Making a Cap Iron Screwdriver

How do you spell cap iron anyway?  Two words? One word? Hyphenated?  Maybe I should just say chip breaker.

Recently I saw a Bill Carter video and on his bench was a cap iron screwdriver.  Seems like I'd seen him talk about it (though I can't recall where) and he espoused the virtue of using it rather than using the lever cap to uncouple the cap iron from the plane iron.  I've been using my lever caps for almost 15 years without any chips to the lever cap, but I thought I'd make a special screwdriver for this task.

I roughed out the shape on paper and found an over-length piece of scrap wood to use for the handle.  I also found an old hinge leaf to shape into the blade.

Some initial thoughts and some steel for the blade.
These weren't the final measurements, but they were close.

I started with some careful layout on the wood blank and removed a bunch of material with saw and chisel.  Then it went on my bungee lathe to turn the ferrule post and the "waist" of the driver.

Shaping the front end of the handle on the bungee lathe

While I had the bungee lathe set up, I also turned a small piece of dowel so that one end would fit tightly into a brass plumbing adapter and the other end would fit into my drill.  The plumbing adapter would later become a ferrule.

Brass barb to thread adapter (most of barb end has already been cut off)

At first I thought I'd be able to file the barb end with it chucked into my drill, but it turned out to be far easier to file it while clamped in a metal working vise.

Here's the adapter with mandrel stuck into one end

And chucked into the drill

Filing while in the drill was not optimal - too much flex of the drill

So I just filed it while held in a vise

then sanded and polished it smooth and shiny in the drill

I cut off 5/8" length of the smoothed brass adapter and fit it to the ferrule post.  I sawed and filed a slot in the post for a good fit to the screwdriver blade.  I didn't get any pictures of it, but I filed the piece of steel hinge to the proper shape to fit into the ferrule post.  It's 5/8" wide at the business end to fit a cap iron screw full width.  It's a bit wider where it meets the ferrule and fits that nicely with no sharp edges protruding.  I also rounded the tip of the bit, since the slots in cap iron screws are made with a circular blade and are a little deeper in the center than at the ends.

Put a slight curve on the tip

After several coats of shellac, sanding between some coats, then a rub with 0000 steel wool followed by some paste wax, the handle feels very nice and looks great.

And here it is, ready for service

Fits perfectly

I did have to grind the tip a little to get a good fit in the slot.  The hinge metal was about 3/32" thick and the slot is about 1/16" wide.

Another very satisfying project for sure.  Now I'll never have to worry about the lever caps chipping - that is, if I can break my old habit of using the lever cap and start using this new screwdriver!