Riveted Split Nut Screwdrivers and Carving / Marking Knives
Here is a version of a split nut screwdriver appropriate for most classic split nuts, using a thin blade at its core. Thinner steels are not very well suited when using a tang to hold it in the handle. A better method for thinner steels is to rivet the two sides of a handle (or scales, as they are known to knife makers and blade smiths) onto each side of a blade that runs its full length, like the wooden scales on a steak knife.
Now, I am no master blade smith (more like a bleating novice, to tell the truth), so may commit a great deal of heresy to those schooled in that discipline. If you are one of those, look away now! My main focus for doing this is to show a simple and economic way of constructing simple tools in a wood shop, with tools available to most woodworkers.
Also, since the construction is similar and since I wanted to try making a couple marking/carving knives, so I will document those being made here in the same article. If you are interested in genuine blade smithing, I would point you to a few excellent online sources, including knivesby.com (look for the tutorials link) and also to read the articles on knife making by Terry Primos at primosknives.com. They give a much more in-depth and complete presentation, far beyond my abilities.
Cutting out the Blank.
I chose to use O1 tool steel for this job - while in it's annealed state, its easy to work, and is hardened easily in the home shop using a small forge or even MAPP gas.
I've already made some tanged screwdrivers in an earlier article. These are the second version of these screwdrivers, and have thinner steel that I think will be more useful to the vintage tool enthusiast who may run across the occasional split nut that needs to be removed or installed. I start out with some 1/32" thick by 3/4" wide O-1 tool steel about 6" long. I'll make three in this batch, so I started by ganging all three blanks together in the vise and laying out the width of the slot and the width of the nut onto the blanks:
Then cut the slot out with a hacksaw, knock out the center pieces, and file the bottom of the slot flat:
I leave the width alone for now - I'll narrow the end down later after the blade and scales are mated, so both are the same.
For the carving knife, I just cut out the shape of the head of the knife that protrudes beyond the handle using a hacksaw:
For the knives, I used some 5/8" wide by 1/16" thick O-1 tool steel I had on hand. Had I ordered some specifically for this project, I think a wider blank to begin with, say at least 3/4", would be better. But as this is what I had on hand, I decided to give it a go.
You need a good, stable wood to use as scales for handles such as these. You can use stabilized wood (or wood products) similar to those used by penmakers and the like - I chose simply to go with a dense wood and leave it at that. This is meant to be a simple tool, not a collector's item - so the less time, money, and effort put into it the better off I am. You may follow your rainbows if you like, however. I chose bloodwood for the scales of my tools:
It's a nice, heavy, dense wood, quite suitable for handles. Other woods might include rosewoods (cocobolo), ebony, Pau Ferro - most dense, oily exotic woods are probably suitable, so long as they aren't prone to cracking easily. I cut each scale to the width of the steel blank, then to about 1/4" thickness.
Something else you'll need, obviously, are rivets. Brass rivets, available from Lee Valley (among others) are suitable for this type of project and are inexpensive as well. Careful of the size - there should be enough room for the rivet to mate, but not so much as to let the rivet bottom out.
The size of the hole for the rivets are important - too small and the rivet won't fit (obviously) and if it's too large, the rivet won't grab. Here's a table I ran across that has the hole sizes for standard rivets - though make sure you check your own first:
From here, I drill the holes for the rivets (including countersinking for the head of the rivet!), then bolt the blades into the scales using a screw that fits in the same hole so I can shape the edges on the sander:
You'll probably also notice in some later photos that I number the scales and put corresponding stamps in the blades - I kept getting confused, so that was the only way I could keep them all straight. And that was with only 5 blades! Imagine if I had to do more...
Anyway, I cut off what I could with a hacksaw, then shaped the rest of the handle and knife together on a belt sander - at least for the outside shape of the tool. It's easier to do it now than to wait until the steel is hardened - when it would be very difficult to shape the steel. Now is a good time to narrow the end of the screwdrivers so they fit into the intended split nuts, somewhere between 1/2" and 9/16" is a good figure. It's best to have one of the nuts you intend to use it on to check it against.
One Last Thing Before Hardening the Steel
While the screwdrivers are ready for hardening, one additional step that needs to be done before hardening the knives is to remove the majority of the material at the knife's edge:
I don't remove the steel down to a point at the edge, as that will overheat in the forge. But it's a lot easier to get at least a good portion of the steel off now, before it's hard, than to do it later. So, I establish the basic bevel I want, leaving it a bit thick for finishing up after the steel is hard.