MUni hub design

> Anybody have any comments about this design idea?

I think turning the hub from a single block of steel is overkill. I’ve never
seen the flanges fail. In my experience, unicycle hubs always break between the
bearing and the crank. I believe the one you had last fall at MUni Weekend may
have failed in a different way, but it was built differently from common
unicycle hubs, I think.

I would imagine that hub flanges could be welded onto whatever kind of axle you
can make out of indestructible stuff. After watching Trials experts at the Sea
Otter Classic on Sunday, I’ve seen what they do/use and we must be able to make
something similar for us.

Can hub flanges be welded onto a high-end trials crankset?

BTW, I hate to bring this up, but as long as you’re making and writing about
them, I’m pretty sure on both sides of the border it’s spelled “axle”.

Stay on top,

John Foss, the Uni-Cyclone http://www.unicycling.com

Hi,

Over the last few months I’ve been experimenting with a couple of different hub
designs, to try to design an extremely strong hub capable of withstanding huge
drops. Thus far the most success I’ve had is with having a solid hub machined
(turned on a lathe) out of a 3.5" diameter solid rod of 4140 steel (so the
flanges are one-piece with the rest of the hub- no welding or press-fitting). I
took a Fishbone “Big Ass” crankset, which consists of huge tubular 175 cm
cranks, and a 20 mm thick 8 spline bottom bracket axel (22 mm outside the
splines), cut the axel in half and welded the stubs into holes drilled in the
end of the hub.

The last one made this way lasted for about 1.5 months before the axel twisted
and the weld broke when going off a big drop. Partly it failed due to improper
heat treatment after welding.

I’m building another similar one just so I can ride ASAP, but I had an idea I
wanted to throw out:

  1. Turn a similar hub on a lathe.

  2. Have a gearmaker spline a long section of rod to match the spline pattern on
    the cranks, and have them also machine a keyway (square groove) between one
    of the splines (or miss a spline if necessary to make room for the keyway.
    Chop the long section into appropriate lengths, so you have lots of spares.
    Make this out of a super strong alloy like 3312 steel.

  3. drill the hub out at press-fit size, with a keyway groove cut in the inside
    of the hole to match that on the axel.

  4. tap the axel into the hub, so the keyways line up, and tap a key into
    the keyway.

  5. heat treat everything to appropriate Rockwell values.

You would now have a strong hub with a replaceable axel for the next
time it broke.

Where I live (Vancouver BC) there are several gearmakers that have told me that
this would be feasible (within the $200 to $300 CAN$ range). They also indicated
that the alternate solution, internally splining the hub, would be
unrealistically expensive and that keyways are used in lots of other extremely
high torque applications.

Anybody have any comments about this design idea?

Kris.


Kris Holm, B.Sc. Geologist, Forestry Group, EBA Engineering Consultants Ltd.
Suite 550, Sun Life Plaza, 1100 Melville Street, Vancouver, B.C. V6E 4A6
Tel:(604) 685-0275 Fax:(604) 684-6241 Email: kholm@eba.ca

RE: MUni hub design

Okay, Okay, I always seem to spell axle wrong!

The reason for the one-piece axel (just joking- axle) was logistics. A friend
has access to a good metal lathe, but doesn’t know how to weld, so it was less
expensive, if more time consuming, to make a one-piece design.

“Trials experts” break stuff all the time and have similar problems to MUni- the
Norco Factory Trials Team has designed and is designing custom stuff for
themselves because they break stock components. North Shore (technical downhill)
riders here in Vancouver also break tons of stuff; I’ve been on lots of rides
where at least one person breaks a bottom bracket. Talking to Race-Face Cranks
Ltd. in Vancouver, they said that the bottom bracket designs on standard bikes
are on the small side for hardcore use, but that they are forced to design
cranksets for this size because it is simply that, a standard size.

Since MUni is much harder on axles than bikes, especially than full-suspension
bikes, I really think that a replaceable axle is a good idea.

