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.
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.
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.
OK - I'm not a blacksmith or anything like it... but hardening this type of steel is quite easy to do. While I use a gas forge:
For tools this size, it's easily done just as well with a MAPP gas torch. You only have to worry about the business end of the tool - the rest of it (what's under the handle) doesn't require any sort of hardness past what it already has. Incidental hardness won't hurt it, and neither will leaving it annealed. After it becomes cherry red, and reaches the "Curie Point" (where it loses any magnetic qualities), quench it in oil. Any oil will do, I use vegetable oil in a coffee can.
When cooled, temper the steel by sticking it in an oven set at 450 degrees for an hour. This should give the blade a hardness of about Rc60 or so...
A black coating covers the steel when you are finished heat treating the blade, but comes off easily with a deburring wheel - or sandpaper if you don't have one of those:
Now you are ready to assemble the whole affair. Well - OK - not quite. Since it's a bit easier to get into the corners, now is a good time to work on the bevel of the knife a little bit, before you put it together. Not that it will be a big deal later, but its just a bit easier to do it now:
I don't sharpen it completely - it won't cut paper - because I don't want to cut myself somewhere in the assembly process. Final sharpening can wait till the whole affair is assembled. Speaking of which, that can start, if you have done all of the shaping you need to do to the scale before putting it together. One example might be ramping the edge of the scale down near the business end of the tool, something you can't do after it's together without a good amount of difficulty.
Now that we are there - it's time to put the rivets into place.
It's a simple process, really - it's just putting the outer sleeve in first, then placing the blade and opposite scale into place, and hammering the rivet into place:
Here's where you find out if you didn't have the right size hole. Too tight, and either it won't go in or crack the wood, or too loose and and it won't hold it tightly enough.
Now that the tools are assembled, it's time for a little quality time with the sander, rounding off the sharp edges. Some of this is better done before the blade is installed, and some is better done afterwards. It's up to you when each shaping step is important - just use common sense in how you approach it, and learn from the mistakes made... and you will do fine. I actually was shaping the handle all the way through the process...
By far the easiest finish is a little boiled linseed oil followed by paste wax. You can add as many coats as you feel necessary to get the sheen you want. So - here they are in all their glory:
Nothing spectacular, but still make for some good, functional tools without spending an inordinate amount of time on them putting them together.
From there, the screwdrivers are ready to use:
For the knives, a little time with some oil stones, sharpening them the same as you would a pocket knife (with a double bevel) is required to get them into shape. Some people might prefer a single bevel for a marking knife, but I would encourage them to give one of these a try. If nothing else, they are good for carving the wheat into the handles you area making for all those backsaws you are making, right?