Custom seatpost shim, 27.3 (three) to 29.6?

[Winterflaw]

Hi.

I want to buy a titanium seatpost.

There are a few out there, but there are various issues for me with all of them, except for a seatpost made by Enigma.

They have a few prototypes, which were delivered last week.

They are ideal except that there was a manufacturing error, and instead of being the standard 27.2mm, they are 27.3mm.

My seatpost tube on the bike is 29.6mm.

Obviously, 27.3mm seatpost shims as such do not exist.

Any suggestions on ways to handle this?

I have a USE 27.2 to 29.6 plastic shim.

I've thought about a custom shim, but no one has a service to make them, at least not on the net. I also expect it will be expensive. I've thought about 3D printing, but I'm not sure the plastic will be the right sort, and real shims have a slit down their entire length; the 3D shim I've seen only has a slit down part of its length, I presume due to manufacturing limitations. I've thought about thinning the USE shim by 0.1mm, but I have no idea how I would go about doing so.

[profpointy]

you could use aluminium drinks can. Not sure on exact thickness but easy enough to measure or just use trial and error

Or, you could buy some 0 .15mm shim strip from an engineering supplier

[rjb]

you could use aluminium drinks can. Not sure on exact thickness but easy enough to measure or just use trial and error

coke cans are 0.1mm thick or 4 thou in old money. (0.004")

Could you wrap some emery paper around a marginally smaller tube then insert into the plastic shim and twist it until its right. After all you will only need to remove 2 thou to get it right. Have you tried the seatpin in the frame with the existing plastic shim. The amount you need to remove may well be within the manufacturing tolerance and it may all fit satisfactorily.

[Winterflaw]

you could use aluminium drinks can. Not sure on exact thickness but easy enough to measure or just use trial and error

Or, you could buy some 0 .15mm shim strip from an engineering supplier

Thankyou for the idea. I may be wrong, but I think you might have got things the wrong way around? the seatpost is thicker than the shim, rather than thinner; it's not padding I need to add, but rather - if the solution was in terms of adding or removing - but remove from the shim.

[Winterflaw]

Could you wrap some emery paper around a marginally smaller tube then insert into the plastic shim and twist it until its right.

Ah, to erode the shim! that is an interesting idea.

I still have the existing, broken, 27.2mm seatpost. I think I could wrap that in paper, and then try to slide the shim over it. It should stretch a little, to go over, and then I could try spinning the shim over the seatpost/paper combination.

Have you tried the seatpin in the frame with the existing plastic shim. The amount you need to remove may well be within the manufacturing tolerance and it may all fit satisfactorily.

I have not bought the seatpost, so, no.

I don't feel very happy about this as a solution, because I'm concerned about the possibility it all seems to work but in fact there is an unusual and unexpected pressure from the over-thick seatpost, which will constantly apply load to the frame and in particular to the wields.

[Winterflaw]

These people;

http://www.racewaredirect.co.uk/

Tell me they can make custom shims in nylon for 35 GBP plus shipping.

In conversation with them now - colours, shim design, length, collar design, slit/slot design, etc.

[Brucey]

the problem is that none of the parts you have are likely to be exactly 'size' anyway. Hence trying the parts you have is a good idea, and getting a shim made remotely (to some notional size) is unlikely to give a really snug fit.

FWIW I think a few minute's work with some 400 grit paper and you could make a shim that is the 'wrong size' work just fine.

cheers

[Winterflaw]

So, what happened in the end is that I sent the seatpost back to USE, and where I have quite a bit of spare length, they have taken off the very top of the seatpost, where the broken part of the seatpost is, and they are bonding in a replacement.

35 GBP rather than 150 for a new post.