At 08:31 AM 3/24/99 -0800, you wrote:
>> Anybody have any comments about this design idea?
>
>I think turning the hub from a single block of steel is overkill. I’ve never
>seen the flanges fail. In my experience, unicycle hubs always break between the
>bearing and the crank. I believe the one you had last fall at MUni Weekend may
>have failed in a different way, but it was built differently from common
>unicycle hubs, I think.
>
>I would imagine that hub flanges could be welded onto whatever kind of axle you
>can make out of indestructible stuff. After watching Trials experts at the Sea
>Otter Classic on Sunday, I’ve seen what they do/use and we must be able to make
>something similar for us.
>
>Can hub flanges be welded onto a high-end trials crankset?
>
>BTW, I hate to bring this up, but as long as you’re making and writing about
>them, I’m pretty sure on both sides of the border it’s spelled “axle”.
>
>Stay on top,
>
>John Foss, the Uni-Cyclone http://www.unicycling.com
>


Kris Holm, B.Sc. Geologist, Forestry Group, EBA Engineering Consultants Ltd.
Suite 550, Sun Life Plaza, 1100 Melville Street, Vancouver, B.C. V6E 4A6
Tel:(604) 685-0275 Fax:(604) 684-6241 Email: kholm@eba.ca


Kris Holm, B.Sc. Geologist, Forestry Group, EBA Engineering Consultants Ltd.
Suite 550, Sun Life Plaza, 1100 Melville Street, Vancouver, B.C. V6E 4A6
Tel:(604) 685-0275 Fax:(604) 684-6241 Email: kholm@eba.ca

RE: MUni hub design

> Each rider individually puts no more weight on their cranks and bottom bracket
> than on a regular mountain bike. Sure, the wheel hubs are stronger but since
> the axel inside the crank arm is usually the limiting factor, I think that BMX
> type splined systems are the way to go.
>
> >Out of curiousity, wouldn’t the hubs or hub shells made for
> MTB tandems
> >have sufficent strength? Since they’re designed to support
> two riders
> >they should be good enough for a single rider MUni. Or am I missing
> >something?

There are two primary forces that work to destroy unicycle axles:

  1. Shock force - jumping down from high places, and sometimes landing with all
    your force on one foot puts tremendous strain at the axle. This can stress
    the axle in either direction, depending on your foot position as you land.

  2. Cranking force - Just plain riding up and downill, you’re using (at least
    some of the itme) all the strength you have and it all goes through the axle.
    Unlike on a bicycle, this force is applied in both directions. That’s why
    screwed-on sprockets don’t work on giraffes, and traditional crank attaching
    methods (cotter pins or cotterless) are prone to failure.

Both of the above forces work over time to fatigue the metal and eventually
break it. By using harder metals, and more volume of metal in the high-stress
areas, the axle will last longer. For riders like Kris, separating the axle from
the hub is also a good idea, because I think Kris will always break them, no
matter what!

My advice to anyone doing custom work, think in terms of making 50 or 100. How
much would they cost? I unfortunately can only use hubs with the same width
dimensions as a Miyata, so please make it that size, okay?

Stay on top,

John Foss, the Uni-Cyclone http://www.unicycling.com

RE: MUni hub design

> A while back I heard that Phil Wood, who’s company makes MTB hubs and other
> items, made some proto-type unicycle hubs. He was looking for a company that
> produces unicycles to see if there is enough interest.
>
> If he has enough interest to have made a prototype, then maybe he would be
> interested enough to deal with the issues surrounding producing a hub strong
> enough for riding off road.

The problem is that an axle strong enough for us MUni heads would probably
require a different set of cranks and bearing holders as well. And the number of
riders requiring this extra strength is still very small, probably not enough to
justify any kind of mass production. Even as MUni becomes more popular the
numbers will likely always be small, but hopefully we will someday reach a point
where someone can manufacture some really good stuff for us!

jf

Re: MUni hub design

Brett

> >I think turning the hub from a single block of steel is overkill.
>
> I would disagree. Making a one piece hub is highly advantageous. I
have
> had an axle fail at the inside of the flange weld. This is presumably
due
> to the weld heat stress on the steal. Granted, it was probably not properly
> heat treated, but nonetheless, any welding invariable weakens
the
> piece. I have been told that it could be cost effective to make a
single
> unit axle in small quantities. Making straight flanges on a single
piece
> axle would not be difficult. But the flanges need to be angled to
match
> the angle of the spoke. I don’t know much about machining, but I
can’t
> imagine that it would be real easy to machine a flange with a very
slight
> inward angle. From what I’ve picked up, the flange angle and the axle

> splinning would be the most challenging parts of the axle.

