home made seatpost

molybdenum or aluminum. you have hard time finding a source that would
sell you such a small piece. i guess you search out manufacturers that
use the pipe and raid their trash. easier to get it from bike shop that
accumlates used parts from discarded bikes.

Cyclopath! - Keiron said:

Over the last few weeks i've had difficulty locating 23.4mm seatposts. I got
my hands on a short one which is fine for now but i'm thinking a couple
extra inches would be nice, ahem. What sort of pipe could i use in order to
make a seatpost? What alloy are setposts generally made of? Lastly,
regarding the length of the post; seatposts generally have a minimum
insertion mark. is this usually determined by the length of the post and its
material or the pressure it creates on the frame?

thanks

Cyclopath! - Keiron said:

Over the last few weeks i've had difficulty locating 23.4mm seatposts. I got
my hands on a short one which is fine for now but i'm thinking a couple
extra inches would be nice, ahem. What sort of pipe could i use in order to
make a seatpost?

We did that for our tandem after we bent the original steel seatpost.
It uses a 25.0 mm diameter post and there were some pieces of 1"
diameter aluminum rod lying around so it was easy to just trim some
down by 0.4 mm. I had planned to drill out the inside to lighten it,
but that was taking awhile so we ended up just leaving it solid. I'm
sure it's the heaviest aluminum seatpost ever made but at least there's
no question about it being strong enough.

In article <[email hidden]>,

novice said:

molybdenum or aluminum. you have hard time finding a source that would
sell you such a small piece. i guess you search out manufacturers that
use the pipe and raid their trash. easier to get it from bike shop that
accumlates used parts from discarded bikes.

Agreed. When I was in the labs back at uni, for those small quantities,
we often just write to the manufacturers and given a good heart sobbing
story or cause. Invariably we'll get spared a small sample ample for
experiments. 🙂
--

Cyclopath! - Keiron said:

What alloy are setposts generally made of?

Ti 3Al 2.5V
Ti 6Al 4V
Aluminium 2024, 6061, 7075 and others
Aluminium Metal Matrix composite
Epoxy or Polyamide or Polypropylene matrix reinforced with glass,
carbon or aramid fibres or any mix of these
Steel from mild to CrMo and NiVaCr low alloy, also 18/8 and other
stainless steels.

I've had seatposts in most of the above materials over the years, all
within acceptable weight for application and none of them snapped off.
I've never seen magnesium alloys in this application, but if they're
good for stems they should be OK for seatposts too.

Tubes can be seamed or seamless drawn, or forged or molded or, I'm
guessing, sintered in the case of MMC, with separate head glued,
welded, screwed, pressed or riveted to the tube. One-piece units can
be forged, cast or machined from billet or a combination.

In other words, pretty much anything which comes to hand; I think you
could, at 23.4 OD solid, get away with oak or birch wood, and bamboo
is practically made for the job. Brass or bronze tube in the right
guage could work, and if you happened to trip over a length of nickel
or cobalt based alloy in the right size you could try that too. I'd
probably avoid depleted Uranium for home use due to toxicity and the
pyrophoric behaviour of the swarf, plus it's going to be heavy, and
Beryllium has similar problems albeit with an attractive weight.

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Cyclopath! - Keiron said:

What sort of pipe could i use in order to make a seatpost?

Aluminum, with a nice thick wall. The weight difference between "maybe
strong enough" and "definitely strong enough" is very small, so err on
the side of strength. 23.4mm = .921", which doesn't correspond to any
conventional tubing or pipe outside diameter, nor to any standard seat
guts interface. You'll have to turn the post to size on a lathe, or
else have somebody elsedo that for you. Fortunately, sizing a
modest-length plain seatpost is one of the simplest possible operations
that could be done on a lathe.

Wicks Aircraft sells metals by the foot. They offer a 1" aluminum
tubing with a 1/4" wall thickness that would work well for a 23.4mm
post with a 22.2mm top. That would give you a .188" wall thickness
where the saddle clamp mounts, and a .211" wall in the post itself--
plenty thick even for a small diameter post like that, (as long as it's
not overly long).

I have to observe that 23.4mm is a very strange post diameter. Is this
for an antique or homemade bike?

Quoted message said:

What alloy are setposts generally made of?

Most are 6061-T6 or equivalent. Some high-end posts are made of
2014-T3 or 7075-T6.

Quoted message said:

seatposts generally have a minimum
insertion mark. is this usually determined by the length of the post and its
material or the pressure it creates on the frame?

Both. But if you make a nice strong post, you will only have to ensure
that the lower end extends down past the seat tube/top tube/seat stay
joint.

Chalo

I said:

Wicks Aircraft sells metals by the foot. They offer a 1" aluminum
tubing with a 1/4" wall thickness that would work well for a 23.4mm
post with a 22.2mm top.

Here is the link:

http://www.wicksaircraft.com/catalog/product_cat.php/subid=1828/index.html

Chalo

Thanks all. will check with a few engineer friends at uni, they should be
able to help with what you suggest. Happy to know that atleast its feasible.
cheers

Cyclopath! - Keiron <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Over the last few weeks i've had difficulty locating 23.4mm seatposts. I

got

Quoted message said:

my hands on a short one which is fine for now but i'm thinking a couple
extra inches would be nice, ahem. What sort of pipe could i use in order

to

Quoted message said:

make a seatpost? What alloy are setposts generally made of? Lastly,
regarding the length of the post; seatposts generally have a minimum
insertion mark. is this usually determined by the length of the post and

its

Quoted message said:

material or the pressure it creates on the frame?

thanks

"Cyclopath! - Keiron" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Over the last few weeks i've had difficulty locating 23.4mm seatposts. I
got
my hands on a short one which is fine for now but i'm thinking a couple
extra inches would be nice, ahem. What sort of pipe could i use in order
to
make a seatpost? What alloy are setposts generally made of? Lastly,
regarding the length of the post; seatposts generally have a minimum
insertion mark. is this usually determined by the length of the post and
its
material or the pressure it creates on the frame?

thanks

Most any metal or wood would work. metal would be tubing hollow inside but
needs to be a reasonable thickness for the type of metal, Wood is usualy
solid.
I have seen guys using old broomstick or mop handles for seatposts before.
Once I had to use my lathe to machine a piece of aluminum rod stock to size
for a old oddball size seatpost, in order to make it longer. I basically
machined in a step so I could fit it inside the old seatpost in order to
make it longer. I used some epoxy like you use to glue golf club heads on
with. I also had to machine the diameter down a little bit as it wasn't a
normal sized seatpost.