Anyone else interested in z-probe readout?

[gremlin529]

Not even sure what to call this, but I'm still having some issues with the bed on my cbeam-xl not being quite level to the X axis, everything seems square when I measure it and use machinist squares, but when I do a cut that's supposed to go through it does on one side and misses by a little bit on the other.

So I was thinking of trying to work out how to modify the Z probe code to just do a touch down on the probe and return back to me how far from zero it is currently, so then I could zero it on one side and take several measurements along the bed to see if it's a trend or a warp issue or what. 3d printers do this before every print and actually have code in them to compensate for anything in the bed, I think that'd be harder with a CNC but it might at least help figure out how far out the bed is.

[SirGeekALot]

I could see this being helpful. Perhaps a way to put a touch plate on various locations and have it just spit out the z position?

[gremlin529]

I actually considered some way of just putting a piece of metal down and letting it do several points acrocc the entire bed, I've done a bit of research and I have a pretty good idea on how I might make this work. Let me see what I can do.

[housspin]

I added a metal extruder bar across it, and now it’s much more stable with more accurate results.

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On Mon, Nov 3, 2025 at 6:43 PM gremlin529 ***@***.***> wrote: *gremlin529* left a comment (OpenBuilds/OpenBuilds-CONTROL#403) <#403 (comment)> I actually considered some way of just putting a piece of metal down and letting it do several points acrocc the entire bed, I've done a bit of research and I have a pretty good idea on how I might make this work. Let me see what I can do. — Reply to this email directly, view it on GitHub <#403 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ADGHEJ43EUEOVM2KKLTPZ6L327K7HAVCNFSM6AAAAACK5I2RVCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTIOBTGA2DAOJUGE> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[swarfer]

I have had good success using a microswitch like the ones used for limits as a probe.
I glued it to a magnet and just stick it to the collet when i need it (usually for scanning PCB surface before cutting).
I sanded a 6mm plastic ball in half then glued it to the switch arm.
Glued the switch to a round magnet such that the ball is in the center of the magnet, makes it easier to align on the spindle.
Now I can stick the magnet to the collet (take the bit out) and center it by feel.
I always lead the wires off to the right, not critical but it makes the reading more consistant.
I use bCNC which has a built in surface scanning function and applies the scan to the Gcode.

however, the most common way of 'fixing' a nonflat bed is to use the surfacing wizard in OpenBuildsCONTROL to cut the spoilboard 'flat'. (it will only be flat if the frame is flat (aligned is the correct term) of course). Use the largest flat end bit you have, and only cut as much as you need, maybe 0.020" is enough.

[gremlin529]

That's brilliant, I'll have to look at bCNC and see how that maps, I love the idea that it can get out imperfections. I have an openbuilds CBeam XL and have taken it apart a few times, to try and square everything perfectly, and with digital levels and machinist squares I still can't get the damn thing 100% parallel on the X axis, so I'm trying to work out other ways. I'm going to run a spoil board pass again, but I'm trying to work out how much I can take off as I use dovetail microjig style slots in the spoilboard for clamping. And with engraving a surface I just wonder if it would work better to map it.

[SirGeekALot]

I agree with swarfer (good name BTW 😊) that the flattening wizard is the right way to go first. That being said, if your frame is not squared and fully trammed, and your spindle is not fully perpendicular to both X and Y, and you use a large diameter flattening bit, you will see lines show up, especially when you use a small stepover percentage. This exposed my spindle's not fully perpendicular mount problem. Increasing my stepover helped hide it. But I really need to figure out a way to fix it, but I haven't yet. I have a large format OpenBuilds OX CNC router with the quiet cut spindle. Not super fancy but it works for my non-critical precision needs...for now.

[swarfer]

That's brilliant, I'll have to look at bCNC and see how that maps, I love the idea that it can get out imperfections. I have an openbuilds CBeam XL and have taken it apart a few times, to try and square everything perfectly, and with digital levels and machinist squares I still can't get the damn thing 100% parallel on the X axis, so I'm trying to work out other ways. I'm going to run a spoil board pass again, but I'm trying to work out how much I can take off as I use dovetail microjig style slots in the spoilboard for clamping. And with engraving a surface I just wonder if it would work better to map it.

For engraving it is critical to map the surface, much like for PCB cutting. Any surface/cut depth variation is immediately visible in the width of the cut with a V bit. DO do some experimenting with scan density and figure out what spacing is really needed as too high a density takes far too long, but too low a density will not track the surface well enough.

You can also attach an extra spoilboard using the masking tape and CA glue method then flatten that to high precision as needed.
I often do this with just a 6mm sheet of EPS insulation foam, cutting into it can be done at any speed/feed and does not affect the final product. (though I do find that cutting through the tape causes glue to stick to the bit which can have side effects)

[gremlin529]

Are you running bCNC with a black box controller? I was trying that out today and I can't for the life of me get it to do anything but alarm and jog the machine around I tried all sorts of settings and machinations

[swarfer]

Yes, there are some settings to change but I cannot recall exactly what righ tnow, I will check tonight when I get home (GMT+2 timezone)

[swarfer]

you do need to get the $10 value right, 511 is working for me.
other than that grblHAL defaults to Normally Closed limit switches so they may nee dto be inverted, same with probe.

What is the actual alarm message in the Terminal ? (top right of bCNC window)

[gremlin529]

@swarfer thanks I'll check on that, Sounds like these are things that would need to be changed if I Swap between the control software then, anything you figure out could be helpful, I'm messing about with gSender now too to see how that works

bCNC took quite a lot to install so I wondered if I'd messed something up. For instance everything insistend Python would just install the package for the GUI but it didn't in any version until I went to the app store and got it there, even then I think I had to do some other messing about to get it properly registered.

[Wicked-Creations]

@gremlin529 are you talking about Z height mapping or surface mapping (https://youtu.be/VY4cevyGYA4?si=i0PXsfB754mejPdI) ?

Which is basically probing the surface at multiple XY points to create a height map and then using that map to dynamically compensate the Z axis during motion so the tool maintains a constant cutting depth even if the surface isn’t perfectly flat.

I wanted to do the same for PCB milling for example probing the copper board first generating a Z height map and then modifying the effective Z values while the G code is executing so the engraving depth stays consistent across the entire PCB. As I am doing here > https://www.instagram.com/p/COa09CUpQ4k/?igsh=MWVuN3NzOXVmdnJqcA==

Have you already started on this?

[gremlin529]

Yeah that's what I'm talking about, but I was thinking of not just for circuit boards but also for slight variations in the bed or other material. I started into figuring out how it could work, then switched from using OpenBuilds to gSender and haven't really gotten back to thinking about it.

I did spend a bunch of time doing some macros to measure height at different places while I was working on making sure my Y Gantry was parallel to the bed,

[Wicked-Creations]

Ah but gSender does not have a feature to do surface mapping?

[gremlin529]

Sorry, should've been clearer no it does not, but it does allow some cool macro stuff, so I used that to map out my table and figured out how to get it more square which is where I was having an issue, someone mentioned some other software that does do the mappng, but I was unable to get it to work on the machine I was attempting on, I only gave it about an hour but couldn't reliably get it to talk to my CBeam XL.