Angled flanges are just produced by just turning the head stock slightly and
using the drive on it. Doing the spoke holes is just tedious, it requites a
rotary or indexed table and angling the head on your miller… oh yes, and a
bit of time.

Cheers

Roger

Re: MUni hub design

Out of curiousity, wouldn’t the hubs or hub shells made for MTB tandems have
sufficent strength? Since they’re designed to support two riders they should be
good enough for a single rider MUni. Or am I missing something? Jim

Foss, JohnX wrote:
>
> > Anybody have any comments about this design idea?
>
> I think turning the hub from a single block of steel is overkill. I’ve never
> seen the flanges fail. In my experience, unicycle hubs always break between
> the bearing and the crank. I believe the one you had last fall at MUni Weekend
> may have failed in a different way, but it was built differently from common
> unicycle hubs, I think.
>
> I would imagine that hub flanges could be welded onto whatever kind of axle
> you can make out of indestructible stuff. After watching Trials experts at the
> Sea Otter Classic on Sunday, I’ve seen what they do/use and we must be able to
> make something similar for us.
>
> Can hub flanges be welded onto a high-end trials crankset?
>
> BTW, I hate to bring this up, but as long as you’re making and writing about
> them, I’m pretty sure on both sides of the border it’s spelled “axle”.
>
> Stay on top,
>
> John Foss, the Uni-Cyclone http://www.unicycling.com

Re: MUni hub design

Kris Holm wrote:

> Over the last few months I’ve been experimenting with a couple of different
> hub designs, to try to design an extremely strong hub capable of with standing
> huge drops. Thus far the most success I’ve had is with having a solid hub
> machined (turned on a lathe) out of a 3.5" diameter solid rod of 4140 steel
> (so the flanges are one-piece with the rest of the hub- no welding or
> press-fitting). I took a Fishbone “Big Ass” crankset, which consists of huge
> tubular 175 cm cranks, and a 20 mm thick 8 spline bottom bracket axel (22 mm
> outside the splines), cut the axel in half and welded the stubs into holes
> drilled in the end of the hub.
>
> The last one made this way lasted for about 1.5 months before the axel twisted
> and the weld broke when going off a big drop. Partly it failed due to improper
> heat treatment after welding.
>
> I’m building another similar one just so I can ride ASAP, but I had an idea I
> wanted to throw out:
>
> 1) Turn a similar hub on a lathe.
>
> 2) Have a gearmaker spline a long section of rod to match the spline pattern
> on the cranks, and have them also machine a keyway (square groove) between
> one of the splines (or miss a spline if necessary to make room for the
> keyway. Chop the long section into appropriate lengths, so you have lots of
> spares. Make this out of a super strong alloy like 3312 steel.

I would agree up to this point, splines are great, key ways are notorious for
producing stress raisers. Rather than a square or rectangular key a round key
has better properties but is considerably harder to produce. The other point
about keys is that when calculating the strength of a shaft you have to go to
the narrowest point which is the bottom of the key way shaft. On hubs the
diameter is where we are really pushing it and do not want to reduce the
theoretical diameter by putting a key or 5/8" tapers. I assume you are pressing
the bearing onto the spline. Again not ideal as there will be increased stresses
at the points of contact between the spline and shaft. It would be better if the
spline was ended gently before the bearing surface with gentle radii to reduce
any stress raisers. Sorry to be a bit negative but if we are going for the
ultimate…

Here is my 10c worth:

Start with a standard shaft/cranks, your suggestion of the Fishbone BMX 3 piece
crankset (175 mm cranks, 20 mm diameter 4130 CrMo bottom bracket axle) sounds
great. It is similar to what I was intending to start with although I measured
it as 19.05 (3/4") not 20 mm and have been able to get a set of 165 mm cranks
for it. ( I must go and check it again). I would then make the flanges in 2
halves (L shape if you took a section through) also in CrMo so you can match the
welding wire exactly and you don’t have to use dissimilar welding techniques.
These I would machine to be a press fit over the shaft and press them on so that
the legs of the L are facing towards the centre. I would press the 2 sides in
until the flanges are in the desired position and there is about 25 mm in the
centre. Then weld the flanges to the shaft in the centre only - not on the
outside! The whole unit will then need heat treating again to return it to it’s
original strength as 4130 anneals when welding. Here is my reasoning: Rigid
systems always fail, you should always allow for some flex even in a material
like CrMo that is incredibly stiff it will want to twist. By transferring the
load over a larger proportion of the shaft the load is less concentrated, hence
less likely to fail.

