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Old 05-16-12, 06:35 PM   #1
cyclocello
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Shaving a 27.2mm seatpost down to 26.6?

I have an older bike that rides beautifully, and works with a plastic/foam seat with longer rails. However, I just bought a brooks saddle, and unfortunately the rail length is too short.

This prompted me to buy a VO grand cru seatpost with longer setback (probably more than I really need.. 30.2mm possible). I naively bought a caliper without knowing how to measure and thought it'd fit.. but nope, I have a 26.6mm (after figuring out how to read the caliper correctly, I read the diameter as 26.5mm but Sheldon Brown say's an '81 Nishiki International has a 26.6 diameter).

This modern alloy seatpost has a wall thickness of about 2.7mm. Would hiring a machinist with a lathe to shave it down to 26.6, a full 0.6mm, compromise the seatpost? I weigh at or less than 190lbs.

Thank you!
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Old 05-16-12, 06:46 PM   #2
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Is a guarantee you won't have to poop into a bag held by a shoulder sling for the rest of your life worth the $20 for a new seatpost?

I'd say that's pretty cheap insurance. Buy a new post.
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Old 05-16-12, 06:54 PM   #3
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Is a guarantee you won't have to poop into a bag held by a shoulder sling for the rest of your life worth the $20 for a new seatpost?

I'd say that's pretty cheap insurance. Buy a new post.
+ a zillion!
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Old 05-16-12, 07:02 PM   #4
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The answer to your question is simple; don't do it.
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Old 05-16-12, 07:14 PM   #5
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just buy a Kalloy seatpost, in the size you need.

Or..

You could get a chromo Redline 1" nice steel..
your machine shop can turn a 1" ID tube down OD to fit your frame ID

I found , setback gained by a couple Brompton parts.

Saddle adapter pin on top, also steel, provides a horizontal tube,
onto which Brompton's excellent saddle clip is fitted..
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Old 05-16-12, 07:17 PM   #6
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just buy a Kalloy seatpost, in the size you need.

Or.. You could get a chromo Redline 1" nice steel..your machine shop can turn a 1" ID tube down OD to fit your frame ID..
+1 on the Kalloy. -1 on turning down a 1" steel seatpost since 1" is 25.4 mm which is already too small for his frame. I've never seen a lathe make anything bigger in diameter.
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Old 05-16-12, 07:22 PM   #7
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That is a tremendous amount of work I did it once for my trek 990.
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Old 05-16-12, 07:32 PM   #8
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If you have access to an adjustable reamer the way to do this is to ream the seattube... not the seatpost unless you have access to a lathe or something but with a file?? i warranty you the seatpost will get octagonal instead or rounded hehe...

Get a new seatpost man, a used one is super cheap.
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Old 05-16-12, 08:35 PM   #9
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If you have access to an adjustable reamer the way to do this is to ream the seattube... not the seatpost unless you have access to a lathe or something but with a file?? i warranty you the seatpost will get octagonal instead or rounded hehe...

Get a new seatpost man, a used one is super cheap.
+1. Older bike shops will have a selection of seatposts in varying diameters. New ones are available in various styles:
http://www.niagaracycle.com/index.ph...h=4_414_414012
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Old 05-16-12, 09:56 PM   #10
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hill-ride..
Nope describing machining the shim around the seat post, not the seat post itself..

but the shop catalogs have 1" ID Shims, in a few outside dimensions
you have to request the shop to order them, from their suppliers..

UK based USE makes a 25.0 seat post and shims up to all the bigger sizes,
are machined and anodized high precision , in 0.2mm increments.
They make a 27.2, and more shims to use it in even larger frames .
It is a common manufacturing procedure..

I can imagine an aluminum shim in a steel seat tube ... even if the corrosion&rust
sticks the shim to the frame, aluminum-aluminum surface between shim-sleeve and
seat post would still move up and down.
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Old 05-17-12, 07:58 AM   #11
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hill-ride.. Nope describing machining the shim around the seat post, not the seat post itself...
Yeah, sorry about the misunderstanding. Re-reading your posting I see what you were actually recommending. However, buying the right diameter Kalloy post will probably be cheaper and more satisfactory.
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Old 05-17-12, 08:18 AM   #12
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Wow! Is the 70's again when finding and purchasing such a seatpost would require a sizable investment in time and effort calling around, and a lengthy wait?

