Busted Geared Hub on der Uber Coker

Der Uber Coker was built up for Kris Holm using a modified Chinese
prototype geared hub with one of Dave Stockton's world's strongest Coker
wheels laced around it. It's been around a bit. Brian MacKenzie, the
bowler formerly known as Sofa had it for awhile and then it went to
Andrew (HardcoreCokerRider) for some speed work. The hub seized when
Andrew was performing a turn at low speed so, fortunately, he wasn't
hurt. He shipped me the wheel and I gutted it leaving the hub laced to
Dave's beautiful wheel.

A segment of one of the planet gears had broken off. It further shredded
the bushing it surrounded spredding some fragments of sintered bronze
through the mechanism. One of the remaining intact planet gear/bushing
assemblies was jammed quite tightly, probably from this detritus.

Some photos of the damage are 'IN THIS GALLERY.'
(http://gallery.unicyclist.com/album621) The way REAL gears are
supposed to look are in photos on 'MY WEBPAGE'
(http://staff.washington.edu/gharper/) in the sections on gears and
bearings and modifications.

My theory is that the cheap, apparently EDM cut gears made by the
Chinese firm were not anywhere near the real gear tolerences specified.
In fact I know that. The planet gear that broke, as well as all the
planet gears, could have their teeth cut too deep so they would fit in
the assembly. This thinned out the effective wall thickness between the
ID and minimum OD of the gear.

We are presently thinking of what will work and what compromises to make
to get the thing going again as soon as possible. I kind of think that I
will have to buy a set of gears that are commercially (and correctly)
made. Then I may want to make a new axle out of hardenable 17-4PH
stainless steel. I would probably need to make a new sun gear bearing
cage, too.


--
harper - TANKED at GASWORKS

-Greg Harper

B L U E S H I F T

"My world view has come crashing down like a drunk clown on a giraffe,
riding through a cactus patch..." -evil-nick on "Entry of the
Gladiators"
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Yeah, and you also need to find some more guinea pigs! Any volunteers?



--
David_Stone
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David Stone is always hot to ride fast. Did you ride that thing when it
was in NY?


--
harper - TANKED at GASWORKS

-Greg Harper

B L U E S H I F T

"My world view has come crashing down like a drunk clown on a giraffe,
riding through a cactus patch..." -evil-nick on "Entry of the
Gladiators"
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harper wrote:
*Some photos of the damage are 'IN THIS GALLERY.'
(http://gallery.unicyclist.com/album621) The way REAL gears are
supposed to look are in photos on 'MY WEBPAGE'
(http://staff.washington.edu/gharper/) in the sections on gears and
bearings and modifications. *

You are right. The photos of the broken gears look nothing like the
ones on your web page. The ones in the new gallery are all blurry and
out of focus. The ones on your web page are sharp clear and look much
better. That's obviously what the problem is. The Chinese gears don't
photograph well.

I predict you'll be getting your Blue Shift back ASAP. Only a fool
would ride that thing now. Maybe we can get Blackwood to ride it on
Sunday.


--
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john_childs wrote:
*
I predict you'll be getting your Blue Shift back ASAP. Only a fool
would ride that thing now. Maybe we can get Blackwood to ride it on
Sunday. *


George has it. Doesn't he qualify? Blue Shift has all of the good
components. The gears are in focus so they work better. It also has a
hard axle.


--
harper - TANKED at GASWORKS

-Greg Harper

B L U E S H I F T

"My world view has come crashing down like a drunk clown on a giraffe,
riding through a cactus patch..." -evil-nick on "Entry of the
Gladiators"
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john_childs wrote:
*Only a fool would ride that thing now. Maybe we can get Blackwood to
ride it on Sunday. *

Bring it on...


--
tomblackwood - Registered Nurtz

Tailgate at your own risk.....

"By George! The man's a genius!"
Murde Mental

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MY AXLE was always hard...


--
unisk8r - One Wheel Wander
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So, I look back on this and see that I received der Uber Coker in May. I
just started doing the maching a couple of weeks ago in my spare time.
Spring and summer are for playing on unicycles, not making unicycles.

I bought commercial automotive gears for the rebuild and modified them
the way I did for BlueShift. I reamed the planet gears to accept press
fit, commercially available, sintered-bronze oil-impregnated bushings
and reamed the bushings to 0.2495". The Chinese planets ran on mild
steel rods. The new ones run on polished, 0.2500", hardened steel dowel
pins. I had to machine a new planet cage because the Chinese one was too
sloppy, was not built correctly, and had unreachable burrs that could
snag moving parts. The dowel holes are 0.0005" undersized for an
interference fit. I peened the dowel pins in two places on each side (5
pins, two sides, 20 peen dimples) to ensure that they remain anchored.

I salvaged the sun gear cage and welded a modified, commercial gear onto
it. It is a full fusion weld rather than a few spot welds like the
Chinese sun assembly.

The ring gear was easy to do. Then I found that the bolt circle in the
Chinese aluminum housing was off a few thousandths for one of the dowel
pins. I reamed that hole out and shimmed that dowel in the ring gear.
The shim is covered with a spacer plate so it can't work its way out of
the ring into the gear teeth.

I machined an axle from 17-4PH stainless steel. I welded the axle to the
planet cage and hardened it to Rockwell 42. Now it is hard enough to be
usable with steel cranks.

When Kris first got the wheel he drilled a hole in a stock Coker frame.
He attached the sun arm (torque arm) to the frame leg with about a 4mm
screw and nut with some spacer washers. It was a good anchor with what
he had on hand. The drilled hole was not quite straight and the 4mm
screw was not to beefy, but Kris doesn't have a machine shop immediately
accessible. I bored a 0.5" hole straight through the leg in the right
place, centered over the tapped hole in the sun arm. I machined a brass
plug with a lip and counterbored for a 6mm screw which matches the
tapped hole in the sun arm. I used 0.100" of brass washers to space the
sun arm. The length of the plug is just a few thousandths less than the
leg tubing thickness so when the assembly is tightened it doesn't crush
the frame tubing. It's a good, beefy anchor.

Not enough of my sissy Seattle unicycling buddies wanted to test it
before I shipped it back to New York. I rode the unicycle a couple of
miles today, tightening the cranks occassionally until they were fully
engaged. I freemounted it on my first try. My second go took me six
tries. My third attempt, I got the freemount on my second try and then
landed it every try from then on. I take a RUNNING start and do a jump
mount when the wheel has some inertia. It is a fast rascal.


--
harper - A walk in the park.

-Greg Harper

B L U E S H I F T

"You guys aren't thinking this through. Hey, where's your other... BANG.
" - Brian MacKenzie
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harper wrote:
*I reamed the planet gears to accept press fit, commercially
available, sintered-bronze oil-impregnated bushings and reamed the
bushings to 0.2495". The Chinese planets ran on mild steel rods. The
new ones run on polished, 0.2500", hardened steel dowel pins. *


Oops. Typo. The holes in the planet cage are reamed to 0.2495" for the
interference fit. The bushings are reamed to 0.2510" to spin freely on
the dowel pins. I also don't know how to spell "machining" as you can
see in my first paragraph.

After riding awhile, I measured the backlash with a dial indicator. It
was 0.023" or a little over 0.5mm with 6" (150mm) cranks. I expect
0.040", or 1mm, from these gears with 6" cranks.


--
harper - A walk in the park.

-Greg Harper

B L U E S H I F T

"You guys aren't thinking this through. Hey, where's your other... BANG.
" - Brian MacKenzie
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