exxos]

IS there anyway to read the Z-probe sensor values directly in Gcode ?

I think my bed expands as it's left on or something. When I print I have to use a 0.5mm offset, but this gets smaller and smaller as time goes on. Like the bed is expanding or something is shifting. So being able to read the sensor values would help figure it out.

[Badwolf]

IS there anyway to read the Z-probe sensor values directly in Gcode ?

I think my bed expands as it's left on or something. When I print I have to use a 0.5mm offset, but this gets smaller and smaller as time goes on. Like the bed is expanding or something is shifting. So being able to read the sensor values would help figure it out.

In Marlin I think it's M851 with no parameters.

BW

EDIT: oh, sorry, the sensor readings themselves? I doubt it. They're normally either 1 or 0 anyway.

[exxos]

EDIT: oh, sorry, the sensor readings themselves? I doubt it. They're normally either 1 or 0 anyway.

Yeah, mine's the magnetic sort, so kinda assume there would be a value there. But even 1 or 0 would be better than nothing. But I can't find anything.

I run this each time

Code: Select all

G0 Z-2.00; //move head down as homing moves up 2mm
G0 Z0.25; // start location 
G92 Z0; //set our new home

But I have to start with 0.50 offset and reduce it as the hours go on. I think it could be one of those things where my guy tried this morning, just heating the bed up to 60c and just leaving it for an hour before starting to print. Things seemed to be a lot more stable in doing that. I am not really convinced that magnetic bed is helping matters either.

[Badwolf]

Yeah, mines the magnetic sort, so kinda assume there would be a value there. But even 1 or 0 would be better than nothing. But I can't find anything.

I think it just acts like a remote end stop. On or off by way of a comparitor.

I run this each time

Code: Select all

G0 Z-2.00; //move head down as homing moves up 2mm
G0 Z0.25; // start location 
G92 Z0; //set our new home

But I have to start with 0.50 offset and reduce it as the hours go on. I think it could be one of those things where my guy tried this morning, just heating the bed up to 60c and just leaving it for an hour before starting to print. Things seemed to be a lot more stable in doing that. I am not really convinced that magnetic bed is helping matters either.

That's different to how mine works.

With mine you set probe offset with M851 then, at the start of each print you issue G28 to home, then G29 to do a mesh bed levelling pass. The G29 is optional but allows for a wonky bed (like mine).

At Z=0 the nozzle tip should then be printer paper thickness off the surface.

Now, of course, over time things will heat up. One of those things might be the probe holder, which means you height may vary by fractions of a millimetre. Not sure what you can really do about that other than buy one of the printers that just drives the nozzle into the bed and detects that via current draw. In all other cases there'll be a probe/nozzle lateral offset which will be prone to heat deformation.

BW

[rubber_jonnie]

EDIT: oh, sorry, the sensor readings themselves? I doubt it. They're normally either 1 or 0 anyway.

Yeah, mine's the magnetic sort, so kinda assume there would be a value there. But even 1 or 0 would be better than nothing. But I can't find anything.

I run this each time

Code: Select all

G0 Z-2.00; //move head down as homing moves up 2mm
G0 Z0.25; // start location 
G92 Z0; //set our new home

But I have to start with 0.50 offset and reduce it as the hours go on. I think it could be one of those things where my guy tried this morning, just heating the bed up to 60c and just leaving it for an hour before starting to print. Things seemed to be a lot more stable in doing that. I am not really convinced that magnetic bed is helping matters either.

All I can think of is that there is some sort of sensor drift because once at temp I wouldn't imagine things change, unless something else is causing the temp to change during printing.

[exxos]

@Badwolf There are offsets for the ABL. but the some reason it totally freaks out and actually makes things worse :roll: Lastly when I tried it seemed to think the bed was like 1cm higher one side. The Z-motor was going like nuts and the bed is like 99% level anyway. But even when it behaves it just seems to make matters worse which is why I just do manual adjustments.

@rubber_jonnie It's difficult to know why it does it. Maybe their head block and the bed itself expands marginally all the bed itself warps over time.

It is also possible the Z axis isn't great either. Still has those stupid wheels running up and down the thing. I have got a better linear rail for the Z but not had time to mess about with it all yet.

[rubber_jonnie]

@rubber_jonnie It's difficult to know why it does it. Maybe their head block and the bed itself expands marginally all the bed itself warps over time.

It is also possible the Z axis isn't great either. Still has those stupid wheels running up and down the thing. I have got a better linear rail for the Z but not had time to mess about with it all yet.

The bed axis really shouldn't change at all, is something loose and allowing it to float?

[exxos]

The bed axis really shouldn't change at all, is something loose and allowing it to float?

Don't think so. Will give ABL another go after the current print.

Though I get confused with Z-offset with the probe. As if I set a higher offset, does that then mean the probe has to go lower to the bed before it triggers as the offset is higher :stars: It's hard to figure out as things seem to change with where the printer thinks home is.

[rubber_jonnie]

The bed axis really shouldn't change at all, is something loose and allowing it to float?

Don't think so. Will give ABL another go after the current print.

Though I get confused with Z-offset with the probe. As if I set a higher offset, does that then mean the probe has to go lower to the bed before it triggers as the offset is higher :stars: It's hard to figure out as things seem to change with where the printer thinks home is.

Does your bed have adjustment at the corners? Mine does and I use a block of plastic of a known size to adjust the corners to be all the same, double check by measuring and then do ABL.

In fact I usually do ABL before every print since it's a crappy plastic bodied printer and it does drift. Once in a while I level the bed manually, adjust the nozzle height and run ABL again.

[exxos]

Does your bed have adjustment at the corners? Mine does and I use a block of plastic of a known size to adjust the corners to be all the same, double check by measuring and then do ABL.

Yep. I just homed and did the gaps with paper. I think on my flashforge it was better how I had it as the Z-probe had a LED on it. So at least I could get it all level manually easier than with paper.

In fact I usually do ABL before every print since it's a crappy plastic bodied printer and it does drift. Once in a while I level the bed manually, adjust the nozzle height and run ABL again.

Makes sense. Though with ABL it seems to drift out a lot worse.

Anyway I have taken out my adjustment code and just ran ABL. I also reset all the offsets in the firmware on the printer. Will print now and see what happens. Likely have to adjust the Z-offset and re-calibrate anyway.

EDIT

So far it seems to have started the first layer fine now :pullhair: I guess the thing would be to try it in the morning when it has all cooled down. Then run ABL and see if it still behaves.