New Idea for Re-enforcing Seatposts

Well i dont kno about you but i dont have 20 different sized people
unsing my uni so my seat hieght never changes.

And because of the over lap that the second peice of seatpost would
have on the seatpost clamp it would be very unlikely that it would be
able to tip enough to break... However after i try this i will let you
all kno how it works.

--
trials_uni

TRIALS 4 LIFE !

Quoted message said:

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harper said:

Bruce-
Quick. Put me on e-Bay.

w00t...i got reply # 60666 in MR
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I second the idea of putting something -inside- the seatpost.

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onelesscar

mmm...i love my qu-ax...
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why not do the same thing but instead put a section of 22mm seatpost
inside a 27 mm seatpost?

I still dont think its a very good idea because although it would make
the tube stronger it would just move the stress up to where the post
connects to the plate.

Try it and tell us what happens.

Cheers,
Max

--
max_pfeifer

edsbelly said:

'I'm goin to ride down the street one day yelling and screaming 'oh dear
god, ive got half a bike stuck up my ass!!"

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I've seen a few post failures and they all seem to be connected to
failure of the mounting plate at the top of the post, rather than the
post itself, maybe the post itself isn't the thing to concentrate on
improving.

Your design is likely to concentrate the stress at the point where the
outer tubing stops, and will likely cause snapping of the inner post
just above the top of your frame. However, some interesting ideas stem
from yours, namely a seatpost that changes diametre, thin at one end to
fit in the frame, with a larger diametre but equal metal cross-section
at the other (i.e. thinner walls). This would weigh no more but the
increased diametre increases the second moment of inertia and thus
increases the beam yield force. But then i suppose if you're going to
all the trouble of that you may aswell just use a frame with a bigger
seatpost tube and use a large, thin wall tube.

You could try welding a flat flange down the front of the post, this
would make the post vastly more difficult to bend, it would certainly
move the failure point up to the seat mounting plate.

Random thought: why do we use circular posts to mount seats on? Bearing
in mind that the seat doesnt need to rotate, and the vast majority of
the force are front/back rather than left/right wouldn't an I-beam or
similar be better? It's far too tedious for me to work out right now,
does anyone know off-hand for an equal material cross-section (or mass
per length) whether tube or I-beam is stronger?

--
kington99

Dave

- what a thoroughly post-modern subversion of the cycling genre -
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kington99 said:

I've seen a few post failures and they all seem to be connected to
failure of the mounting plate at the top of the post, rather than the
post itself, maybe the post itself isn't the thing to concentrate on
improving.

Your design is likely to concentrate the stress at the point where the
outer tubing stops, and will likely cause snapping of the inner post
just above the top of your frame. However, some interesting ideas stem
from yours, namely a seatpost that changes diametre, thin at one end to
fit in the frame, with a larger diametre but equal metal cross-section
at the other (i.e. thinner walls). This would weigh no more but the
increased diametre increases the second moment of inertia and thus
increases the beam yield force. But then i suppose if you're going to
all the trouble of that you may aswell just use a frame with a bigger
seatpost tube and use a large, thin wall tube.

You could try welding a flat flange down the front of the post, this
would make the post vastly more difficult to bend, it would certainly
move the failure point up to the seat mounting plate.

Random thought: why do we use circular posts to mount seats on? Bearing
in mind that the seat doesnt need to rotate, and the vast majority of
the force are front/back rather than left/right wouldn't an I-beam or
similar be better? It's far too tedious for me to work out right now,
does anyone know off-hand for an equal material cross-section (or mass
per length) whether tube or I-beam is stronger?

what he said

--
max_pfeifer

edsbelly said:

'I'm goin to ride down the street one day yelling and screaming 'oh dear
god, ive got half a bike stuck up my ass!!"

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kington99 said:

I've seen a few post failures and they all seem to be connected to
failure of the mounting plate at the top of the post, rather than the
post itself, maybe the post itself isn't the thing to concentrate on
improving.

Your design is likely to concentrate the stress at the point where the
outer tubing stops, and will likely cause snapping of the inner post
just above the top of your frame. However, some interesting ideas stem
from yours, namely a seatpost that changes diametre, thin at one end to
fit in the frame, with a larger diametre but equal metal cross-section
at the other (i.e. thinner walls). This would weigh no more but the
increased diametre increases the second moment of inertia and thus
increases the beam yield force. But then i suppose if you're going to
all the trouble of that you may aswell just use a frame with a bigger
seatpost tube and use a large, thin wall tube.

You could try welding a flat flange down the front of the post, this
would make the post vastly more difficult to bend, it would certainly
move the failure point up to the seat mounting plate.

