Re: [CR] modifying old bike parts


Example: Framebuilders:Alex Singer
In-Reply-To: <4A4E48AD.70200@mchsi.com>
References: <623670.49677.qm@web83006.mail.mud.yahoo.com>
Date: Fri, 3 Jul 2009 12:37:46 -0700
To: Eric Burns <theej@mchsi.com>, Brian Van Baush <bvanbaush@ameritech.net>
From: "Jan Heine" <heine94@earthlink.net>
Cc: classicrendezvous@bikelist.org
Subject: Re: [CR] modifying old bike parts


At 1:06 PM -0500 7/3/09, Eric Burns wrote:
>Brian Van Baush wrote:
>>I'd like to caution against modifying old parts to fit your old bike frame.
>>If you machine a seatpost, brakes, stems, etc your removing material and
>>possibly putting yourself in an unsafe postion if the part fails in use. The
>>same caution applies to any frame with a dimple at the down tube, a sign of
>>the frame being in an accident.
>>
>>Just my two cents, have a safe weekend.
>>
>>Brian Anacortes, WA USA
>>
>
>
>Brian,
>
>I posted about turning down a 25.4mm post to 24.5mm.
>
>.9mm equals .036 or .018 per side, a difference that could be
>handled with sandpaper if one was patient enough.

0.45 mm does not sound like a lot, but it can represent a significant chunk of metal. If you tried to remove that with sandpaper, you'd spend a good while. And if your seatpost walls are only 1.5 mm thick, you are removing roughly 1/3 of the material!

I have turned down seatpins, but those were 450 mm long mtb seatpins, and I cut them down to about 1/3 their length... which means that the stresses on them were much lower. I still left them a bit thicker than the wall thickness of original 1950s seatpins I was copying, just in case the 1950s material was of a higher strength.

Campagnolo used to offer different seatposts with different wall thicknesses. I don't know if the material is the same, but if it is, then turning down the seatpost should be fine.

Question: What kind of frame accepts a 24.5 mm seatpost?

Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.vintagebicyclepress.com