The Making of: Frank’s Cranks

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I have been making these string winders for a few years now, and here at the shop they’ve been a point of conversation over their various features and styles.  Once folks find out that I actually do all the operations myself, the most popular question is, “How do you make the eighty-three degree angle for the handle?”

So, just for fun, I thought I’d post some photos of the process.

 

First, I drill a 1/2″ diameter brass ball, which I have clamped in a little recess I made in the jaws of my milling machine vise so the ball can be held securely without damage, and the drill will go through right on center:

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After I drill the brass ball to accept the 1/4″ diameter aluminum crank arm, I apply a small drop of a special Loctite retaining compound.  This anaerobic adhesive is catalyzed in the presence of metal, and in this application, achieves about the same strength as an interference, or press-fit:

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And I insert the rod into the hole, where the green compound will lock it permanently in place within a few seconds:

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Then it’s over to my tiny Rusnok milling machine to drill the ball for that 83-degree handle bearing.  In order to achieve repetitive alignment, I’ve milled a pair of “soft jaws” in the mill vise to hold the rod and ball assembly with rigidity and precision in a cavity that exactly matches its profile:

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pearlyellow

New for 2018 – Matched Sets of Acrylic Handle Cranks!

 

Then, a vertical drilling operation gives me that angle automatically:

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The bearing shaft is a 3-inch piece of 3/16″ diameter steel rod, cut from 6-foot lengths.  I use a vise mounted bolt cutter:

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When I clip them, the pieces shoot all over the place, so I position a few shallow boxes downrange to avoid actually having to clean off the workbench.

In fact, those pieces come off with really rough cut ends, so I spend a few moments squaring them up and chamfering sharp corners on my belt sander:

 

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Another drop of that magic green fluid secures the 3/16″ diameter steel bearing:

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Here’s a cutaway view of the final assembly – note that the smaller rod is drilled through both the ball and the larger rod, making the joint incredibly solid and secure:

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Once the arm is assembled, I can hold it in my special little fixture that keeps it aligned while I whack it with a steel stamp:

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None genuine without this brand:

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koacrank

New for 2018 – Figured Koa Handle Cranks!

 

 

 

 

I see the handle bearing as the heart of my string winder crank.  It’s critical to the stability of the action, making it effortless to turn the tuner button quickly and smoothly without wobbling or slipping.   The 3/16″ diameter steel shaft is strong and solid, and I want the bearing and handle to revolve with very little  play or uneven movement.

 

The bearing itself is made of solid aluminum, starting out as a 1/2″ diameter rod, a little over two inches long to provide solid support for the bearing shaft and handle, which is basically a cover mounted over the bearing.  The first operation is to drill the rod all the way through to accept the bearing shaft:

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I do that operation on the lathe halfway through from each end to be sure that the drill ends up right in the center, all the way through the bearing.

Then, I use a ninety degree countersink to bevel the hole at the end that will contact the brass ball:

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I can grip one end of the bearing in the lathe collet and turn the outer diameter down to 5/16,” leaving half an inch at the full original diameter:

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Switching to a 5/16″ lathe collet, I grip the bearing by its smaller diameter, and use a 1/4″ radius  “form tool” to turn the profile in the end that will contact the brass ball, giving it a nice trim look”

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Here’s a shot of the different stages of machining the bearing so far, drilled and profiled:

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Some nice clean white grease will provide long-term lubrication.  I paint the grease on the shaft, press the bearing into position and make sure it turns freely:

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Next, I slip on a tiny brass washer.  I have to make those little ones myself because of their unique size and thickness:

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Here’s a bit of the washer making process –

 

After drilling the brass rod an inch and a half deep, I slice off little rings while holding a 1/16″ diameter steel rod in the hole, so the washers slide onto the rod rather than flying across the room:

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My little parting tool is one I made for this job by grinding it from a 1/8″ high speed steel tool blank  – it’s barely .024″ wide, and it has a sharp bevel on the front end so it cuts off the washer and trims the remaining end of the rod as it slides past:

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As you can see, the washers are rather nicely finished right off the machine:

 

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In order to retain the bearing on the shaft, I drill a hole in the end, right up against the brass washer as I press the shaft through my special little steel fixture that guides the drill right on center:

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I drill it this way so I can press the bearing tightly against the brass ball and take up any lateral play.  That saves me from having to deal with super critical measurement of the bearing length or thickness of the brass washer.

 

I grip the end of the shaft and tap a short pin through the hole to retain the bearing on the shaft.

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With the handle bearing mounted and pinned, I can slip the handle of my choice over the bearing with some glue to hold it, and I’ll have a neat handle that won’t come loose and fall off.  And, there’s no external hardware to clutter up the trim look of things.