Random thought: why do we use circular posts to mount seats on? Bearing
in mind that the seat doesnt need to rotate, and the vast majority of
the force are front/back rather than left/right wouldn't an I-beam or
similar be better? It's far too tedious for me to work out right now,
does anyone know off-hand for an equal material cross-section (or mass
per length) whether tube or I-beam is stronger?

isn't a hollow cylinder the best weight-strength or thickness/strength
ratio... so that said the I beam would be weaker... but it is a good
idea 🙂
umm they could be made slightly oval or square or something too, im
probably not right tho cuz I didn't research it out or anything

hm... rectangular seatposts for christ?? whos starting that one? :p :p

--
skrobo

*><> Unicycle For Christ <>< PM me if you would like to
join!!!*
ok i have been riding for 3 years, doing tricks for 6 months and being
sorta hardcore for 3 months (before that the only trick i did was a
hop-180 to backwards riding or a spin off of a wall or something

-stephen-
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Okay, next custom uni someone builds has to have a -square- seatpost and
tell us how it works.

--
onelesscar

mmm...i love my qu-ax...
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kington99 said:

Random thought: why do we use circular posts to mount seats on? Bearing
in mind that the seat doesnt need to rotate, and the vast majority of
the force are front/back rather than left/right wouldn't an I-beam or
similar be better? It's far too tedious for me to work out right now,
does anyone know off-hand for an equal material cross-section (or mass
per length) whether tube or I-beam is stronger?

I think an I-Beam seat post would likely fail becuse of torque. I mean
with a standard seat post it if's just a little bit loose, it often
gets turned a little bit whole riding, which certainly indicted that
some torqe forces are applied to the post during riding especailly in
turning.

--
ThisGuyIKnow
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the problem with seat posts is the way they are made.

as welding is very weak and it can be subject to a lot of stress and
therefore end up breaking.

the manufacturers need to start making them by casting. this is not
very possible unless you have a workshop but even then it is not easy.
if you were to make a one off, it can be done by sand casting.

therefore it is unlikely that many of you will be able to do it at
home.

this way of making the seatpost would take much longer so it would be
much more expensive but also a lot stronger if done properly, as there
is no welding that is needed to be done.

so if any of you own a unicycle making factory or work in one you could
suggest this idea

--
will--hare
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I actually have my seatpost reinforced right now, I guess this would
work for pretty much anyone, and it's really simple to do too.

I had a lot of problems with the little tab on top of the seatpost
bending, when I landed on the front bit of my seat. The tab would bend
down, and the seatpost would be ruined. So I came up with this clever
idea, to weld a little piece of metal in between the tab and the
seatpost. This will also stop any breakage due to pulling hard on the
seat or anything, and will also stop ripping of the area between the
tab and the seatpost.

Unfortunatly, the unicyclist.com gallery is not exactly cooperating, so
the illustration will have to wait for a bit.

--
Erant

*"There is power in your wall sockets, too, but I don't recommend that
you plug yourself in to learn a 540 unispin."* - Harper
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What a silly idea...

--
DustinSchaap

Sponsored by 'MUNICYCLE.COM' (http://municycle.com) and 'SEMCYCLE'
(http://semcycle.nl)

(old nick: dustinmichels)
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[image:
http://www.unicyclist.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=221740&g2_serialNumber=1&g2_GALLERYSID=e200519cdf46d06fd8e7186f04c23fd9]

--
Erant

*"There is power in your wall sockets, too, but I don't recommend that
you plug yourself in to learn a 540 unispin."* - Harper
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Erant has invented the gusset. Just as I did in the early 90s. The
engineering concept behind it is quite old, but it seems the simplest
way to keep your seatpost from breaking. I have many different
seatposts that have been reinforced in that manner.

Is anyone out there having problems with seat posts that don't involve
the plate where it connects to the seat? That's the part that needs
reinforcing, the tube is usually fine. Today's stronger, stiffer seats,
and the type of riding we do now with lots of seat yanking, both are
causes of more seatpost problems than in the past.

--
johnfoss

John Foss
"jfoss" at "unicycling.com" -- www.unicycling.com
-----------------------------------------------

"The worst thing you can do on a unicycle when you land is stop dead."
-- Kris Holm, world's expert on high-consequence unicycling
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johnfoss said:

But it seems the simplest way to keep your seatpost from breaking.

It is, I've thought up quite a few different things, but this was the
only that thing that was easy to fabricate, and easy to install. That
is, for anyone that has access to a MIG welder. I originally intended
to build one that is removable, just in case I do break a seatpost, but
never needed it. Been riding on this reinforced seatpost for about 6
months now, no breakage.

--
Erant

*"There is power in your wall sockets, too, but I don't recommend that
you plug yourself in to learn a 540 unispin."* - Harper
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