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:
![koacrankinhand.JPG koacrankinhand.JPG](https://www.hobby-machinist.com/data/attachments/220/220188-9c11fa6a8511e18225622abe71652779.jpg)
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:
![crankarm04.jpg crankarm04.jpg](https://www.hobby-machinist.com/data/attachments/220/220200-a04ae17ca98046c056954565a3c71c4d.jpg)
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:
![crankarm06.jpg crankarm06.jpg](https://www.hobby-machinist.com/data/attachments/220/220202-d081b9070dfe30d6171fb569e52a285b.jpg)
Then the 1.60" long 1/4" aluminum rod:
![crankarm07.jpg crankarm07.jpg](https://www.hobby-machinist.com/data/attachments/220/220203-6a39b28044200d5838b756834691ff4e.jpg)
A gentle but quick squish in the bench vise forces the green compound right out so I can be assured of complete coverage:
![crankarm08.jpg crankarm08.jpg](https://www.hobby-machinist.com/data/attachments/220/220204-95f1f38066b40b37a8349bfb9a0fb396.jpg)
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:
![crankarm10.jpg crankarm10.jpg](https://www.hobby-machinist.com/data/attachments/220/220206-66c5c85de5c549c2fc4346cb2220904f.jpg)
The little crank arm fits right in there:
![crankarm13.jpg crankarm13.jpg](https://www.hobby-machinist.com/data/attachments/220/220207-9e8df0eb0a4bab8f014d83d75ea58b49.jpg)
A #12 drill gives me about .0015" clearance for a slip fit on my 3/16" diameter steel bearing shaft:
![crankarm15.jpg crankarm15.jpg](https://www.hobby-machinist.com/data/attachments/220/220251-e62c1f9b869bcf3871ffe570d7eeb20e.jpg)
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:
![crankarm16.jpg crankarm16.jpg](https://www.hobby-machinist.com/data/attachments/220/220252-31e81ab02d61f63e80e80e383b8ddc4c.jpg)
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:
![crankarm17.jpg crankarm17.jpg](https://www.hobby-machinist.com/data/attachments/220/220254-4f30c349e463abe62f60f6ea7ba063ad.jpg)
The cut end on the left becomes the nice smooth one on the right in almost no time:
![crankarm18.jpg crankarm18.jpg](https://www.hobby-machinist.com/data/attachments/220/220255-0b81863211f2c0a0952eae68d8312f97.jpg)
Then, it's time for another drip of the green Loctite to secure the bearing shaft:
![crankarm19.jpg crankarm19.jpg](https://www.hobby-machinist.com/data/attachments/220/220260-e2ddcf7cbccfada70287360a4163eaba.jpg)
So, here's that 83-degree elbow, after all:
![crankarm21.jpg crankarm21.jpg](https://www.hobby-machinist.com/data/attachments/220/220261-7a3a35c49aa2f21bbc54a2c08f528de3.jpg)
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:
![crankarm22.jpg crankarm22.jpg](https://www.hobby-machinist.com/data/attachments/220/220262-5816741c6e7f8134bf89e96a6a3ddba9.jpg)
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:
![crankarm24.jpg crankarm24.jpg](https://www.hobby-machinist.com/data/attachments/220/220263-9bc835642b7238ab8e6201b0372d6537.jpg)
![crankarm25.jpg crankarm25.jpg](https://www.hobby-machinist.com/data/attachments/220/220264-6e7fddcf0c1e4fe20c21ed87a8b86abc.jpg)
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:
![crankbearing01.jpg crankbearing01.jpg](https://www.hobby-machinist.com/data/attachments/220/220265-af8e0a21756fd54631ec3e6648ed6eef.jpg)
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:
![crankbearing02.jpg crankbearing02.jpg](https://www.hobby-machinist.com/data/attachments/220/220266-f7cc7389564fa163f6e3b397474d01c8.jpg)
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:
![crankbearing03.jpg crankbearing03.jpg](https://www.hobby-machinist.com/data/attachments/220/220267-eb3f97dc5aaad01395c6829e88ef0934.jpg)
