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 monsterjaws.com - 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."

NEXT UP IS THE ALUMINUM BEARING FOR THE HANDLE . . . . . . .


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.

 

I really like the handle material! Is it a bakelite material?

 

I get my plastic handle material from the guys that supply pen turners. I really like the crazy acrylics the best, although I also currently use acrylic stabilized hardwoods. Bakelite is a particularly cool older style of plastic, but not as available as the more modern acrylics.

Check out these, with the multi-colored chips - we call it "clown barf:"



It's fun stuff to turn, and it smells sweet and fruity. Mostly the chips come off as loooong curly strings, but some of it can make quite a snowdrift on the lathe. Here I'm turning a short piece between centers, using my shop-made "drive center."

 

My crank handles start out either as hardwood, often acrylic-stabilized figured woods, or as solid acrylic plastic (my favorite). I get the stuff from the suppliers that pen turners use, in the standard size of 3/4 x 3/4 square. The usual pen blanks are five inches long, but some of the suppliers, such as Bear Tooth Woods in Colorado have been helpful in their willingness to supply me seven-inch pieces. My crank handles are 3-1/2" long, so I can get two from each 7-inch blank. Sometimes I'll use full meter-long sections to maximize the yeild vs. price.

Here's the blank:



Unfortunately the through hole in my lathe chuck won't pass the full square, so I have to knock the corners off before I do anything else. I have a simple little wood fixture with a v-groove to make the job go quickly on my venerable Delta 14" vertical bandsaw:




And, now for the star of the show - my two-jaw chuck. I bought this chuck off eBay partly because I didn't know such things existed, and I'm a real sucker for any tool I don't yet have. Like about ten percent of the tools I buy this way, I actually found a real use for this one in fairly short order. It has big soft jaws, and I cut them to ninety degree V-shape so they will hold a square piece on center. Unlike a four jaw scroll chuck, it grips the piece solidly on center even if it's not a perfect square. That's important to me because these blanks aren't quite a regular square:



I suppose most pen turners work between centers, or at least have the right end supported with a tailstock center. I rely on a good, solid grip with the two jaws to be able to turn all the way to the end without support:



I'm using a standard taper attachment on the lathe, and I keep it set at this angle as long as possible so I can not only repeat the handle turnings but also make fixtures and bore collets to hold the handles for various operations. I can produce the taper with two passes using a high-positive rake aluminum cutting carbide insert. I turn the taper on the end, reverse the stock in the chuck, and turn the other end to have a double ended tapered blank

Back over to the band saw to cut the blank in half:





In order to shape the rounded end of the handle, I bored an "emergency" soft collet to the exact taper, using an upside-down boring bar and the lathe in reverse:

It holds the taper rigidly with good concentricity:



A standard 3/8" radius form tool knocks off the square bits and makes a nice rounded end on my 3/4" diameter handle:


A little cleanup with 220 grit aluminum oxide open coat stearated abrasive paper:




Now comes the weird part. For some reason I decided it would be best to drill the handles after they are formed, so I made and bored some tall soft jaws for a cheap Chinese three-jaw chuck. Concentricity isn't an issue because I bored the jaws to the diameter I'd be using:



What you can't see in the photo is a depth stop I have mounted inside the spindle, and up into the chuck. It keeps the workpiece from slipping backward if I get to aggressive with the drilling.

This photo shows a standard split point drill, but these days I use a parabolic flute drill. If you haven't tried parabolic flute drills, you should! They allow chips to flow back out so much more freely than regular twist drills.


A bit of medium viscosity cyanoacrylate will adhere the handle to the bearing very nicely:



I try not to get my fingers stuck when I shove the handle in place:




I made a simple fixture to hold the handles in my bench vise. It's aluminum, and it has two holes I bored with the lathe and taper attachment. One grips the fat end, the other the skinny end, with clearance for the arm and ball:



The fixture as two aligning pins, and neodymium magnets on the outside to stick to the vise jaws:




A bit of the "Chatanooga Shoeshine Boy" action with various grit abrasive paper, finishing at 400 smooths over any lathe marks, and softens the transition to the rounded end:




A serious key to good appearance is the blending of the aluminum bearing section to the handle. With the fat end in the vise, I can accomplish that with the same strip sanding action:



Years ago I modified my 1 hp. Baldor buffer to accommodate two buffs on each end. Here I'm using the brown coarse/medium Menzerna plastic compound to cut through the sanding scratches:



The final buff is with Menzerna fine P175 on the wider wheel:

Notice that the right edge of the wheel is turning black from contact with the aluminum bearing as it shines both aluminum and plastic to a high gloss.

