From: Mark Bulgier <bulgier@oz.net>
Newsgroups: rec.bicycles.tech
Subject: Re: 853 seat tube reaming
Date: 14 Jul 2001 08:08:56 GMT

I believe (without a lot of evidence) that many frames that say they are
made of 853 use something else for the seat tube, precisely because of the
difficulty of reaming.  Ditto for head tubes.  It can get harder locally
than the blades of a HSS reamer.

As Orin points out, there likely is a welded-on piece of regular Cr-Mo at
the top, due to the rather thick wall at the top, so reaming will probably
be OK, but I'm not sure I'd want to find out by trying it with *my* reamer
- if it really is 853 it'll ruin the reamer in no time.

When I was at Match, where 853 Schwinn Paramounts were made for a time, we
used real 853 seat tubes but honed them instead of reaming.  I'm not
talking about the ubiquitous "flex hone", but a real, rigid-adjustable
stone honing machine, probably cost Tim a thousand bucks used.  This was a
secret at the time but I suppose it's OK now as Match has been out of
business for some time now.  Those bikes had the smoothest seat post bores
I'd ever seen, in over 20 years as a framebuilder - sweet!  Pain in the
neck (literally) to do though, and the honing stones only lasted through
about 10 frames before they needed to be replaced, a slow and expensive
process.

Mark Bulgier

From: Mark Bulgier <bulgier@oz.net>
Newsgroups: rec.bicycles.tech
Subject: Re: 853 seat tube reaming
Date: 15 Jul 2001 05:07:27 GMT

 Andrew Bradley wrote:

> I have an 853 frame, but can anyone explain the advantage of such "hard"
> steel is? Is it better than 753 in some way?

Hardness and strength aren't the same thing but there's a high degree of
correlation.  The advantage of air-hardening alloys like 853 isn't so much
the hardness per se, but rather the strength.  The main difference is the
strength in and near the joint, which in the case of 753 is much lower than
the as-delivered strength; where 853 is actually stronger after welding or
brazing.

853 still has a tempered zone that's weaker than as-delivered, but it's a
few mm away from the weld, or maybe a cm away from a brass braze, so the
weakest point doesn't occur right at the toe of the weld, or right at the
edge of a lug or fillet.  I've seen some evidence that even the tempered
zone of welded or brass-brazed 853 is stronger than that of silver-brazed
753.
--
Mark Bulgier