beginner question. XYZ probe diameter. Is this the diameter of the shaft that goes into the collet or the cutting portion of a tool? For example, if I have a quarter inch shaft and the cutting diameter is half inch, which diameter do I enter here? Thank you.
It is the diameter of the cutting/flute portion of the endmill that is selected as this provides the correct offset.
Thank you! I appreciate the support!
Keep in mind that the machine coordinates are for the center of the spindle/bit. When you use the touch probe to set the work (0, 0) to the corner of your material, the machine needs to know how far the spindle is from this corner when the bit touches the probe so that it can calculate the actual location of that corner. That’s why it needs the probe offsets (x and y) and the bit diameter.
There have been a few discussions on probing with V-bits, many saying you cannot probe with them and must change to a straight bit. You can probe with a V-bit if you can lower it enough so the known diameter (max diameter of the bit, or shank) can touch the probe.
I personally do not use the probe much. I usually run a profile pass to cut the final dimension of my projects and have enough extra material, so zeroing on the EXACT corner is not important. I just jog the machine, so the center of whatever bit is installed (including V-bits) is just inside the corner, then manually zero out X and Y.
I would strongly recommend you get a blank to use strictly for probing. Depending on various bit manufacturers to always get their bit’s diameters to exactly what they should be is risky in my opinion. Not to mention the fact that you can’t probe with TBNs or VBits. Cadence MFG, the maker of the popular Jenny bits, makes one here.
XY probing isn’t accurate with a cutting tool. The probe isn’t tall enough to reliably capture the cutter’s edge. Test this yourself with a typical 2 flute spiral mill. Probe it and then send it to the WCS home (0,0) with the jog function. Write down the machine coordinates. Without rotating the spindle, probe again, and jog to 0,0 again. The machine coordinates should be the same. Now rotate the bit 45 degrees and probe a third time. Jog to 0,0. The machine coordinates will be slightly different.
Maybe if the machine probed lower and used more of the block it would work better. It does seem thick enough for the typical endmill. @RTCNC ? Maybe make it settable.
But for now if you want precision, set XY manually with a pointy V bit and then change to your endmill and just reprobe Z (or use the tool setter if you have it set up). Or use a precision blank and probe XYZ and then change to your bit and reprobe Z only.
BTW my block wasn’t “square”. The actual block is square but the distance from the inside lip to the edge is different in X and Y. I had to change the settings in my Redline controller.
I completely agree that probing with form tools is not 100% accurate. Even with straight bits as Roger (@ds53652 ) noted. But I think it’s important for beginners to know how the probing tool works, and how important the degree of accuracy might (or might not be) to them. I can count the number of times when my project was ruined because my zero was off by a fraction of an inch … zero.
There are situations when the accuracy is definitely important. Some people mill soft metals where the tolerances are tighter. Some people also have projects that may take several days, and need to be able to turn off the machine, then reliably set zero again to the same spot after they turn it back on.
There was a post on a Facebook users’ group where someone had a project with a center datum position. They did not know how to set the work zero to the center of their material because they only knew how to use a probe.
@dsunds There was another user who had a toolpath that was created with the datum zero in the back-left. He said that the probe was off when probing from this corner. Like you, his probe was not completely square. I instructed him to switch the probe’s X and Y offsets in the controller, because when measuring at the back-left, he had to turn the probe 90 degrees from his usual orientation.
@newbies : It’s great to have these devices that can automate/simplify tasks, but it’s important to know how they work, and more importantly, how to work without them.
Can you imagine in the future when all machines come with an ATC and Tool Setter, and people will not know how to manually change bits? 
Thank you very much! That is very helpful!
Greg
Yes, I can imagine. Before I retired, I worked in a shop that had 6 machinists and only myself and one other could operate the manual mills and lathes. The others would take time to program the CNC machines to turn a simple round or mill a simple bolt circle. How many modern machinists can run manual machines anymore?
For sure. I have a machinist’s gauge pin. You can get them from Amazon for just a few dollars.
Thank you very much! I will look into that.
I used a 1/4" (actual .245") round steel stock. The probe set x,y,z.
Then I put in the tool and reprobe to just set Z.
I don’t know if it will be reassuring or not, but my son is in one of Connecticut’s technical high schools and while they’ll absolutely be learning to program g-code using Mastercam, the shop has more manual vertical mills and lathes than automated ones.
For the first 1.5 to 2 years they are trained on manual equipment learning to ‘feel’ the machine as I like to say. Then they move up to modified mills that have mild programming capability. They have four or so HASS machines with ATC’s and the like including one 5 axis mill.
I don’t know how much of his manual skills he’ll remember if he pursues the trade, but I think, at least at his school, they’re trying to train young machinists with good foundational skills.