Swing arm bearing

Green Gear - Bike Friday has lots of experience

"JT" <[email hidden]> wrote in message
"]news:[email hidden]...
| I want to put a swing arm onto a bike I'm building, but
| what bushing,
what's
| the best aproach?
|
| Any know-how out there would be much appreciated.
|
| Regards JT
|
|

Depending on the weight of the rider(s) and how hard you
intend to use it, my friends and I use 1/2"(or 12mm) or 3/8"
precision bearings and a grade 8 pivot bolt. Make/get a
piece of steel tube and press the bearings into the end with
a compression tube in the middle. The 1/2" & 12mm would be
for the heavier/harder rider while the 3/8" would be for
lighter and more moderate riders (say 210lbs and under ?).

"JT" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I want to put a swing arm onto a bike I'm building, but
what bushing,

what's

Quoted message said:

the best aproach?

Any know-how out there would be much appreciated.

Regards JT

"Sticker Jim" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Depending on the weight of the rider(s) and how hard you
intend to use it, my friends and I use 1/2"(or 12mm) or
3/8" precision bearings and a grade

8

Quoted message said:

pivot bolt.

Here's one vote that says precision bearings and Grade 8 are
vast overkill/expense.

First, figure that the suspension spring/damper element
itself has stiction/viscous friction to begin with (some
commercial suspension elements have a LOT of striction), so
trying to minimize it at the swing arm pivot joint is
pointless.

Second, figure the loads. Rider and vehicle weight are
largely supported by the spring/damper, and the direct
radial loads on the bearings derive primarily from
traction and braking, which is to say they are not that
great. The significant loads on a swing arm derive from
the side loads from wind and cornering. Though the
external forces may be modest, they are applied over lever
arms the size of ,say, the wheel radius or the swing arm
length, and the resulting moments must be taken out across
the side-to-side span of the pivot joint. Notice that
these loads in a trike swing axle pivot might be 5 or 10
times those generated in a two-wheeler. These applied
moments are related to the other critical design issue,
wheel alignment, which I'll discuss below.

Third, consider the application. Ball bearings are designed
and built to spin, and they're not particularly happy making
small reciprocating motions as in a suspension joint. Now,
in this case the loads are low, and I'm not claiming that
they'll fail, but they're overkill. Look around at
production automotive applications - a world of 100,000 mile
warrantys and micro-penny counting. I can't think of a place
where ball or roller bearings are used like that. Where low
friction reciprocating joints are required, you sometimes
see needle bearings, where the displacement allows for a
turn or two of the rolling element.

Fourth, alignment. Fore and aft alignment is not important,
side-to-side medium important. What is critical are the
wheel alignments: 1.) toe (angular displacement of the rear
wheel about a vertical axis), and 2.) camber (angular
displacement of the rear wheel about the longitudinal axis
of the vehicle.), both relative to the position of the front
wheel. These alignments are established by the relative
positions of the two swing arm pivot bearings. Initial
misalignment, structural flexibility, excessive clearances,
or wear here will kill the design.

So, considering all of this, what does the bearing look
like? Considering the small motions, it'll have a bushing
(well-greased bronze or Delrin if the loads are right)
running in a thin-wall housing on a thin wall largish
diameter shaft. The downside here is the weld or braze
distortion you get when you join the housing to the frame.
If you have a shop, it's pretty straightforward to bore the
housing after welding, hard without the shop.

But the really nifty solution would be to rip the design off
race cars. Use a pair of spherical joints threaded into the
ends of the swing arms. Compute the load ranges and pick a
ball joint technology (bronze, Delrin, etc.) that fits. Make
the span of the joint wide enough to get the loads and the
alignment sensitivity down.

If you're building with angle-iron-hack-saw-and-stick-
welder, you can use four or five spherical joints and
forget about alignment altogether until you get to the
mechanical assembly.

Use bolts soft enough to drill out the centers. When you
size the ball joint for load, you won't need anything like
the full bolt area for shear. Before hitech materials
arrived, it was common for race car designers to drill out
bolt centers to save weight. It's a little mysterious why
this technique hasn't percolated down into recumbents.

Too, it baffles me why people insist that Grade 8 bolts are
the "best" for anything. For moving vehicles "best" is
usually AN.

Just free advice, Fred Klingener

"Fred Klingener" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

"Sticker Jim" <[email hidden]> wrote in message news:MY6xc.1-
[email hidden]...

Quoted message said:

Depending on the weight of the rider(s) and how hard you
intend to use

it,

Quoted message said:

Quoted message said:

my friends and I use 1/2"(or 12mm) or 3/8" precision
bearings and a

grade

Quoted message said:

8

Quoted message said:

pivot bolt.

Here's one vote that says precision bearings and Grade 8
are vast overkill/expense.

First, figure that the suspension spring/damper element
itself has stiction/viscous friction to begin with (some
commercial suspension

elements

Quoted message said:

have a LOT of striction), so trying to minimize it at the
swing arm pivot joint is pointless.

Second, figure the loads. Rider and vehicle weight are
largely supported

by

Quoted message said:

the spring/damper, and the direct radial loads on the
bearings derive primarily from traction and braking, which
is to say they are not that great. The significant loads
on a swing arm derive from the side loads from wind and
cornering. Though the external forces may be modest, they

are

Quoted message said:

applied over lever arms the size of ,say, the wheel radius
or the swing

arm

Quoted message said:

length, and the resulting moments must be taken out
across the

side-to-side

Quoted message said:

span of the pivot joint. Notice that these loads in a
trike swing axle pivot might be 5 or 10 times those
generated in a two-wheeler. These applied moments are
related to the other critical design issue, wheel
alignment, which I'll discuss below.

