External butting on 525

[fossala]

I picked up a frame on here and it arrived this morning. If you look at the attached picture it looks dented but it goes all the way round the tube and it’s not deep enough to feel, it just catches the light. Did Reynolds ever externally but tubing, could it be paint? The only way I could think it is damage is if something was clamped to it, shows no marks if this though.

[Brucey]

if the external diameter of the tube changes (i.e. so the last few inches are larger diameter) then one possibility is that someone has welded a seat tube in where the top tube should be. Seat tubes meant for TIG welding are usually externally butted.

cheers

[fossala]

Got my callipers out. It must be externally butted as it increases by 1mm from the mark up to the fillet braze.

[fossala]

if the external diameter of the tube changes (i.e. so the last few inches are larger diameter) then one possibility is that someone has welded a seat tube in where the top tube should be. Seat tubes meant for TIG welding are usually externally butted.

cheers

It’s a Dave Yates frame so he’s not really know for poor work.

[Brucey]

it may have been deliberate, who knows

cheers

[fossala]

You may be right as the seat tube is the same diameter 28.7 expanding to 29.7/8mm

[531colin]

You might expect the vendor to know?
Maybe its a big frame built for a big rider who wrestles the bars all the time?
Or somebody whose life has been marred by shimmy?

[fossala]

You might expect the vendor to know?
Maybe its a big frame built for a big rider who wrestles the bars all the time?
Or somebody whose life has been marred by shimmy?

Possibly, the tubing isn’t thin by any means. Sturdy touring bike with the weight to match.

[Valbrona]

Only seat tubes were externally butted.

But hey, a tube is a tube and a butt is a butt.

[slowster]

What is it like to ride, both unladen and with fully loaded panniers?

[531colin]

525 seat tubes are 28.6 OD except for the bulge; wall thickness is 0.9/ 0.6/ 1.2mm (1.2 for the external butt, for all the welding/reaming))
28.6 double butted tube is available in (light) 0.7/0.4/0.7mm and regular 0.8/0.5/0.8mm: also a single butted 0.9/0.6mm (why?)
I would guess the downtube is 31.8 or maybe 34.9mm OD, both of those are regular 0.8/0.5/0.8mm
The differences in wall gauge are relatively slight and diameter has a greater effect on the stiffness of the tube, so I have to say I'm a bit puzzled as to why you might use a seat tube in place of a top tube.
(more recent Spa frames have the front end of the top tube ovalised in order to gain a bit of lateral stiffness (against shimmy) for no extra weight .....who knows if it works?)

[Brucey]

isn't the SB 0.9/0.6 tube one you might use as a seat tube in a lugged frame?

cheers

[531colin]

isn't the SB 0.9/0.6 tube one you might use as a seat tube in a lugged frame?

cheers

Which end has no butt? The pedalling end (where a seat tube fails if its going to fail) or the reaming end?
.....not really comfortable with either, but then no experience of butted frame construction!

[Brucey]

no butt at the top. That is how you end up with 27.4mm seat pins in some lugged frames.

Back when fashion mandated that seat pins were shorter, bending loads into the seat tube from the seat pin would normally be a fair bit less than would be considered 'normal' today. Back in the 1960s campag listed a very short seat pin as 'standard length', and the one then listed as 'long' was only just long enough by the 1980s.

cheers