This is a Joe Pie tool. I'm sure most people already know about these - another tool I have been meaning to make for a while.
I have this Edge Technologies tool - and once set up (bubble is adjustable) it works great. you hold the shaft in the chuck of course, and rest the flat on the tip of the tool you are setting and set the bubble.
All well and good, but there are times you need to set a tool up and don't want to disturb what's in the chuck.
So I made this tool, which is simply a cylinder machined accurately to length to sit on the cross slide, to match the center height of the spindle.
I measured the center height by putting a pin gauge in the chuck, then using a height gauge to measure to the top of the pin gauge, and then from that position to the cross slide.
Don't forget to subtract half the pin diameter from the measurement.
Then a cylinder is turned to that length. I made a top cap to bolt to it on an off center hole - which is to be used to set the height of upside down tools, such as threading tools for reverse threading.
Finished tool looks like this:
Use the razor blade technique to verify the tool is at the right height - scrape the razor blade lightly from height tool to cutting tool. You can feel very easily when the tool just goes from too high to the right height.
Cheap and easy - works really well.
This goes on the cross slide in order to get a nice stable surface, but you could easily make one to reference to flat ways of course.
You can also use it by resting the top cap on top of the cutting tool and adjusting until the gauge sits flat on the cross slide.
I find this easier and more accurate to use than setting the tool tip against a dead center, for example.