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High Tech?
Banjo Wrenches
© Frank Ford, 2008;
Photos by FF
Banjos have a couple dozen brackets that hold the head tension,
and on many old timers there isn't much clearance between the shell of the
banjo and the nuts:
The nuts come in a variety of different styles, some of which require a deep socket to grip them well. The traditional wrench is a cheesy little affair that looks a bit like an old clock key:
So, after forty years of twiddling those little keys, I thought I'd join the modern age and make up some special deep sockets I could use with my regular cordless screwdriver for quick disassembly and with a handle for sensitive torque control.
If you count imported instruments, there are four basic hex nut sizes: 1/4", 9/32", 5/16" and 6 mm. I had some 3/8" and 1/2" diameter cold rolled steel stock to use for this project, so I selected 1/2" diameter for the 5/16" wrenches and 3/8" for the other three sizes.
First, I cut a bunch of blanks and milled the hex driver section on their ends:
As you can see, I'm using a collet stop not only to make each one the same length, but also as a way of preventing the milling forces from shoving the stock deeper into the collet and out of alignment. The orange clamp hold a simple work stop of aluminum against the vise jaw end, so I could index the collet block as I loosened the vise and rotated the block after milling each face. With the quill, knee, and X-axis locked, I could mill all my blanks without having to readjust any settings.
Now, on the lathe, I used a single tool to face and chamfer the hex ends:
Below is the tool I used - you can see it is a standard insert holder from which I'd ground some extra relief away for a previous project. That left a considerable overhang of the insert - handy for facing:
One facet of the insert presents at forty-five degrees, so it's perfect for chamfering the ens of the shank:
And for making a nice transition from the hex section to the round:
Next I used a round end form tool to make a groove for the screwdriver's bit retaining chuck:
Here's a close-up of the form tool I made, another leftover from a previous project:
Any time I make up a form tool, I leave it in a tool holder for future jobs. It saves a lot of time to have them loaded, set to center and ready for use. Of course that means I end up with a lot of holders - here's what it's come to by now:
This is one of two drawers I've accumulated. It's a trick I learned from Jim Olsen, and a couple of other guitar maker friends. They set up a router to cut a specific size and depth, lock everything down and never change anything. A separate router for each operation as needed. Last I talked to Jim, he had well over a hundred routers, and was still adding to the collection. As they say, "Routers are cheap - time isn't."
And, after a while, I had myself a nice batch of tool blanks:
Center drilling the end. I set the collet stop to allow quite a bit of overhang because I wanted to be able to work with a lot of clearance, and I wouldn't be doing any heavy turning:
Drilling to the nominal diameter - in this case, 1/4"
Cutting a bit of a step in the end to center the broach:
Plunging in with the rotary broach:
Marking the size on the shaft:
I'd made up this little holder to help align number punches when marking round things.
Here's what the marking looked like:
A quick trip back on the lathe and a few strokes with a smooth file:
Makes all the difference in appearance:
Broaching a blind hole leaves a bunch of compacted chips where the broach stops, even if it's way before the bottom of the hole:
It's hard to judge the depth of the hole in the photo above, but the broached
section is .63" deep.
Another jab with the nominal size drill breaks the chips right out, leaving a nice deep socket.
I turned down the diameter of the 5/16" wrench to .420 to have a nice thin wall, and reduced the diameter of both the 1/4" and 6 mm ones, too:
A little Chatanooga Shoe Shine action with 320 grit emery cloth, and the job's done:
Here's the completed assortment:
I learned long ago that while marked sizes are handy, it's also good to have other cues for quick identification as I reach for tools. So, I made sure that the turned sections were also easy to spot. It's also easy to spot the fact that I did the 9/32" wrenches on a different day - hence the "number alignment issue."
Once I set up to make these wrenches I realized I'd probably want to have some spares, and maybe a few for friends. And, while I was at it, I set aside some "blamks" with only the hex section formed - for future tool ideas, or whatever.
So, into the vibratory tumbler for a nice polishing:
Years ago I bought a bunch of these nicely turned rosewood handles which had suffered on the trip from India. Their brass ferrules were seriously stained. Instead of polishing them, the importer "closed them out" for fifty cents each. What could I do? I grabbed them all, of course!
I chucked the handle in the lathe and supported the ferrule end with a live center:
Oh, and a strip cut from a steel tomato sauce can was just perfect for protecting the handle from chuck jaw imprints:
I cut a bit off the diameter in the center and plunged a parting tool almost all the way through:
Off the lathe, I simply broke off the excess length.
Naturally it's about impossible to center up a squirmy thing like this in the chuck without a bit of help. I just used an empty tool holder, and with the lathe running, brought it in to force the part to run true - quick and easy, just like that:
With the handle running straight, I had no trouble drilling concentrically for an insert to accept my new tools:
The insert is a piece of 7/16"diameter brass with a 1/4" hole drilled through it, then broached to 1/4" hex:
A 1/4" rare earth magnet went right down into the hole
Tapped down into the hole and secured with a small drip of cyanoacrylate, the magnet went right down past the end of the broached section so it could hold my new tools in the handle:
Glued into the handle:
Now, back on the lathe to finish the contour:
This time I'm driving the handle with a regular hex bit held in a collet, and using a cup center to support the rounded end.
With my wood chisels and a simple rest, I smoothed out the end of the handle:
After a bit of quick sanding on the lathe, I did a bit of "faux French polishing" using cyanoacrylate and a small rag while the piece was spinning at 1200 RPM.
The finished tool:
And a little holder for the set:
Here it is in action:
