Making Frank's Cranks

Finally got around to taking some photos of my process as I make some of my string winding cranks. Here's one with a koa handle:

These cranks feature a soft head made of low density polyethylene, an angle of 83-degrees to simulate wrist rotation, and a solid bearing in the handle.

Interestingly, one of the first questions I get about them is, "How do you achieve that angle?" So, I'll start the description with that in mind. . .

The only commercially made part is the little brass ball, which I drill almost all the way through with a 6.4mm drill that gives me a .252: hole, making for a nice sliding fit for a 1/4" precision ground aluminum rod:


Here, I'm using my tiny Rusnok milling machine. I have the ball set into a matching cavity I milled by plunging with sa 1/2" ball end mill into the steel soft jaws on my old 4" Kurt vise. By the way, I get my soft jaws for vises and chucks from - no affiliation - they sell CNC made jaws for about what I'd pay for raw material.

A single drop of Loctite 609 green bearing retaining compound goes into the hole:


Then the 1.60" long 1/4" aluminum rod:


A gentle but quick squish in the bench vise forces the green compound right out so I can be assured of complete coverage:


It takes overnight for a complete cure, but it sets up in seconds so it can be handled with no chance of loosening.

Here's another view of Kurt's soft jaws, showing the recess I milled to hold the completed assembly for drilling that 83-degree angle hole:


The little crank arm fits right in there:

A #12 drill gives me about .0015" clearance for a slip fit on my 3/16" diameter steel bearing shaft:


My vise mounted bolt cutter chops off sections of 3/16" steel rod, and they shoot all over the place, so I position a few shallow boxes to catch them so I don't actually have to clean off a section of my bench:


Of course, the bolt cutter leaves nasty deformed cut ends, so it's off to the 2x72 belt grinder for a quick bit of squaring up and chamfering:


The cut end on the left becomes the nice smooth one on the right in almost no time:

Then, it's time for another drip of the green Loctite to secure the bearing shaft:

So, here's that 83-degree elbow, after all:

I milled halfway through one so you could see the inside, where the smaller steel shaft runs right through the ball and the 1/4" crank arm, for a solid joint assembly:


A few years ago I had a steel stamp made so I could mark my stuff, and for this project, I made up a special little fixture that holds it with some inset neodymium magnets while I whack it with my classic B.F.H. to get a good impression, right on center:



As they'd say in a previous century, "None Genuine Without This Brand."


The handle bearing starts out as a 2.25" long piece of 1/2" 6061 aluminum rod, and I drill through it with a number 12 drill bit:
That's not the drill bit I actually use - it's a staged photo. I really use a parabolic drill for better chip clearance, and to try to keep things straight and on center, I drill halfway from each end. The #12 bit gives me just enough clearance for the bearing shaft and lubrication.

One end gets a touch with a 90-degree countersink to butt up against the brass ball:

Flipping it around, I turn down the outside of the shaft to 5/16." Gripping the last half inch in the collet, I can just manage to turn down the 1.75" I need without supporting the outboard end:


Switching to a 5/16" collet and gripping up close, I use a 1/4" radius form tool to shape the end of the bearing:


Here's a shot of the stages in making the bearing:


Painting on a thick layer of white lithium grease, I squidge the bearing onto the shaft:


And follow it with a small brass washer, which I make by drilling 1/4" rod (#12 again) and part off in the lathe:


I have a special little drill jig I made from O-1 steel and hardened. It allows me to stick the end of the bearing shaft through the hole and drill a 1/16" hole about .01" from the brass washer. By using this jig, I can accommodate any thickness of washer, or length of bearing, so when I make those parts I don't have any nasty tolerances to hold. I cheat whenever I can:

The drill press is one of those tiny Electro-Mechano precision ones that cost about $1500 direct or in my case, two hundred bucks on eBay. A swell little machine, but it does take a little while to get used to the peculiar pulsing mechanical speed control with its centrifugal governor.

Back to the bench vise to tap in a 1/4" long 1/16" roll pin to retain the assembl;y:

Here's the secret to the handle - I cement it over the bearing, so it looks nice and trim, can't come off, and shows no sign of retaining hardware:


To prepare the bearing for the handle, I run my belt sander super slowly, and ride the bearing on it, holding it at an angle so the coarse grit skids and scuffs a nice pattern on the outside of the bearing:


OK, how about the handle? I make those, too, and I'll post that stuff soon as I have time.

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Like-a this:


String instruments with right-angle gears take a lot of turns to tighten up the string when it's first installed. While string-winding cranks have been available for decades, they are generally pretty cheesy, wobbly, and prone to scratching the delicately finished wood of the headstock. For the last few years, I've been making a series of real professional tools for folks (repairers,roadies, builders, etc.) who do a lot of restringing.
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Frank, Those are super. Changing strings has to be the least favorite part of playing a stringed instrument. Your cranks will make everyone want to change their string more often, just so they can show off your work.
I started making these things a few years ago and took some to give to pals at the luthier conference in Pennsylvania. The response was good, and some folks pressed me to make some for sale. So, I worked out my process and have offered them on the Gryphon web site, in the "Frank's Corner" of the accessories department, where there are a few other things I make in my home shop.

My design, tooling and ability being what they are, this is a labor-intensive process, so as long as I make these myself, they'll probably continue to be the most expensive string winders on the market.
Thanks for the good word! Here's a shot of the three sizes I make - one tiny one dedicated for mandolin, where the clearance is often critical, a medium one for vintage guitars and a large one for more modern tuners: