I have just restored a 1940’s Marples jack plane and the only thing that wouldn’t work was closing the gap between the cap iron and the cutting iron. The problem turned out to be a twist in the cutting iron, so that the gap was closed when first assembling the two pieces but opened up when tightening the screw.
Does anyone have any experience with this and how to fix it? Do I just try tapping the iron with a mallet on a piece of softwood?
There is a difference between bent And twisted.
Twisted it might be better to tighten the vise on it or clamp one end and CAREFULLY twist it around with a crescent wrench.
If bent tapping on it away from the edge may straighten it.