Seems like the design wasn’t tested on slippery stock.
I think they do the extra X&Y outer probes to take the diameter of the bit into account.
A soft solution for people who don’t like the movement might be to allow the probe diameter to be entered into Carbide Motion and just have it do the “push against the stock” probes. Oh, to better support the Raspberry Pi of course 
I agree about the mouth of the alligator! There have been too many times when complacency has resulted in injury 
I agree, but it’s better to keep hands away from moving parts. Ask any Combat Engineer with his index finger missing from constructing a Bailey bridge!
Bit of a tangent, sorry 
I guess the dowel would be more accurate, but wouldn’t that be the case for the v1 if a dowel was used with that?
I think it’s a force (Newtons) thing. With the v2, there is no resistance to the push - other than your hand - making it very easy to move the BitZero, but with the v1 it’s pushing against the stock.
It’s a small thing, really. The reasons I’m happier with v2 is the magnet rather than the alligator clip (fixable with a little time and effort) and not having to earth it separately.
That’s my opinion, anyway
My concern using the dowels is that it requires one more tool change.
I have bad wrists and I suffer through the tool changes.
All that aside and all things being equal, the BitZero should function correctly. If the connectivity between the probe and the hole is poor, it will affect accuracy if unnoticed, or time out if pushed too far and requiring everything to be re-initialised. This wouldn’t necessarily be an issue with the v1.
Thanks for the lesson, though 
Im very new here and to cnc. My question is If you use the dowel supplied with the bit zero and then change… lets say to a 1/4 end mill… would the different bit change the zero?
Hey Tim!
Yes, it would change the zero.
With respect to Z, the only position the machine knows is the vertical position of the spindle. It knows this because it’s been sending it up and down instructions from the last time it was “homed”.
So long as the up and down instructions have resulted in movement, and it’s not been driven into something that prevented movement, it’s pretty sure it knows where the spindle should be.
However, it has no knowledge of where the BitZero is, or how long the thing in the spindle is.
In truth, you could pull off the spoilboard, suspend the machine on legs, and put a 1 metre dowel in the spindle and put the BitZero on the floor. It wouldn’t know it was a metre away. Just that the spindle is a fixed number of “ticks” from the homing position.
So if you took out that 1 metre long dowel and put in a 10cm bit, and then tried to run your job, it would have no idea where the bit was cutting. Just that you told it to move the spindle to a particular position for your project’s zero.
Soo… long story short - the Shapeoko has no idea where the zero physically is in space. Just where the spindle was when you said “this is zero”.
OK, I’m going to make myself look stupid, here…
When you use the dowel, it ‘touches’ the inside edges of the hole (left, right, back, front) and from those movements measures the centrepoint of the hole, which is the corner of the workpiece.
In my mind, this would be the same centre of the end mill you put in the spindle, surely?
You would need to re do the Z height manually, unless you had a BitSetter to do it automagically.
That’s correct. X and Y should be fine.
Most people have issues with zeroing Z, particularly when changing a bit and the finding cuts are too shallow or too deep.
This could randomly be true. 
If you look at the cutting end of your typical endmill, you can see that it isn’t a circle, but the cutting teeth are arranged in a circle. So, while it cuts a circle it isn’t actually a completely round end. Right?
The dowel does have a completely round end.
So, when doing a zero trip around the inside of that BitZero depression, an endmill may exactly touch at its radius, but then it may be oriented in such a way that it touches in between cutting edges and that would be a smaller radius. The zero may be off.
A dowel doesn’t have that smaller radius. It is round. It zeros inside that depression the same everywhere it touches. See?
You? Pedantic? Never happen! 
You’re correct, though. I should have been a bit more specific and try to keep it simple.
As far as I understand it, the BitZero does what it should do, but at any time the bit (or dowel) is changed, the Z height needs to be re-zeroed. The X and Y should remain the same unless you move or change the workpiece, unless you’ve got a guide in place for repetitive work, for example.
I think CM does know. If there is a requirement to change the cutting bit during a project, you’d need a separate toolpath for each bit, and re-adjust the Z height before each new cut. With a BitSetter installed, CM understands the bit change, prompts for it, then pings it over to the BitSetter to re-zero the Z height before continuing with the next toolpath.
Again (me being pedantic, this time!) I don’t think it will matter. If the BitZero is doing it’s job properly (and only the designer of the BitZero can confirm this, really) it should find the corner of the workpiece, irrespective of how big the dowel is (as long as it fits inside the hole!) The cutting bit can be larger or smaller than the probe, because it’s the toolpath that determines where the cuts are made, based on the tools geometry. To extrapolate on @CrookedWoodTex comment, using a dowel will provide a more accurate corner of the workpiece than an endmill.
And this is why, without a BitSetter, separate toolpaths are necessary and, therefore, resetting the Z height for each bit change.
Good morning!
I think the two sizes of dowel are provided for convenience, so you’d use the one appropriate to the shank size of the bit, rather than accuracy?
This thread is beginning to look like a @jepho vs @NewToThis discussion, although I think we’re generally of the same opinion
Anyone else prepared to comment?
It’s possible the two sizes are provided for different collets rather than for any accuracy.
The measurement inside the circle should be sufficient for the machine to figure out the size of the dowel and therefore compensate for that to estimate the XY centre.
I agree that the calculation is harder with a bigger dowel since it can touch the edges of the circle in a complex way.
I think the thing that is currently a circular hole in BitZero 2 should in fact be a square hole. Maybe in BitZero 3?
Well, I commented, but it was not discussed further. 
Your discussion here seems more like a critique of the design of the BitZero-2. @Gerry is correct; the different dowel sizes are a convenience so you can do your zeroing without changing collets.
One thing to be sure you do is wipe down the contact surfaces occasionally. Sawdust is an insulator, the zero “hole” will catch dust, and you will get into a re-initialization situation quickly.
The only thing further I have is that you should get the BitSetter without hesitation. You can use CM without it (by zeroing traditionally), but CM will still have a few innocuous prompts about zeroing and changing bits, etc. Just don’t activate BitSetter in the Settings.
The circle should make for very simple calculations which are minimized if the BitZero is placed at an angle.
A square hole would only work if the unit were placed perfectly squarely everytime and would magnify any deviation from square.
It probably is, with the ‘moving about’ issue, but I suppose I was trying to get my head around the accuracy thing - and wether I was being a bit dim understanding it. Happily not, though
Oh yes, without a doubt! It makes life much easier - and more automated
Erm, but why would you not do that?
Referring to the situation where one did not have a BitSetter.
Actually, I disable my BitSetter (and clear all offsets) when I use a 1" diameter surfacing bit. It won’t physically fit my BitSetter in its standard configuration. (There is a thread here about adding a large diameter disc to the plunger for that situation.)
No offense meant by my comments.