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:
![crankbearing04.jpg crankbearing04.jpg](https://www.hobby-machinist.com/data/attachments/220/220268-93238699a9a71690d554976c87540fc2.jpg)
Here's a shot of the stages in making the bearing:
![crankbearing05.jpg crankbearing05.jpg](https://www.hobby-machinist.com/data/attachments/220/220269-ad3b079269af13a7d892a926c3c8a2e5.jpg)
Painting on a thick layer of white lithium grease, I squidge the bearing onto the shaft:
![crankbearing08.jpg crankbearing08.jpg](https://www.hobby-machinist.com/data/attachments/220/220270-40532511f1bf626f4e2b2e17b206d63d.jpg)
And follow it with a small brass washer, which I make by drilling 1/4" rod (#12 again) and part off in the lathe:
![crankbearing09.jpg crankbearing09.jpg](https://www.hobby-machinist.com/data/attachments/220/220271-c89be7ab0dc350a61dbb7e150882972a.jpg)
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:
![crankbearing10.jpg crankbearing10.jpg](https://www.hobby-machinist.com/data/attachments/220/220272-590ff00bcaf9ccb483f63c9df42bae5c.jpg)
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:
![crankbearing11.jpg crankbearing11.jpg](https://www.hobby-machinist.com/data/attachments/220/220273-912a061e7d0ff4737516d23cbb51b0a1.jpg)
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:
![crankbearing12.jpg crankbearing12.jpg](https://www.hobby-machinist.com/data/attachments/220/220274-4800840e350912296008763c37a563d9.jpg)
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:
![crankbearing13.jpg crankbearing13.jpg](https://www.hobby-machinist.com/data/attachments/220/220275-1c8fad8a17dca0a6370bf2c0509487ae.jpg)
OK, how about the handle? I make those, too, and I'll post that stuff soon as I have time.
![crankarm10.jpg crankarm10.jpg](https://www.hobby-machinist.com/data/attachments/220/220205-66c5c85de5c549c2fc4346cb2220904f.jpg)
![koacrankinhand.JPG koacrankinhand.JPG](https://www.hobby-machinist.com/data/attachments/220/220188-9c11fa6a8511e18225622abe71652779.jpg)
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:
![crankarm04.jpg crankarm04.jpg](https://www.hobby-machinist.com/data/attachments/220/220200-a04ae17ca98046c056954565a3c71c4d.jpg)
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:
![crankarm06.jpg crankarm06.jpg](https://www.hobby-machinist.com/data/attachments/220/220202-d081b9070dfe30d6171fb569e52a285b.jpg)
Then the 1.60" long 1/4" aluminum rod:
![crankarm07.jpg crankarm07.jpg](https://www.hobby-machinist.com/data/attachments/220/220203-6a39b28044200d5838b756834691ff4e.jpg)
A gentle but quick squish in the bench vise forces the green compound right out so I can be assured of complete coverage:
![crankarm08.jpg crankarm08.jpg](https://www.hobby-machinist.com/data/attachments/220/220204-95f1f38066b40b37a8349bfb9a0fb396.jpg)
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:
![crankarm10.jpg crankarm10.jpg](https://www.hobby-machinist.com/data/attachments/220/220206-66c5c85de5c549c2fc4346cb2220904f.jpg)
The little crank arm fits right in there:
![crankarm13.jpg crankarm13.jpg](https://www.hobby-machinist.com/data/attachments/220/220207-9e8df0eb0a4bab8f014d83d75ea58b49.jpg)
A #12 drill gives me about .0015" clearance for a slip fit on my 3/16" diameter steel bearing shaft:
![crankarm15.jpg crankarm15.jpg](https://www.hobby-machinist.com/data/attachments/220/220251-e62c1f9b869bcf3871ffe570d7eeb20e.jpg)
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:
![crankarm16.jpg crankarm16.jpg](https://www.hobby-machinist.com/data/attachments/220/220252-31e81ab02d61f63e80e80e383b8ddc4c.jpg)
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:
