CM536 Corner Probe puzzlement

What are SO3 users doing to get consistent X/Y Corner Probes? I have seen inconsistent measurements and after looking at my 1/4" end mill and using a caliper to measure the end mill across the diagonals, I get 3/4" when measuring across the two flutes and 3/8" when measuring without the flutes. Doesn’t this get inconsistent X/Y when doing the Corner Probe and either the flutes contacts the probe or the non-flute end contacts the probe? Do users manually rotate the end mill to get the same surface to hit the probe? I have gone to using a broken 1/4" shank end mill (got lots of these) and using the shank end to touch the probe so that I get a 1/4" touch no matter the orientation of the end mill. If this is confusing then it is only because I am too!

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Not confusing at all, it’s a real concern, which is why C3D probes now ship with 1/4" and 1/8" dowel pins, that you can use to probe X/Y accurately, and then you swap in the actual tool you will be using and probe Z only (or if you have a bitsetter, you just probe X/Y/Z with the pin, and later swap to the real tool at the start of the job)


I use an old single flute 1/4”end mill that needed to be replaced. I chopped it off at the transition point where the shank meets the cutter and chuck it upside down in the router collet, instant 1/4” probe pin.

Some bits are smaller above the cutting teeth. Plus most bits spiral up/down and you might get the measurement at its thinest part. When you probe you tell cm what size the bit like 1/4 inch #201. The probe assumes the full 1/4 inch to calculate the corner so with less than 1/4 inch bit you get the wrong measurement.

It’s probably not the diameter of the ‘probe’ that’s important, if you use a broken cutter, just the fact it’s perfectly round :+1:

Warning: never use calipers on an endmill’s flutes, it damages them. See this thread for discussion, which includes explanation from John from PreciseBits (they make endmills).

If you have reason to precisely measure the diameter of the endmill, the best way to do it for hobbyists like us is to cut a square pillar using the endmill and then measure the size of it.


I think the probe routine has to subtract the probe’s radius from the position it contacts the BitZero in order to calculate where the zero is. It’s probably important accuracy-wise that this exactly matches the size of the tool the probe routine prompts you for.

Since the hole is round, the diameter/radius of the tool used doesn’t matter — the two extremes are compared, and the halfway point is used

I didn’t see BitZero v2 specifically referenced. I must have missed that.

There’s no hole in my BitZero so, at least for it, I can’t see how the radius doesn’t matter.


Correct, my description was specific to the BitZero v2 when probing for an axis in the hole.

For the BitZero v1 (formerly known as the Carbide 3D Touch Probe) endmill diameter always matters, save for Z, which is invariant for either.

So (throws small plastic hand grenade) why supply two probes?

My guess would be the ER11 on the Nomad supports only 1/8" by default, and the whatever-the-router-is on the Shapeoko needs a 1/4" sticky-thing.


For convenience so that folks don’t need to switch collets when switching from a probing pin to the actual tool (says the guy who also bought an 8mm one and will eventually have to round out the set if he ever starts using metric or 3/16" tooling).