Hope this helps

Cheers

Roger

Re: MUni hub design

Each rider individually puts no more weight on their cranks and bottom bracket
than on a regular mountain bike. Sure, the wheel hubs are stronger but since the
axel inside the crank arm is usually the limiting factor, I think that BMX type
splined systems are the way to go.

At 06:54 AM 3/25/99 GMT, you wrote:
>Out of curiousity, wouldn’t the hubs or hub shells made for MTB tandems have
>sufficent strength? Since they’re designed to support two riders they should be
>good enough for a single rider MUni. Or am I missing something? Jim
>
>Foss, JohnX wrote:
>>
>> > Anybody have any comments about this design idea?
>>
>> I think turning the hub from a single block of steel is overkill. I’ve
never
>> seen the flanges fail. In my experience, unicycle hubs always break between
>> the bearing and the crank. I believe the one you had last fall at MUni
>> Weekend may have failed in a different way, but it was built differently from
>> common unicycle hubs, I think.
>>
>> I would imagine that hub flanges could be welded onto whatever kind of axle
>> you can make out of indestructible stuff. After watching Trials experts at
>> the Sea Otter Classic on Sunday, I’ve seen what they do/use and we must be
>> able to make something similar for us.
>>
>> Can hub flanges be welded onto a high-end trials crankset?
>>
>> BTW, I hate to bring this up, but as long as you’re making and writing
about
>> them, I’m pretty sure on both sides of the border it’s spelled “axle”.
>>
>> Stay on top,
>>
>> John Foss, the Uni-Cyclone http://www.unicycling.com
>


Kris Holm, B.Sc. Geologist, Forestry Group, EBA Engineering Consultants Ltd.
Suite 550, Sun Life Plaza, 1100 Melville Street, Vancouver, B.C. V6E 4A6
Tel:(604) 685-0275 Fax:(604) 684-6241 Email: kholm@eba.ca

RE: MUni hub design

>I think turning the hub from a single block of steel is overkill.

I would disagree. Making a one piece hub is highly advantageous. I have had an
axle fail at the inside of the flange weld. This is presumably due to the weld
heat stress on the steal. Granted, it was probably not properly heat treated,
but nonetheless, any welding invariable weakens the piece. I have been told that
it could be cost effective to make a single unit axle in small quantities.
Making straight flanges on a single piece axle would not be difficult. But the
flanges need to be angled to match the angle of the spoke. I don’t know much
about machining, but I can’t imagine that it would be real easy to machine a
flange with a very slight inward angle. From what I’ve picked up, the flange
angle and the axle splinning would be the most challenging parts of the axle.

>Can hub flanges be welded onto a high-end trials crankset?
Depends on the crankset. The standard bearing-cone crankset cannot easily be
welded to. The cone is tapered to hold the bearing cage in frame. So there isn’t
a flat area on the axle to weld flanges to. But, high end BMX bikes use cased
bearings. The axle is flat and the bearings are press fit onto the axle similar
to unicycles. I think the one I saw was 1/2 inch high quality chrome-molly. It
would be very easy to weld to an axle such as this. The problem, as usual, is
that only 175mm matching spline cranks are available for this axle.

Brett Bymaster http://shay.ecn.purdue.edu/~bymaster bymaster@purdue.edu

At 08:31 AM 3/24/99 -0800, you wrote:
>> Anybody have any comments about this design idea?
>
>I think turning the hub from a single block of steel is overkill. I’ve never
>seen the flanges fail. In my experience, unicycle hubs always break between the
>bearing and the crank. I believe the one you had last fall at MUni Weekend may
>have failed in a different way, but it was built differently from common
>unicycle hubs, I think.
>
>I would imagine that hub flanges could be welded onto whatever kind of axle you
>can make out of indestructible stuff. After watching Trials experts at the Sea
>Otter Classic on Sunday, I’ve seen what they do/use and we must be able to make
>something similar for us.
>
>Can hub flanges be welded onto a high-end trials crankset?
>
>BTW, I hate to bring this up, but as long as you’re making and writing about
>them, I’m pretty sure on both sides of the border it’s spelled “axle”.
>
>Stay on top,
>
>John Foss, the Uni-Cyclone http://www.unicycling.com
>

RE: MUni hub design

Okay, Okay, I always seem to spell axle wrong!

