Wow!!! That is very impressive. I make a lot of stuff out of wood, but metalworking is on a whole nother level. Excellent work.

I was after a slightly larger tap wrench, one that could hold taps ranging from about M5 to M16 or so. I have a couple of cheap and cheerful Chineseum tap wrenches that generally suck, so I decided to make a better one. As far as tap wrenches go, you really can't go past the Starrett 91 series of tap wrenches. With that in mind, I found a length of 1" bar and set to work. The first step was to create the knurlled handles. Both handles were done in a single operation, resulting in a consistent knurl and handle diameter.   From there, the center diameter is turned and the shape of the handles roughed out to ~45deg angles. After that, my radius cutter is used to turn an 8mm radius on each end of the fixed handle.   The main bar is then cut to rough length and the opposite end turned down. The minor diameter of the handles is 9mm, which just allows for clearance of the M10x1.0 threads. This end was roughed out, single point threaded then the radius turned on the inside edge.    A long hole was drilled into the threaded end of the handle. This hole will eventually extend into the tap holder, but for the moment I stopped short a few mm so that I would not create an asymmetric interrupted cut when drilling the hole. A random long series parabolic 5mm drill bit that I stumbled upon one day came in handy here.  Meanwhile, the other handle was drilled to depth and tapped M10x1.0. The 9mm hole in this handle extends much of the way through the handle to provide space for the spring.  With the majority of the lathe work done, it was off to the mill. The main body of the wrench was clamped and the cheeks cut off. First roughed out with an end mill, then the last ~0.5mm taken down with the fly cutter to give a very nice surface finish.  The main tap hole was drilled (13mm) and the majority of the Vee was taken down with files using some small V-blocks as guides (I super glued some steel shims on the V-block faces to prevent the file from marring them).  After this, the hole down the handle could be drilled through into the opening. Unsatisfied with the squareness and finish of the filed surface, I jerry rigged up a plunge broach tool by modifying a big old bolt I had lying around. This was drilled out to a snug fit for a 10mm square lathe tool blank which was sharpened and polished. Much stuffing around and many light cuts later, the Vee was cut satisfactorily.  The plunger was made from an old M6 bolt. A small length of thread was left on the top, onto which a small slug of brass was threaded and fixed with red lock-tite. This end was turned down to fit into the handle end. The length was trimmed to meet the faces of the Vee when the spring (which came off either a nasal spray bottle or a shampoo bottle, I never throw springs away) was fully compressed.  The next step was to cut a Vee in the end of the plunger. To do this, I clamped it in a split block of aluminium (the threaded section will be used later), this was mounted at a 45 deg. angle and the end milled until the Vee reached a tangent on both sides.  The threaded section of the split clamp was used to securely hold the threaded end horizontal in the mill vise so that an 11mm slot, 2mm wide, could be cut towards the top of the threads. This will constrain the alignment pin that prevents the plunger from spinning when the wrench is tightened.  The slot was milled with a 2mm carbide ball nose endmill going full depth of cut in one sphincter clenching pass. This is the only 2mm end mill I have, so if I break it, I'd have to buy another one and wait for it to get here.  With the slot milled, the plunger was clamped at its maximum extension and a 2mm hole drilled partially through it to take the guide pin.  The guide pin, a ~6mm length of random 2mm wire that was slightly filed down on one end to give a sliding fit in the slot, was tapped into the hole. I really hope I don't need to take that out. Luckily, it seated just below the threads and was a snug but free moving fit.  All that's left to do is to thread on the handle and stick a tap in it and it's done.