I had a dilemma the other day : My carve started out with a V-Bit and as I brought the spindle over to the Touch Probe I realized I did not know what value to use for the diameter. To avoid the issue I changed the carve tool path so 1/4 inch end mill was first. Am I missing something with the V-Bit, any other suggestions on what diameter to use for a V-Bit when measuring XYZ? TIA!!
Your solution was correct. Always use a straight bit to determine your XY origin.
Though, you can always find the origin with a straight endmill, then swap to a v-bit and probe Z, if you’re running a v-carve only toolpath.
Hey Mark,
For better accuracy I use this gage
and Z probe after
I am learning slowly, I give myself credit this time though since something didn’t look right when I tried to do the xy with the v-bit. Thanks Dan for the details here !!!
I will acquire one asap. Thanks Hubert for the recommendation !!
why go with the .2” ? Most of my bits are 1/4”
The diameter you use for probing XY doesn’t matter as long as you input it correctly in the interface. It’s just trying to find the reference for the center of the spindle, so if you use .2, it will do the touch off and subtract .1 from where it sensed the touch and that will be spindle center. After that point, any tooling you put in the machine will have reference between the cutting edges and the spindle center which is used to ensure you are only cutting as deeply into your xy surfaces as your g-code calls for.
There’s absolutely no reason you can’t use a .25” reference if you’re more comfortable with that. In fact when I was taught to reference with a Shaper Origin, the suggestion was to take a 60º 1/4” shaft engraving bit and put it in the collet upside down (pointy side up), and that gave, at least for our purposes, an accurate enough 1/4” reference shaft. The cutting flutes are short enough on engraving bits that I never experienced any damage to the cutting surfaces nor the collets. Some people may not be comfortable with that techinique though, or are looking for something that is ground to a much higher degree of precision (or is it accuracy? Ahh, my high school math teachers are hanging their heads in shame at me from heaven.)
Cheers.
Another option for a reference shaft is 1/4” x 2 Steel Dowel Pin - 5 of them for $9.99. Very close tolerance dowels.
Consider cutting the flutes off an 1/8” drill bit, leaving just the precisely sized shaft of the drill bit. While not ground to precision, I would think it’s absolutely accurate enough for our woodworking applications.
makes a ton of sense thank you
You can probe with a V-bit if the angled section is shallower than the height of the touch probe. Lower the spindle until part of the vertical portion of the bit (green section in pic) is below the top of the probe (red line). You will need to know the diameter at this vertical section and set it on your controller.
If you’re working with material slightly larger than the finished product (ie. you’ll have a profile cut), I wouldn’t even bother with the touch probe. Place the tip of your bit at the corner of your material and manually set your x/y zero. This should be “close enough” 
. All you really care about is that all your tool paths are within the boundary of the physical material.