Third hand tool

It is a useful tool but I don’t see the need to cut out the end with the sliding rod. Leaving that end at full width adds more support and takes less effort to fabricate. I doubt that the extra drag would be noticeable.

The machinist does a lot of concentric drilling by mounting the part in the drill chuck and mounting the drill in a table mounted chuck. I may have missed this, but a way to align the two chucks is to mount a rod in the top chuck, lower it into the bottom chuck before it is clamped to the table. Tighten both chucks. Then clamp the bottom chuck down and remove the rod. The two chucks are now axially aligned.

Third hand tool - video