Titanium Tube for a Seatpost

Unicycles and Equipment
1

Okay, material experts, speak up!

I’ve been offered a titanium pipe to make a seatpost with. It’s 27.2mm in diameter, but the walls are 0.9mm. Is that enough or would it be too weak? I’ve no experience with titanium whatsoever, so I don’t know.

I ride trials and street, quite aggressively sometimes and I’m only getting worse(as in more aggressive). I’ve broken one steel stock quax seatpost in the past, but now I have a 19" wheel and a carbon fibre base, so it will be even harder on the seatpost than before.

So, would it hold or not?

2

i think it would be close enough to be worth a try, the real question is where are you going to get a titanium plate to attach it to the seat, and how are you going to get the two welded together?

3

I’m gonna use the steel plate from my old broken seatpost.

An engineer friend of mine said he’d stick them together. I don’t remember how, I think weld them. But he knows what he’s talking about.

Edit: it’s just that I want it to be strong if I’m gonna ask him to put work into it, if you know what I mean.

What’s the normal thickness of steel seatpost walls? Aluminium?

4

I just took my seatpost off my MUni and measured the thickness with a ruler. It’s a knurled CroMo seat-post and looks to be slightly thinner than 2mm, around 1.8-1.9

5

Err… you’re going to stick a steel plate onto a titanium tube?

I’m getting the impression that just because it’s a titanium tube, you’re thinking that it’s going to make a super strong seatpost? For that to happen, I believe the bare minimum would be to have a fully titanium seatpost with quality welding.

I doubt steel and ti can be welded together, but I’m not 100% on that. Different alloys of ti can not even be welded together though… that’s the thing.

6

I don’t think it’ll be super-storng, but hopefully it’ll be lighter than the steel seatpost that I’ve got now. And anyway, it’s a good experiment to do.

I’ll post pictures and explanations of how it was done when we do it.

7

Use a Thomson seatpost and have your engineer friend make an adapter plate similar to this that would fit the Thomson post.

8

Sheer genius!

9

Titanium cannot be fusion welded to stainless steel but it can be vacuum brazed. This requires some specialized equipment but maybe your buddy has this. The 0.9mm wall thickness for titanium over the 27.2mm diameter will be plenty for strength. The weak point will be the joint. Maybe that doesn’t matter to you because you just want a titanium seat post because it would be cool. If we ride unicycles, who really cares about practical anyway?

10

^^^^^^^^^^^
Is that you Jerrick?

Or is it Harper having fun?

I’m confused?

11

haha.

So the thing is that I had warned Ivan there could be problems with this kind of post. We do not risk to make MTB seat posts out of these tubes because there is a chance of bending.

If Ivan was a light Danish girl, then it would be fine…:slight_smile:

12

Hmm, I’m more afraid that it would get damaged when I drop it on rocks doing trials and stuff like that, because of thin walls. I doubt I’d actually bend it. Maybe from sideways wwing or a messed up crankflip… But I’m mostly SIF.

And all light Danish girls are more than welcome to ride my uni. I’m really out of practice with my Danish dancing, gotta catch up, but I need a partner.

reprah: yes, I want a titanium seatpost purely for the jaw dropping effect that it inflicts on old ladies as I ride by. You hear them scream: “Is that the OT4 alloy?! Ummm, nama, narayana!!!” Gotta love it.

I think I’ll talk to the engineer about that adaptor. Seems like the best option, actually.

13

If you make the Ti post I’d put reinforcements, similar to the Qu-Ax post, but front and back.

14

Me and Dmitry have already had that idea, would be nice to materialize it :roll_eyes:

15

why front and back…do you ever break your seatpost on the backside?

16

:stuck_out_tongue:
I bet I couldn’t break the cheapest post out there. I have a lightweight post that flexes a lot, but nothing damaging. I have paralysis in my lower legs, braces are the only reason I was able to learn at all (see avatar).

One guy’s reinforced Al Qu-Ax post is already cracking at the joints. If it were reinforced front and back, those people who ride really hard can have a post that is reasonably priced and light w/o having to regularly replace it.

17

In that case I’d just give up on the whole idea. I really don’t like the qu-ax reinforced seatpost. Reinforcements on both sides would be just awful both for grip and looks.

18

Fixed it.

19

Hmm, I don’t think the reinforcements would get in the way. For unispins and sif I always hold my hands on the very outside of the seat with my fingers around the lip, it doesn’t seem like they would get close to the reinforcement. I haven’t used one before though so I can’t say for sure.

20

JC, I compared the top clamp of a Thomson seatpost to the bolt spread of a KH saddle. Unfortunately, the KH bolt pattern interferes with the distance spread of the 2-bolts in the Thomson post, such that the two are incompatible. However, the Miyata saddle bolt pattern might be possible, as that is longer and wider than the KH pattern.