The reason for the one-piece axel (just joking- axle) was logistics. A friend
has access to a good metal lathe, but doesn’t know how to weld, so it was less
expensive, if more time consuming, to make a one-piece design.

“Trials experts” break stuff all the time and have similar problems to MUni- the
Norco Factory Trials Team has designed and is designing custom stuff for
themselves because they break stock components. North Shore (technical downhill)
riders here in Vancouver also break tons of stuff; I’ve been on lots of rides
where at least one person breaks a bottom bracket. Talking to Race-Face Cranks
Ltd. in Vancouver, they said that the bottom bracket designs on standard bikes
are on the small side for hardcore use, but that they are forced to design
cranksets for this size because it is simply that, a standard size.

Since MUni is much harder on axles than bikes, especially than full-suspension
bikes, I really think that a replaceable axle is a good idea.

At 08:31 AM 3/24/99 -0800, you wrote:
>> Anybody have any comments about this design idea?
>
>I think turning the hub from a single block of steel is overkill. I’ve never
>seen the flanges fail. In my experience, unicycle hubs always break between the
>bearing and the crank. I believe the one you had last fall at MUni Weekend may
>have failed in a different way, but it was built differently from common
>unicycle hubs, I think.
>
>I would imagine that hub flanges could be welded onto whatever kind of axle you
>can make out of indestructible stuff. After watching Trials experts at the Sea
>Otter Classic on Sunday, I’ve seen what they do/use and we must be able to make
>something similar for us.
>
>Can hub flanges be welded onto a high-end trials crankset?
>
>BTW, I hate to bring this up, but as long as you’re making and writing about
>them, I’m pretty sure on both sides of the border it’s spelled “axle”.
>
>Stay on top,
>
>John Foss, the Uni-Cyclone http://www.unicycling.com
>


Kris Holm, B.Sc. Geologist, Forestry Group, EBA Engineering Consultants Ltd.
Suite 550, Sun Life Plaza, 1100 Melville Street, Vancouver, B.C. V6E 4A6
Tel:(604) 685-0275 Fax:(604) 684-6241 Email: kholm@eba.ca

Re: MUni hub design

A while back I heard that Phil Wood, who’s company makes MTB hubs and other
items, made some proto-type unicycle hubs. He was looking for a company that
produces unicycles to see if there is enough interest.

If he has enough interest to have made a prototype, then maybe he would be
interested enough to deal with the issues surrounding producing a hub strong
enough for riding off road. -Mary

Brett Bymaster <bymaster@purdue.edu> wrote in article
<3…5.32.19990324171512.00909ce0@purdue.edu>…
>
> >I think turning the hub from a single block of steel is overkill.
>
> I would disagree. Making a one piece hub is highly advantageous. I have had an
> axle fail at the inside of the flange weld. This is presumably
due
> to the weld heat stress on the steal. Granted, it was probably not properly
> heat treated, but nonetheless, any welding invariable weakens
the
> piece. I have been told that it could be cost effective to make a single unit
> axle in small quantities.
>
>
> Brett Bymaster http://shay.ecn.purdue.edu/~bymaster bymaster@purdue.edu
>
>
> At 08:31 AM 3/24/99 -0800, you wrote:
> >> Anybody have any comments about this design idea?
>

Re: MUni hub design

Kris, you are a true wildman. My only comment is that I hope you will bring all
of these designs to NUC this summer so we can see them.

—Nathan

Kris Holm wrote in message
<3..3.32.19990325194827.006bca80@199.185.15.66>…
>I just talked to a machinist last night and I decided to go ahead with an an
>axle design that hopefully might be a decent compromise between high strength
>and logistics.