Third, consider the application. Ball bearings are
designed and built to spin, and they're not particularly
happy making small reciprocating

motions

Quoted message said:

as in a suspension joint. Now, in this case the loads are
low, and I'm

not

Quoted message said:

claiming that they'll fail, but they're overkill. Look
around at

production

Quoted message said:

automotive applications - a world of 100,000 mile
warrantys and

micro-penny

Quoted message said:

counting. I can't think of a place where ball or roller
bearings are used like that. Where low friction
reciprocating joints are required, you sometimes see
needle bearings, where the displacement allows for a turn
or two of the rolling element.

Fourth, alignment. Fore and aft alignment is not
important, side-to-side medium important. What is critical
are the wheel alignments: 1.) toe (angular displacement of
the rear wheel about a vertical axis), and 2.) camber
(angular displacement of the rear wheel about the
longitudinal axis of the vehicle.), both relative to the
position of the front wheel. These alignments are
established by the relative positions of the two swing arm
pivot bearings. Initial misalignment, structural
flexibility, excessive clearances, or wear here will kill
the design.

So, considering all of this, what does the bearing look
like? Considering the small motions, it'll have a bushing
(well-greased bronze or Delrin if the loads are right)
running in a thin-wall housing on a thin wall largish
diameter shaft. The downside here is the weld or braze
distortion you get when you join the housing to the frame.
If you have a shop, it's pretty straightforward to bore
the housing after welding, hard without the shop.

But the really nifty solution would be to rip the design
off race cars.

Use

Quoted message said:

a pair of spherical joints threaded into the ends of the
swing arms. Compute the load ranges and pick a ball joint
technology (bronze, Delrin, etc.) that fits. Make the span
of the joint wide enough to get the loads and the
alignment sensitivity down.

If you're building with angle-iron-hack-saw-and-stick-
welder, you can use four or five spherical joints and
forget about alignment altogether until you get to the
mechanical assembly.

Use bolts soft enough to drill out the centers. When you
size the ball joint for load, you won't need anything like
the full bolt area for shear. Before hitech materials
arrived, it was common for race car designers to drill out
bolt centers to save weight. It's a little mysterious why
this technique hasn't percolated down into recumbents.

Too, it baffles me why people insist that Grade 8 bolts
are the "best" for anything. For moving vehicles "best" is
usually AN.

Just free advice, Fred Klingener

Good points, but . . .

First, I'm not an engineer. I try to take into consideration
the direction of the loads but I have no idea what the loads
are, nor do I know what the bearings, bolts, steel, etc
loads are. What I do know about is rider abuse. I usually
try to idiot-proof anything I build but I am sometimes
surprised.

I understand what role the bearings play and what they are
designed for but for lack of anything better/more applicable
at the same price, I use the bearings. They have precision
dimensions, fit easily in standard tubing (no machining),
they're hardened and easy to come by. Sintered bushings are
easy to get and cheap but also much softer. I've seen guys
that used bushings for similar pivot points and they get
elongated in the small section where they are constantly
under load and that doesn't include the wrenching/yawing
motion that the lateral forces from a trike would add.

I get precision bearings at a pretty good price (I think) of
about $2.50 Cdn ea - that's $5 for two 12mm or 1/2" bearings
- 3/8" are less. A grade 8 bolt is less than $2 and a Gr 5
is cheaper still. They have more than enough strength BUT
I'm interested in hardness, not shear or tensile str. I've
seen and had stainless and Gr 2 bolts bend and shear (even
Gr 5 bolts), especially on chain pulleys when someone gets
on and tries to power away in high gear. So, for ~$12 I have
a pretty sweet pivot point not counting maybe another $1 in
washers and a nyloc nut. No slop, and no play in this
assembly either.

Now, let's switch to your idea of the spherical type rod
end. The cheapest ones I can get are $13 Cdn and I don't
really like them because there is already play in them.
That's for 5/16" too. If I get 3/8" and up it's over $15
each and that is for what I perceive to be low end rod ends.
They aren't stainless and don't have any kind of protective
boot. I have no idea how strong they are either (even the
parts store doesn't know/can't be bothered to find out). So,
I'm at $30 already and haven't bought any nuts, bolts or
washers AND I don't trust the joint already. I have no idea
what good joints would cost and the time it would take to
track them down would be more time than it would take to
build a pivot the way I do now. Also, all the current parts
I use were found at the same place I buy the rest of my
hardware so there was no searching required for them.

In the end, I'll buy a Gr 8 bolt and spend an extra .50
cents to a dollar on it because it's peace of mind. The
precision bearings are the same, AND cheap and easy to
replace (but I haven't heard of any of my friends needing to
replace theirs yet and that's with almost 2 years running
them at ~200 to 400 km a week. Good enough for me.

Reliable, inexpensive, TIGHT pivots are what is stopping me
from building a full suspension trike. I've seen some
commercial offerings of full suspension and even brand new,
there's play in them, too much for me to be happy with.

Lastly, while I am not much of a sheep, I am a little
pragmatic when it comes to pivot point design. Of all the
bikes and trikes I've seen with rear suspension, none of
them use spherical ball. I'm sure there's a reason why, but
I'm not wasting my time finding out because I'll be busy
building pivots the way I do. As I become 100% confident in
the strength, reliability and durability of the pivots, I'll
start downsizing components (which the 3/8" bolt is an
example) and again, I'll watch it 'til I'm happy with it. It
would be pretty easy to tear apart a commercial offering of
a pivot point and measure everything, but I don't have one
and don't know of anyone that would let me temporarily
disassemble theirs. I'm not too worried though as from the
looks of them, I decided to start with a bolt and 2
bearings, and go from there. In the end, the experimentation
and overbuilding only amounts to a few dollars per trike.
I'm fine with that. I'd rather be overbuilt/overkilled than
have it fall apart.

YMMV