I have been following the thread on adapting a Tire Tread Gauge as a mini DRO. I often have the need for measuring the length of cut on some of the items I make. I have been making do with a 0 ~ 1" dial indicator but have found that the length of travel can be somewhat constraining. As a "work around" I came up with this design.
Thumbing through a tool catalog I ran across a digital depth gauge by iGaging. It is also 0 ~ 1" but it comes with extensions to allow measuring a hole up to 4" deep. It also has in internal return spring. It cost me $17.50 including shipping.
My approach was to mount the gauge in such a manner that it could be swung away to allow the carriage to move away from the chuck with jamming the device. It also had to be repeatable. My testing showed that I could repeat with no more than .0005" error over 10 raising and lowering cycles. Actually 2 of the 10 showed the error. the other 8 were spot on.
I started by making 2 identical clamping blocks that fit vee rail on my lathe. Only one of the blocks actually clamped onto the ways. The other one was fastened to the gauge to ensure accurate locating after moving. I decided on a 6" bar between the two clamp blocks. I used 3/4 X 1/4" aluminum bar. To ensure the maximum repeatability I used a precision ball bearing liberated from an old hard drive for the hinge.
These pictures should help explain the project.
Here is the various parts before assembly.

Here it is mounted on the lathe. With no extensions I have approx. .850" usable measurement.

With an extension added I can get a total travel of 1.056". With both extensions in use I can move the carriage approx. 9" from the normal work location with the gauge raised.

Here the gauge is swung away to allow the carriage to move away from the chuck.

I am very pleased with the results of this project and am planning to adapt the gauge to measure the cross feed travel also. I will post this when I have all the details worked out.