 

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The decorative crank handles start out as 3/4″ x 3/4″ x 7″ long square acrylic (or hardwood) bars.  I get the material from the folks who supply artisinal fountain pen makers:

 

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In order to fit the bar into my lathe chuck, I need to knock off the corners, so I use  simple wood fixture on my band saw:

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I have a special two-jaw chuck for my lathe for which I made some special jaws with a square recess to hold the bars.  even if the bar isn’t precisely square the chuck holds it very tightly and  on center:

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Using my lathe’s taper attachment, I can turn the end of the bar into a nice taper in two or three passes with a super sharp carbide tool:

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Reversing the bar in the chuck, I turn the other end to a matching taper, then back over at the band saw, I cut bar in half to make two handles:

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Taper is done, but the ends are still square, of course:

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I keep the taper attachment set to the same angle so I can make fixtures and accessories for the crank handle production.  Here, I’m sticking a handle into a collet I bored to match the taper so it can be held for further work:

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Now, I can form the round end by plunging in a matching 3/8″ radius form tool, neatly cutting the end into a nice 3/4″ diameter hemisphere:

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With the lathe kicked up to high speed, a bit of sandpaper makes quick work of blending and smoothing the round end of the handle:

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I have another special chuck – this one is a three-jaw with special top sections I made so I could bore them to fit the exact taper of the handle, to hold it by the fat end.  I drill a 5/16″ hole in the handle to accept the bearing.   Drilling this way in the lathe assures me that the hole will be concentric with the long axis of the handle, so it will rotate nicely:

 

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The bearing is held on the shaft by the pin in the end, which will be covered completely once I glue the handle in place with a bit of medium viscosity cyanoacrylate adhesive:

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The adhesive starts to set after a few seconds, so I can finish up right away:

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And, this is another fixture I made by boring on the lathe using the taper attachment, still set to match the crank handle taper:

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It has magnets set into the outside surfaces so it can stick to my bench vise jaws, and a pair of tapered holes, one to hold the handle from the skinny end, one from the fat end:

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With the handle held by the narrow end, I can use strips of sandpaper to smooth and even out any lathe tool marks:

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And, most importantly, I can ease the transition between the handle material and the aluminum bearing to give it a nice seamless look:

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I have a pair of cotton flannel buffing wheels mounted on my high speed buffing machine.  First, with the brown heavy plastic cutting compound to even out all the sanding scratches:

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Next, a trip on the adjacent wheel with the super fine buffing compound to bring up a nice high gloss shine:

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The completed handle, with bearing and arm attached – starting to look “real” at last:

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The business end, or body of the crank starts out as a section of one-inch diameter aluminum rod.  I cut the aluminum to pieces a bit less than an inch long:

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On the lathe, I face off one end of each piece, then reverse the piece, and face the other end to a  consistent .90″ length:

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The lathe leaves a nice finish on the ends

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I have some holes bored in my vise jaws to accommodate the crank body as I plunge a 3/4″ end mill to create the recess that will hold the plastic crank head in place:

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The end mill makes a nice clean flat bottomed hole right on center, thanks to the alignment of the vise and machine spindle:

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Back to the lathe to cut a small chamfer on the edge of the hole:

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Even this tiny bevel is enough to facilitate pressing in the plastic part:

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After a bit of cleanup of the exterior of the cylinder, I stick it back in the lathe to use a shop-made rounded form tool to produce the final shape of the crank body:

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I made up this little holder to guide the drill and align three holes around the perimeter of the crank body:

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By simply bumping up against a solid stop, I can hold the piece in place as I drill the  1/6″ holes:

 

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After trying quite a number of different materials, I finally settled on low density polyethylene for the crank head because it’s soft and resilient, yet hard enough that I can machine it to a nice looking finish.  Here, I’m cutting the diameter down to go into the 3/4″ hole in the crank body:

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I make it a tight fit, so I need to press it with the big bench vise to seat it up tightly, and then I tap in 5/16″ long steel pins that go through the holes in the aluminum and directly into the plastic head.

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A quick trip to the lathe to true up any errors in concentricity, and bevel the front edge a bit:

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In order to align the slot in the head with the crank arm, I made a little tool that sticks into the crank arm hole and is trapped by the vise as I close it and grip the crank body for the last milling operation:

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I plunge a ball end mill down, and run it back and fort to produce the correct size slot for the tuner buttons:

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One more drop of the Loctite green compound:

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And, a few seconds after inserting the handle arm into the hole, I have a finished crank. . .

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Written By Frank Ford

Frank is one of Gryphon’s Founding Flounders, and heads our repair dept. He has over 45 years experience repairing and restoring guitars, mandolins, banjos and ukes. He’s also an encyclopedia of musical instrument knowledge, from how they’re made, and how they break to how to make them whole and…

More By Frank Ford

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