Lordy man! You can have the right post delivered to your door with just a few mouse clicks, and it will cost less now than it would have in the 70's! DO IT.
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Old 05-17-12, 09:22 AM   #13
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If mouse-clicking my way to a new seatpost was so easy, I wouldn't have made this thread!

I've been looking for a 26.6mm. The grand cru has a setback of 30.2mm.. I probably at the most need 25mm. As I've found already, there doesn't seem to be a new seatpost at that diameter with that amount of setback.

fietbob the brompton adapter would def work! but I guess being retro and using a leather saddle would make that pretty odd looking. If I have no other choice, the extension adapter is the way to go though.

ultraman I never thought of reaming the seat tube.. that seems kind of crazy but like the first replier said I'd rather not have a **** bag for life!

I have access to a lathe, but I don't think a reamer.
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Old 05-17-12, 09:36 AM   #14
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Just the setback may be short, on Kalloy,
the SAP/saddle clip combination still offers ,
on the plain top post, , setback as an adjustment

Upright rider posture, Dutchafying make it fit
women by making the seat tube 77 degree, oldframes,
have used this combination..

I understand the OP's issue .. went the opposite
A B17 had to go, when I felt I was a rivet sitter,
on a zero setback suspension seatpost, so I traded away the saddle.
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Old 05-17-12, 09:47 AM   #15
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http://www.amazon.com/Kalloy-Laprade.../dp/B001CJV7AK

14 $
20mm setback
you could probably make up 5mm with moving the saddle back a bit further on the rails
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Old 05-17-12, 09:57 AM   #16
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or could you find a 25.4 post with larger set back and shim it to 26.6
http://www.amazon.com/Sunlite-Alloy-...269872&sr=1-35

http://www.planetbmx.com/shop/bike-c.../prod_819.html
super laid back and you can use your original Brooks saddle clamp
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Old 05-17-12, 10:07 AM   #17
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If mouse-clicking my way to a new seatpost was so easy, I wouldn't have made this thread!
cbchess beat me to it. You really need to learn to craft searches. I scored the same one he did on the first try.
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Old 05-17-12, 11:09 AM   #18
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I tried it. Buy a new one.
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Old 05-17-12, 12:28 PM   #19
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The way to do it is to ream the seat tube little by little. If you use a lathe then will make your life easier but hard part will be to have the chuck to hold the head of the seatpost. You dont need to "lathe" the whole seatpost just do what will be inserted.

A tiny detail, no idea how compromise the seatpost will get if you use a lathe to remove the extra material.


Quote:
Originally Posted by cyclocello View Post
If mouse-clicking my way to a new seatpost was so easy, I wouldn't have made this thread!

I've been looking for a 26.6mm. The grand cru has a setback of 30.2mm.. I probably at the most need 25mm. As I've found already, there doesn't seem to be a new seatpost at that diameter with that amount of setback.

fietbob the brompton adapter would def work! but I guess being retro and using a leather saddle would make that pretty odd looking. If I have no other choice, the extension adapter is the way to go though.

ultraman I never thought of reaming the seat tube.. that seems kind of crazy but like the first replier said I'd rather not have a **** bag for life!

I have access to a lathe, but I don't think a reamer.
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Old 05-17-12, 12:44 PM   #20
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that shoulder where you stop turning down the OD, becomes a likely breaking point.

I used the Adjustable reamer at the LBS, to shave 0.2mm out of my RB1 frame,
so It accepted the 27.2mm seatpost I had in my hand.
online search, looks like they, the reamers, China, no doubt, are about $80.
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Old 05-17-12, 04:29 PM   #21
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Very helpful advice, I didn't think of shimming up from a smaller dia seatpost. Thank you all!
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