Why? Wear of the cap-iron is not a problem, there are plenty of 100 yr old planes (like my 5 1/2) with original cap-irons still doing yeoman service. The biggest enemy of a cap iron (apart from folks with files) is corrosion. For that reason, and because it comes with a nice, clean surface & is more readily available to me in 2-2.5mm thick plate, I prefer to use stainless steel when making cap-irons. It's a little harder on hacksaw blades & files, but at least the finished product remains shiny & smooth.
You can do the job quite easily with hand tools. You will need a tap to match your existing screw. The threads seem to have varied a bit over the years, but I've found an M8 tap will often do. It's not a perfect match, but for the turn & a half of thread in a 2mm thick iron, it's usually close enough to a match (try it on a piece of scrap before committing to the real thing, of course).
A single-bend cap iron like the Hock & Veritas is very simple to make. You can make the bend in a vise & clean it up with files. If you use a heavier gauge like 3-3.2mm, strive for the "right" fit, i.e. just enough bend to ensure a close fit against the back of the blade, but not so much it turns it into a banana when you tighten the screw down, like this:
By carefully filing & lapping the edge, you can get it to fit nicely without flexing the blade more than slightly. The older, thinner blades are especially prone to flexing.
I think that's why the original caps are made of thin (~1.75mm) steel and have a 'double bend'. The bulk of the CI sits flat on the blade & causes no flexing when tightened up, like this:
I've made a simple jig for bending cap-irons:
It's rather Heath-Robinson-ish, and fussy to set up for bending, especially for a skewed iron which this one is being readied for :
The bend is then made in a vise:
It would be a lot of bother to make a jig like this for just one cap-iron, I think I'd settle for the single-bend type for a one-off. Made carefully, they works as well as the double-bent version.
Needless to say, it's wise to do the bend and finesse the fit before laying out & making the screw & cam slots; that way you have a precise edge from which to work.
Cheers,
Ian
