Dave –
The kind of work I have in mind where a Keats angle-plates could be useful on a mill or drill is in, or on, the ends of cylindrical or square section objects, where it performs the roles of vice and Vee-block in one go.
Recently I needed tap M6 holes in both ends of 18 aluminium bars, using a tapping-head in a bench-drill with low-gear setting. In the end I used a 3-jaw chuck on an adaptor-plate, but could just as easily have used the Keats block. I forget what settled the argument – I think it was the rod diameter a bit too small for the clamp.
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Nick –
There is of course a limit to what the bending tool will take, but also minimum radius to the bend to some extent depending on the material, and I would suggest 2mm thickness the absolute limit.