Handle complete, like-a this:

 

I just realized I had some photos I'd left out of the first long post - shots of making those little brass washers. After drilling the 1/4" rod about an inch and a half deep with #12 drill, I simply parted off a bunch of rings, around 1/32' thick, simply moving the carriage and judging thickness by eye. To keep the tiny washers from flying across the room, I held a piece of 1/16" welding rod in the hole to catch them:


Here's the parting tool I ground from a 1/8" high speed steel blank. The cutoff blade is barely .024" wide, and sharpened to a fine point so it cuts off a washer neatly without a bur. As the blade proceeds inward, it cleans off the cut end of the rod, eliminating a bur there, too:





That way I end up with a batch of ready-to use washers that don't need any cleanup at all:

 

The business end of the crank starts out as 1" diameter 6061 aluminum. I use the 14" Delta band saw to cut pieces roughly .95" long.



One of the best things about having a lever collet closer is how quickly you can pop identical pieces in and out. Here, I'm facing one end:




Next, I lock the carriage and using a collet stop, reverse the pieces and trim the other end to final length of 0.90."




I find it much quicker to use the mill to cut the recess for the plastic crank head, so I use the soft jaws bored for the job and plunge a 3/4" end mill right on center:




Here are some right off the mill:




Back on the lathe, a quick little chamfer to break that sharp edge at the hole:




It's just a touch, but it really helps inserting the plastic piece, and allows the parts to mate up nicely:



Now, reversed in the collet, I plunge into the part with a shop-made radius form tool to finish the detail:




This is a simple little drill jig I made up to space three spring pin holes accurately:



I just butt the part up against a simple stop, rotate the jig so it sits on a flat, and drill the holes right through:




After trying all kinds of different materials, I settled on low-density polyethylene for the crank head because it is the softest material I can machine easily to get a good finish. This is a shot of turning the part that will insert into the body of the crank:



I lock the lathe carriage and the cross slide, so I can use just the compound to plunge into exact depth quickly and accurately.


Over at the bench vise with my magnetic plywood/leather soft jaws in place, I press the plastic head into the body. I make 'em a tight fit so it takes a fair squish to press it up tight. Then, a 1/16" x 5/16" roll pin goes right in with a couple of hammer bumps and a lick with a 1/16 pin punch to seat each pin flush:



I call my bench vise my SEVEN INCH WILTON because right after I bought it I decided to "improve" it for my needs by making some new jaws, and ended up with a versatile too that works really well for me. I don't do heavy work, and have never returned to the original hardened toothy jaws.


One more trip over to the lathe to trim the circumference (if needed) and to bevel the front edge a bit:


And back to the soft jaws on the mill. In order to keep the slot in the head aligned with the crank arm, I made up a little handle that's a simple 1/4" plug with a 1/8" rod sticking out. When I close the vise, it grips only the aluminum crank body, of course:


A plunge with a ball end mill and a couple of back-and-forth trips give me a nice slot for the guitar tuner button:


For the slotting operation I set hard stops on the mill so I can do the job repetitively with no error.

A bit more of the magic Loctite:



And, if I'm careful, the handle goes in straight, and another string winder crank rolls off the ol' assembly line:



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Wow...I've looked at that handle a few times in the past couple of weeks Frank. I had no idea this was such a great and informative thread. Thanks for posting and I love your handles. You are a true craftsman. Beautiful work sir.

 

Wow they look great! Looks like a lot of work in all the jigs. But you have it down to a science.

 

Lotta work everywhere - jigs, machining, jamming in ansd out of collets, and assembly - made about 700 or so at this point. . .

 

I like the Koa!

 

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:

View attachment 263069

Beautiful work!