[Surly]

Hey guys--I'm looking to build my own telescoping seat post. I was going to pick up and Axiom, but the reviews all mention what poor quality the build is.
Anybody have tips or things I should look out for?

MY seat tube is 30.9 so I figured I'd find an aluminum post to fit, and replace th seatclamp w/ a QR collar. Do I need to do much besides machine a "V" do the QR will tighten?

Once that was done, I figured I'd find a carbon or another aluminum post that was smaller than the ID of the outer post.

Any thoughts? Anybody else try this?
Thanks!

 

[Rik]

One word: overlap!

and a few more words:
Sounds like an interesting project, make sure you test and test before you actually ride the thing, because that area of your body doesn't like sharp jagged aluminium at all
You may well be able to get the right size seatposts from a shop, I'd say use a 25.4 seatpost for the inner one, maybe even a steel bmx post, for the extra strength you'll need. Just an idea though.

 

[Surly]

Thanks for the tips--any suggestions on testing?

I have little experience w/ machine shops--if I call one up, can I just ask for cro-mo tubing w/ a ED of 30.9 and and ID of 25.4?

Thanks!

 

[ohio]

Originally posted by Surly
can I just ask for cro-mo tubing w/ a ED of 30.9 and and ID of 25.4?

Thanks!

You probably won't find it. that's an odd outer size (inner size is 1"). Even if you did. you wouldn't want steel. At that thickness it'll weigh about 4 lbs, and will be super overkill. I'd get some aluminum with the 25.4 inner, have it turned down to a 30.9 outer and have the slot in the back machined in at the same time. Don't just cut the slot with a saw and DON'T cut a V-notch... if it's not a slot with a round end it will devolop cracks and break. For the inner you can go with steel if you feel the need, but at that diameter you don't need it for the outer.

 

[Surly]

Fantastic advice-- any suggestions on a grade of aluminum, and where I might be able to find a small amount? Foes and Chumba Wumba are both within driving distance--do ya think they might have a bit of tubing to sell?
Once I find the aluminum, should I try to get the stuff heat treated?

thanks!

 

[ohio]

Originally posted by Surly
Fantastic advice-- any suggestions on a grade of aluminum, and where I might be able to find a small amount?
Once I find the aluminum, should I try to get the stuff heat treated?

thanks!

Check the yellow pages a local machine shop or metal supplier. You're basically looking for a scrap so it should be cheap or free.

Since you don't have to weld it, don't worry about heat-treating. Extruded tubes come with a heat-treat already, and you won't need to treat them again unless they get welded. Also, since you don't have to weld, you can use a stronger grade if you can find them. If you can get ahold of 7075, that's strong stuff. So is 2024.

But most shops won't have them lying around.

6061 T-6 or 7005 will both work if you can't find the others, and it's guaranteed the shop will have 6061 on hand.

 

[Surly]

Thanks for the help--I'll post pics when I get the materials together.

 

[Tusca]

an easy way to do it, maybe not cheaper is to just buy a cheap 30.9 seatpost, cut the clamp off it and file a slot, not a V.
you can get 30.9 seat qr's easy enough. then all you have to do is
buy whatever seatpost fits inside the sleeve you created.
the axiom telescopics are great but the clamp is not pressed in very well and comes loose easily.

for their 30.0 post, they use a 27.0 inner post and
for their 31.8 post, they use a 27.2 inner post.

i'm pretty sure a 27.2 will work just fine after you slaughter a 30.9 kalloy seatpost ($20) to make your sleeve.

i don't like the idea of 25.4 inner posts, that is not very big and non-standard.
once you make your own sleeve, it's not that hard to figure out what size post will fit into it and you will have a wide range of seatpost options. i replaced the inner post of my axiom with a thomson and it was perfect after that.

 

[Surly]

Interesting--my Giant has a seattube ID of 30.9, w/ a shim from 30.9-27.2 inside.


You're suggesting that I find a 30.9 post, cut the clamp, and put a collar and shim inside, and drop the post I'm already using into it?

I'll try it! Thanks!

 

[crashing_sux]

Why not get a power post instead. Few people remember them, I get tons of stares out on the trails. A company named Power Post made a seat post a few years back (also called a Power Post) that had a parallellogram linkage (people always think it's some sort of suspension post like a thudbuster) and was cable operated by a thumb lever on your handlebar. I found a guy who used to race for them and still had one in his garage and then had my local machine shop make me a larger seatpost for it (30.9mm) to fit my specialized enduro.

This is a very slick unit, when you hit the thumb lever you can sit down on the seat and it will drop down and back, very similar to the position you would put your body in if you didn't have a seat and were going down a steep hill, with the seat falling down over the rear tire. There is also a position I rarely use that fold the seat forward and down so that it lays directly on top of your top tube, it's like not even having a seat. I pretty much only use it for the gnarliest of terrain or while screwing around on jumps and stuff. It's really nice to hit a big downhill and drop the seat down and back over the rear tire as I'm blasting downhill and then at the bottom have it move back into the normal position for climbing again.l

- Shane

 

[riderx]

A source for tubing - not sure if it will be the grade you need - is www.McMaster.com

They also have all kinds of stuff for DIY projects of just about any type.