Hi Chris,
You can read more about it here: XYZ Zeroing plate and tool diameter - #7 by jwoody18
I originally had it made for the ShopBot at MakerLabs here in Vancouver. When using a shared machine under time pressure, the ability to reliably set up your work and recover from issues is really important. Especially when doing full sheet jobs at 4x8 I found the probe and the scripts that go with it and then did a slightly modified spin on it. The scripts Ron Olson wrote for it also put the bit in the center of the circle and prompt for confirmation from the operator that it is correct before retracting.
The biggest benefit, day to day, is the size and weight of the block. The Sienci supplied unit is so small and light that it can easily be pushed off square, this thing isn’t so easily misaligned. Also, with two Z height options, in certain circumstances it is helpful to be able to probe Z on the lower portion. I had to do it one day last week although the exact use case escapes me. Of course you need to adjust your height accordingly since the offset at that point is zero not 12.7.
Ron and I didn’t implement it but we were discussing the fact that the code could be improve to actually detect bit diameter so you didn’t need to worry about remembering to set the correct bit diameter. That’s something that would be welcome. I find the placement of various probe functions (well a lot of functions, actually) in UGS to be quite unintuitive compared to the ShopBot software (which is far from brilliant but makes more sense in some areas).
So really it’s size (weight/stability), the ability to see the corner position centered in the circle and some flexibility with the lower edge. It isn’t something I bought to replace the Sienci one (which I included in my order) it is something I had made while waiting for my machine to use with a specific ShopBot script so I could improve reproducibility and recoverability when using the PRS-Alpha at MakerLabs.
It’s become very clear to me in the past week that recoverability and consistency require homing/limit switches and a solid probing solution - combined with a grid/doghole alignment strategy to position work on the table. I’m getting closer to having my arms around all of this. Next step is playing with the limit switches but I noticed mine are labeled 6V-32V I’m not sure if there is enough juice to drive them off the 5V labeled line on the Longboard. I’m going to pay with them on a Raspberry Pi setup and see what I can do with a bench power supply. If that works and I need to I may just power them separately and only connect the signal pin. Any reason that won’t work?
-Jeff