[etc]

RE: MUni hub design

I just talked to a machinist last night and I decided to go ahead with an an
axle design that hopefully might be a decent compromise between high strength
and logistics.

He’s going to take a Fishbone BMX 3-piece crankset (175mm cranks, 20mm diam 4130
CrMo bottom bracket axle), and cut the axel in half. Each stub will be inserted
into holes drilled in a 4140 one-piece steel hub. He will drill a tapered hole
through just inside the flange, so that it goes through both the hub and the
axle (1/4"thick where it goes through the axel). A tapered pin will be driven
into this hole. The top of the hole will be tapped to accept a set-screw, which
will hold the taper pin in place. A very small diameter hole will be drilled
from the bottom of the taper hole through to the other side of the hub. This
hole is so that you could punch the taper-pin out for axel replacement.

Both the axel and hub will then be heat-treated.

If properly machined to close-tolerances, the specs for the pin say that it will
hold over 5000 lbs of shear force. One question is, will the hole drilled in the
axle make the axel significantly weaker? Also, would shock loading produce more
force than 5000 lbs? I don’t know but I could hardly imagine that it could.

This system has the major advantage that, in addition to having replaceable
axles, it also requires only minor modification to a readily available crankset,
and no special tools are required to replace axels as long as you have had
spares made. However, I don’t think it is as strong as the keyway design. I
guess I’ll see whether it’s strong enough!

Any comments?

-Kris.

At 05:15 PM 3/24/99 -0800, you wrote:
>
>>I think turning the hub from a single block of steel is overkill.
>
>I would disagree. Making a one piece hub is highly advantageous. I have had an
>axle fail at the inside of the flange weld. This is presumably due to the weld
>heat stress on the steal. Granted, it was probably not properly heat treated,
>but nonetheless, any welding invariable weakens the piece. I have been told
>that it could be cost effective to make a single unit axle in small quantities.
>Making straight flanges on a single piece axle would not be difficult. But the
>flanges need to be angled to match the angle of the spoke. I don’t know much
>about machining, but I can’t imagine that it would be real easy to machine a
>flange with a very slight inward angle. From what I’ve picked up, the flange
>angle and the axle splinning would be the most challenging parts of the axle.
>
>>Can hub flanges be welded onto a high-end trials crankset?
>Depends on the crankset. The standard bearing-cone crankset cannot easily be
>welded to. The cone is tapered to hold the bearing cage in frame. So there
>isn’t a flat area on the axle to weld flanges to. But, high end BMX bikes use
>cased bearings. The axle is flat and the bearings are press fit onto the axle
>similar to unicycles. I think the one I saw was 1/2 inch high quality
>chrome-molly. It would be very easy to weld to an axle such as this. The
>problem, as usual, is that only 175mm matching spline cranks are available for
>this axle.
>
> Brett Bymaster http://shay.ecn.purdue.edu/~bymaster bymaster@purdue.edu
>
>
>At 08:31 AM 3/24/99 -0800, you wrote:
>>> Anybody have any comments about this design idea?
>>
>>I think turning the hub from a single block of steel is overkill. I’ve never
>>seen the flanges fail. In my experience, unicycle hubs always break between
>>the bearing and the crank. I believe the one you had last fall at MUni Weekend
>>may have failed in a different way, but it was built differently from common
>>unicycle hubs, I think.
>>
>>I would imagine that hub flanges could be welded onto whatever kind of axle
>>you can make out of indestructible stuff. After watching Trials experts at the
>>Sea Otter Classic on Sunday, I’ve seen what they do/use and we must be able to
>>make something similar for us.
>>
>>Can hub flanges be welded onto a high-end trials crankset?
>>
>>BTW, I hate to bring this up, but as long as you’re making and writing about
>>them, I’m pretty sure on both sides of the border it’s spelled “axle”.
>>
>>Stay on top,
>>
>>John Foss, the Uni-Cyclone http://www.unicycling.com
>>
>>
>


Kris Holm, B.Sc. Geologist, Forestry Group, EBA Engineering Consultants Ltd.
Suite 550, Sun Life Plaza, 1100 Melville Street, Vancouver, B.C. V6E 4A6
Tel:(604) 685-0275 Fax:(604) 684-6241 Email: kholm@eba.ca