DIY seatpost

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good idea/bad idea?

the seatpost head is for Cervelo frames, not sure of the insert diameter. a stainless steel tube with 2mm walls should be strong enough. I want to make a 24mm seatpost.

I could also shave .5mm off the walls of a kalloy 25mm. not sure how those forged heads are bonded, maybe its possible to remove with heat and reuse in a different post.

buy cheap large diameter seatpost and cut off the top with 50mm of post, bond that to tube inserted inside it. it might not look nice depending on the clamp design.

Ive a few other ideas, my goal is to have the cost below 40euro, ideally 20euro.

Could you not have the seat tube slightly undersized. heat it to expand, insert clamp, and then leave to cool and have it hold on a friction fit?
(I don't trust araldite)

Wait; hang on, you are going to cut the head off a seat post to glue another head on to it? Hello.

have i missed something.

Seatposts of that type (forged clamp section into pipe) are usually cryofitted together just like fork crowns/steerers etc, which you will really struggle to do at home (or even in a decent engineering workshop!).

So you want a seatpost to fit a 24mm frame?
Buy a cheap/used 1"/25.4mm seatpost and get it machined down, someone might charge you £10 for the pleasure. Much safer and more logical I'd have thought?

A seat post is not a part that I'd want to fail.

I remember some guy who was bugging all of the cycling site admins circa mid-2007 to basically plead with us to not promote cycling as it wasn't safe.

The reason was that he'd not maintained his bike, and that his seat post had slipped into the seat tube during a ride. The result of this was that his body weight went from saddle to leg before he could react and engage his muscles. The effect was that he snapped his lower right leg and the bone came straight through the flesh and left him in a crumpled heap beside his bike in agony. He was incredibly traumatized by this, so some 9 months later he was still emailing new cycling sites to warn cyclists of the dangers.

Now I remember thinking: Dude, this is your fault... you didn't maintain your bike. So largely ignoring it and not indulging in scare-mongering by repeating it on the site.

But in this case of a custom seat post I do recall that interaction and how queasy it made me feel. And whilst ensuring the seat post clamp is secured is certainly a maintenance issue it's not a surprise that I now buy Thomson seat posts.

Sure, make one... but make sure you understand the forces involved and issues involved. I'm pretty sure it's not just "stick a tube on this, and in here".

^ Yup, any component failure is bad, but contact points (bars/stem/post/pedals/crank) when they fail, you fail. Hard.

I broke my ankle when a pedal axle snapped during a landing (only about 4-5'), it gouged what could only be described as a TRENCH into my inner calf before inevitably running over my own foot, breaking various bits, then wrenching me off the bike into a tree which pulled my shoulder out.
The cause? my own stupidly for borrowing someone elses trashed pedals on the day with unknown history. Learned from this and now usually only buy new contact points, or good used that I know the history of. I.E. well used carbon seatpost/bars/fork would scare the shit out of me.

. Learned from this and now usually only buy new contact points, or good used that I know the history of. I.E. well used carbon seatpost/bars/fork would scare the shit out of me.

that is rather odd thinking given that CF has far and away better fatigue life than steel/aluminium.
I'd be happier with a well used CF seatpost than a well used lightweight aluminium one. I've a pair of Mizuno Fiandre 1" forks on my ti bike & the steerer column wall is thicker than anything you'll have seen, so thick all propriatary bungs were too wide.
I've absolute confidence in it at 50mph downhill descents and have done so for many years and I'm no lightweight (think 1.5 wiggo's..lol)