Edge finder probe

Some cool applications that I know of are to verify that a part is within some specification, to verify that the part was.correctly loaded in the machine, verify stock size before machining and resetting the zero after some operations have cleared away excess stock unearthing a feature that you can more reliably probe.

All of those aren’t that important for hobbyists though because we have to manually change the tool to probe.l and can be manually performed if needed.

I would like to hear other uses though.

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The most common in-process measuring would be to dial in a high-tolerance feature, by size and/or location. Say I have a 0.627" +0.002/-0.000 hole to make. I would program it something like…

X0.1883 Y0 (Start of undersize circle)
G3 X0.1883 Y0 I-0.1883 J0 (Circle)
G0 Z4.0 M0 (Retract & Stop)
(Measure the hole)
(Subtract the difference between actual & nominal and store in a variable $500)
X0.1885 + $500 Y0 (Final hole size adjusted for discrepancy)
(Cut the circle again…)

FYI, to do that now without cutter comp, I just program a series of passes starting at -0.0020" and incrementing by 0.0004" with a Retract Stop between each pass. Manually measure the hole after each pass, and when it’s within tolerance just stop the program.


Ok, so my probe arrived and so far it works better than expected! Seems to be well built. I followed @ChrisPro’s pinout for the mini-XLR jack (thanks!).

I played around with it for a bit, then managed to write quick user macros in Carbide Motion for probing an internal corner (X- Y-), which solves my immediate need. I still need to check if the combined XY macro properly stores the offsets for both X and Y. And try to measure the accuracy and repeatability.

The downside is that Carbide Motion shows incorrect coordinates on the left side of the window.

So far a definite thumbs up, but we’ll see how well Carbide Motion will tolerate this.

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Some observations after using the probe for a couple of days. After measuring the deflection (0.0685mm for my probe), my little user macro can now reliably probe an internal corner in XYZ. The repeatability of this probe is impressive: I believe the main limitation at this point is Nomad’s mechanical precision.

Here is the macro I’m using (sorry for the weird format, but I’m pasting this out of CM’s actions.json file, because CM won’t let me access my macros unless a cutter is connected :man_facepalming:):

            "G38.2 F40 X-15",
            "G10 L20 P1 X0.9315",
            "G0 X3",
            "G38.2 F40 Y-15",
            "G10 L20 P1 Y0.9315",
            "G0 Y3",
            "G0 Z8",
            "G0 X-5 Y0",
            "G38.2 F40 Z-20",
            "G10 L20 P1 Z9.875",
            "G0 Z50"

Now, this works really good for X and Y, but not so much for Z. I mean, it does set Z very precisely, but it gets messed up after a tool change. One thing I haven’t checked yet: is it possible that the tool depth probe and my probe are wired to the same input? This would cause my probe to trigger before the tool length sensor and mess up the results. The other hypothesis is that it’s simply the probe’s slight deflection in Z that causes issues, but the errors I’m seeing are much larger than that. I’m still not sure what’s going on here.

I plan to try G38.4 probing (away from the stock) and compare results assuming the Nomad can do G38.4, but really what I’m getting right now is quite good already.

Also, as I’m switching between the “Jog” and “Run” screens in CM and hitting bottom buttons on both, I can’t help but wonder about the moment when I’ll accidentally click the “SPINDLE ON” button (can it be disabled?). That will be a suboptimal turn of events.

They’re both probes and connected to the same input.

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check out the gSender thread for a probe “tool length” macro, it might give you some ideas on how to implement something in carbide motion. or tempt you away from it. lol

That would explain my messed-up Z after a tool change. It means I have to be careful to disconnect the touch probe when first installing it or when Nomad initializes itself and measures the tool length. I’ll try that and see what happens!

Having checked today, Z probing works fine if I’m careful to disconnect the probe before the Nomad measures it.

I’m not sure I trust it, though. It relies on the probe flexing the same amount in response to the bitsetter spring, both can (and likely do) change with temperature and over time. I ran several cycles and experimentally determined that if I set Z+0.235 instead of Z0 when probing, I’ll get the right 0 (to the precision of pin+paper check, at least), but I don’t think that will be a reliable result.

Also, I don’t think I need much more from Carbide Motion. The user macros work fine. I mean, it would be nice to get fewer “Are you sure” prompts (for running a user macro or whenever switching to the “Jog” tab). These get very annoying over time and seem rather pointless when I can ruin my day much quicker by clicking the “SPINDLE ON” button, which does NOT prompt you, just turns the spindle on. But other than that, things work fine.

To summarize: the probe is really nice, I get as much precision as I need in X and Y, and Z will probably never be as precise/repeatable because of the way Nomad probes the tool length.

And to sum up, here is the probing macro for X- Y- Z- probing (I’m using two perpendicular gauge blocks to form the corner):

G38.2 F40 X-15
G10 L20 P1 X0.9315
G0 X2
G38.2 F40 Y-15
G10 L20 P1 Y0.9315
G0 Y2
G0 Z7
G0 X-4 Y0
G38.2 F40 Z-20
G10 L20 P1 Z+0.235
G0 Z10
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im not sure if you could use concept this with carbide motion, but I created this little pad that sits next to my BitSetter and is a known height so I can tap that with the probe, and set the tool length rather than having to worry about any deflection from the probe on the bitsetter.

I dont think the carbide user macros would be able to do the math to calculate the offset, but i havent tried it so i dont know.

@rb_designs This

This makes a lot of sense! Unfortunately, it seems that Carbide Motion won’t be able to make use of that kind of setup, so it’s pretty much a no-no in my case.

I guess I’ll stick to probing Z manually, Carbide Motion being the limiting factor here.

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thats a bummer. honestly the change from CM to gSender isnt all that bad. and you dont have the SPINDLE ON button hanging out where you could press it accidentally.

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