![crankarm17.jpg crankarm17.jpg](https://www.hobby-machinist.com/data/attachments/220/220254-4f30c349e463abe62f60f6ea7ba063ad.jpg)
The cut end on the left becomes the nice smooth one on the right in almost no time:
![crankarm18.jpg crankarm18.jpg](https://www.hobby-machinist.com/data/attachments/220/220255-0b81863211f2c0a0952eae68d8312f97.jpg)
Then, it's time for another drip of the green Loctite to secure the bearing shaft:
![crankarm19.jpg crankarm19.jpg](https://www.hobby-machinist.com/data/attachments/220/220260-e2ddcf7cbccfada70287360a4163eaba.jpg)
So, here's that 83-degree elbow, after all:
![crankarm21.jpg crankarm21.jpg](https://www.hobby-machinist.com/data/attachments/220/220261-7a3a35c49aa2f21bbc54a2c08f528de3.jpg)
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:
![crankarm22.jpg crankarm22.jpg](https://www.hobby-machinist.com/data/attachments/220/220262-5816741c6e7f8134bf89e96a6a3ddba9.jpg)
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:
![crankarm24.jpg crankarm24.jpg](https://www.hobby-machinist.com/data/attachments/220/220263-9bc835642b7238ab8e6201b0372d6537.jpg)
![crankarm25.jpg crankarm25.jpg](https://www.hobby-machinist.com/data/attachments/220/220264-6e7fddcf0c1e4fe20c21ed87a8b86abc.jpg)
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:
![crankbearing01.jpg crankbearing01.jpg](https://www.hobby-machinist.com/data/attachments/220/220265-af8e0a21756fd54631ec3e6648ed6eef.jpg)
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:
![crankbearing02.jpg crankbearing02.jpg](https://www.hobby-machinist.com/data/attachments/220/220266-f7cc7389564fa163f6e3b397474d01c8.jpg)
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:
![crankbearing03.jpg crankbearing03.jpg](https://www.hobby-machinist.com/data/attachments/220/220267-eb3f97dc5aaad01395c6829e88ef0934.jpg)
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:
![crankbearing04.jpg crankbearing04.jpg](https://www.hobby-machinist.com/data/attachments/220/220268-93238699a9a71690d554976c87540fc2.jpg)
Here's a shot of the stages in making the bearing:
![crankbearing05.jpg crankbearing05.jpg](https://www.hobby-machinist.com/data/attachments/220/220269-ad3b079269af13a7d892a926c3c8a2e5.jpg)
Painting on a thick layer of white lithium grease, I squidge the bearing onto the shaft:
![crankbearing08.jpg crankbearing08.jpg](https://www.hobby-machinist.com/data/attachments/220/220270-40532511f1bf626f4e2b2e17b206d63d.jpg)
And follow it with a small brass washer, which I make by drilling 1/4" rod (#12 again) and part off in the lathe:
![crankbearing09.jpg crankbearing09.jpg](https://www.hobby-machinist.com/data/attachments/220/220271-c89be7ab0dc350a61dbb7e150882972a.jpg)
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:
![crankbearing10.jpg crankbearing10.jpg](https://www.hobby-machinist.com/data/attachments/220/220272-590ff00bcaf9ccb483f63c9df42bae5c.jpg)
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:
![crankbearing11.jpg crankbearing11.jpg](https://www.hobby-machinist.com/data/attachments/220/220273-912a061e7d0ff4737516d23cbb51b0a1.jpg)
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:
![crankbearing12.jpg crankbearing12.jpg](https://www.hobby-machinist.com/data/attachments/220/220274-4800840e350912296008763c37a563d9.jpg)
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:
![crankbearing13.jpg crankbearing13.jpg](https://www.hobby-machinist.com/data/attachments/220/220275-1c8fad8a17dca0a6370bf2c0509487ae.jpg)
OK, how about the handle? I make those, too, and I'll post that stuff soon as I have time.
![crankarm10.jpg crankarm10.jpg](https://www.hobby-machinist.com/data/attachments/220/220205-66c5c85de5c549c2fc4346cb2220904f.jpg)
Last edited: