Get a High-Quality Touch Block


Shortly after getting started with CNC, I found myself needing to do parts that required two setups. In this case, I had to cut them from both sides. I made a number of mistakes in how I kept alignment while doing so, and my trouble was complicated by my Onefinity XYZ Touch Probe, which I'll call a touch block from here on out.
In order to accurately align your second setup with your first, you need to register off of consistent geometry. I have dog holes that allow me to register my workpiece against the front and against the left on my first setup. When I flip that part over, the front stays the front, but the left moves to the right. That's all fine. I simply align the right side of the workpiece against the dogs on the second setup.
As a result, if I zero my first setup on my front left corner, I. need to zero my second setup off of the front right corner, which is the same corner.
When I fit the touch block to the front right corner, it's rotated 90 degrees from the position it was in on the front left corner. This means that in the second setup, I'll be zeroing my Y using the left face, which was used to zero the X in the first setup. Similarly, I'll be using the right face to zero the X, which was previously used to zero the Y. If the offsets on the touch block are the same, that's not a problem. Mine aren't. They're off by .34mm.
Ok, so I can enter different values in my Jogging & Offsets screen on the Masso. But, that means I need to swap the values in X and Y every time flip a workpiece. That sucks! What if I forget to swap them back when I'm done? This is just too inviting of problems.
Onefinity support told me they outsource the fabrication of their touch blocks, and that .5mm was within tolerance. I can't accept that. 
With my .34mm difference in offsets, the problem is actually compounded by both axes being off.   My parts will be off by .481mm unless I go through the repeated hassle of swapping the offsets, and invite problems into my setups. No way!
You can see this in the image to the right.  With both edges being off by .34mm, every point is off by a diagonal of .481mm from its intended location.
If you look at the impact in a real world situation, like the bore and counterbore of an M5 cap screw, you can see in this image, that it just won't work.
I replaced my Onefinity touch block with one from 360cnc, which claims a .02mm tolerance, mine is about .005mm off, which could be my measurement error.  I recommend this unit over the Onefinity one. Sorry Onefinity, but yours has poor tolerances.
The good news is, I was able to reuse the banana plug and magnet cable as they're pretty universal. Installation, was as simple as unplugging the Onefinity one, and plugging in the new one. Of course, I also had to change the X and Y offsets to 15mm ONCE. Once and done!
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