what is this used for?

[RobertB]

Article in Machinery Vol. 30 about its use rack and pinion tool slide

 

[The Model A Guy]

Perfect, thank you for sharing its purpose. On to see if I can piece it back into a useful tool.

 

[Silverbullet]

I'd say it's the table for a small hand mill , single operation type. The lever handle gives it away.