Inside Frank’s Cranks, Part 3

mosaic-walnut-cranks
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The 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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Coming soon, Part 4: the “business end” that grips the tuner, and final assembly. . . .



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