Any way to make constant-depth spherical cut?

No worries. I completely understand when life gets in the way of the fun stuff.

I have the educational version of SolidWorks for 2022-2023 or something like that, so I should be able to open up the file just fine.

I’d about swear I had a reply from you with your e-mail address, but I can’t find it now. ??? Am I making that up?

It’s in your inbox. I think the have to go to your inbox, but it defaults to “unread”, so you have to select either “new” or "latest.

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You don’t need to model the spherical nature of the workpiece to follow it. There are a few CNC driving programs that offer heightmapping/autoleveling capabilities to take a G-code program’s toolpath and offset it to follow a grid of Z-probed points.

I do it all the time for V-carving warped boards without the carve coming out wonky. I designed and built a custom touch-probe for making the process as painless as possible but you can just connect up your controller to the workpiece and your cutting tool and have your machine probe out a grid of points to offset your engraving toolpath.

Granted, I don’t know about the Shapeoko machines - I’m running an Arduino/GRBL rig, and all that’s needed is that I connect the tool to pin 6 and my workpiece to ground (IIRC) and then Candle makes it easy. That’s for when I’m cutting something that’s conductive, like metal. You’re basically just creating a circuit from the controller through the workpiece and the cutting tool back to itself, so it can detect when the tool is touching the workpiece.

The heightmapping functionality of these programs is typically used for milling out copper-clad PCBs, because they’re not perfectly flat, but you also don’t want to cut too deep - just cutting off that tiny thin layer of copper, so heightmapping is used to offset a PCB trace toolpath to conform to the actual PCB and minimize material removal.

I’m surprised nobody has even suggested this on here - everyone is thinking the only way is to actually model the spherical nature of your workpiece. Just use CNC probing!

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One tool which supports that is bCNC.

Wow - how cool! I had no notion this was an option - at least not at the DIY/hobbyist level. It’s surely the optimal solution for my project. I say that because I don’t have great faith in the accuracy of my SolidWorks model of the motorcycle side cover. I made the model using measurements I took using a pair of calipers and a combination square but had no real way of measuring the spherical radius of curvature. In fact, I’m not sure it actually is spherical. Man, as a newbie in the CNC world I find each new project opens up new rabbit holes, and I also find there aren’t enough hours in a day (or at least in a weekend) to explore them all to my satisfaction. I think I need to retire early. Anyway, can you suggest a probe for purchase? I would expect to have to fabricate my own mount for it, as you did. Or, come to think of it, it seems it would be best if it went right in the collet where the cutter bit would be later. I had a quick look at the videos, and will watch them in entirety tonight after work. Thanks very much for the suggestion. It would be a great capability to have - for this and many other projects.

Thanks, Will - I’ll go check it out.

Oh. Duh. Thanks. I’ll send the file this evening. I was messing with it last night and need to get it back in a less boogered-up state. One big change though is that after talking with the guy I’m doing this for (he rents a shop near mine) he told me he doesn’t want the whole Japanese character cut out - only the perimeter of the character, i.e. like an engraving. But it still needs to be a spherical cut, of course. Very interesting suggestion from radioteeth though, huh?

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I knew that bCNC did surface probing, but I learned about it when I was looking into cutting PC boards. I never considered it for this kind of application.

If the part is metal you can just directly probe it without a touch probe, just using the cutter itself as the probe. You’re just closing a circuit between the cutter and the workpiece itself. Just be sure it’s not going to leave a grid of marks across the surface :stuck_out_tongue:

As for acquiring a touch probe to do other materials with I have no idea what’s out there now but there were a bunch when I was looking ~5-6 years ago. When I designed and fabricated mine it was because none of the ones I could find to buy had a low enough profile. Their housing and probe length wouldn’t have left a lot of room on the Z-axis of my machine even if I chucked it all the way up into the spindle.

Just be sure not to confuse a tool zeroing probe with a touch-probe!

I’d like to hear (read) a bit more about this. I keep looking for a universal (not just metallic) probe but have the same issues. Too tall, odd sizes (or metric), cheap chinese junk…
After taking apart the Bitsetter several times to clean it out, I have to imagine a probe wouldn’t be rocket surgery, but tolerances would have to be pretty tight. Thinking about ways to use the same kind of proximity sensor & allow both vertical & horizontal movement without any slop.

[Nevermind] Found it… DIY Touch probe , Renishaw Tip - #22 by PhilG


Thanks all, for your input. I’m about to leave for a 4-day trip so I won’t be able to mess with this until next week, as much as I’d like to. But I’ll be thinking about it…

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Another option for probing uneven surfaces is Estlcam, though I haven’t actually used it, still looks promising.
And here’s an engraving example on a computer mouse.

Thanks for that tip and the links, MikeG. I just went and did some research on Estlcam. I agree it looks good. His trick using the aluminum tape to make the surface being probed conductive is simple but very clever. The thing is, there are two aspects of this I haven’t found a good explanation of:

  1. How does one connect the two wires in the closed-loop circuit to the Shapeoko? Connecting one to a grounded screw (which has continuity to the cutting bit) is of course straightforward, but the other one has to connect to the controller board somewhere - but where? In the video the Estlcam guy says he “just put some aluminum tape on the mouse and connected it to the probe input”. It’s not clear what his machine is. Does the Shapeoko controller board have a “probe input” pin/port?

  2. Once the above set-up is done, the surface has been probed, and the file containing the XYZ point cloud has been created then what? In his video, right after the probing process is done on the mouse, the Estlcam guy says, “The CNC program now has the same curvature as the mouse… so we can just start the program.” And then the cutting starts. There is no info on how the intended 2D cut is transposed into a 3D cut by melding the two sets of data. Maybe it’s straightforward once you become familiar with the software.

I just downloaded the free trial of the Estlcam software and hope to check it out this weekend.

Thanks again.

I meant to include these links for you and the others on this thread; MadHatter, Tod1d, radioteeth, and WillAdams. It looks like this probe is small enough to work with the tight Z-travel of the Shapeokos. And it’s made by a Czech company, which is generally a very good thing when it comes to machine tools, according to my veteran CNC friend.

While I like the Estlcam guy’s foil trick and can still see using it, it would also be nice to have this direct probing capability.

Not sure, but thinking that using the BitZero lead would do it. @WillAdams or @Julien probably has the answer, or knows where to get it.

Yes indeed, BitZero and/or BitSetter tend to like to be connected to the Probe input :slight_smile:
All Shapeoko controllers have (of course) a probe input, but where exactly this is accessible on the circuit board depends on the controller type and there are now several, but as far as I can tell they all have it written on the silkscreen (“P” or “Probe” or “BitZero”). Since this is an unsupported mod, triple-checking is advised to not ground the wrong signal, or blue smoke may appear :slight_smile:

Thanks for your input, Julien. I’ll have a look at the board in my Shapeoko (Pro XXL) when I’m back at my shop later this week. It sure seems like there’s got to be a reasonable solution to this. It seems like such a fantastic capability.

Julien, MikeG, and others -

I was doing some more searching around on this forum and found an older thread that’s pertinent. Neil Ferreri had a bit of input there. Here’s the link, in case you’re interested.


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