I am going to cut a bicycle frame in two.

The frame has a spar main section of a taller-vertically rectangle with
half-rounds on the top and bottom; this is place for the cut. I'll make
a matching inner sleeve for both alignment and tightening.

There is a vertically-coplanar tube joining this spar at an angle of
about 20 degrees. I will run a rod though this tube and it will cross the
joint into the sleeve holding a captive nut.

Does the angle of the cut matter - 90 to the spar, 90 to the rod, half-
way between?

I have a bit of latitude with lateral placement of the cut, so I could
arrange for the rod to cross the joint other than centred. The weight
would tend to open the bottom of the joint first, would a lower crossing
be better?

On Tue, 26 Jun 2012 17:20:16 +0000, xpzzzz wrote:
I am going to cut a bicycle frame in two.

The frame has a spar main section of a taller-vertically rectangle with
half-rounds on the top and bottom; this is place for the cut. I'll make
a matching inner sleeve for both alignment and tightening.

There is a vertically-coplanar tube joining this spar at an angle of
about 20 degrees. I will run a rod though this tube and it will cross the
joint into the sleeve holding a captive nut.

Does the angle of the cut matter - 90 to the spar, 90 to the rod, half-
way between?

I have a bit of latitude with lateral placement of the cut, so I could
arrange for the rod to cross the joint other than centred. The weight
would tend to open the bottom of the joint first, would a lower crossing
be better?

Your description isn't clear enough for me to tell what you mean
or what you want to do. Is the "spar main section" a part of the
top tube, or a part of the down tube? (See terminology at
http://en.wikipedia.org/wiki/File:Bicycle_diagram-en.svg.)
What is the name of the "vertically-coplanar tube"? Is it the
seat tube, head tube, or some other thing?

Is your goal to cut the bike in half for easier transport and
add connecting rods that allow reassembly so the bike can
still be used? How much weight will the joint have to carry,
and what are the height and width of the spar section?

--
jiw

On Tue, 26 Jun 2012 19:57:20 +0000, James Waldby wrote:

Your description isn't clear enough for me to tell what you mean or what
you want to do.

http://www.bikecult.com/works/archiv...tonminiKD.html

Cut is to be in the main tube somewhat forward of the place where the
(nearly) horizontal joins; I have removed the rack section rearward of
the three-tube junction, and the rod will start there and run forward
through the (nearly horizontal) tube towards the cut.

On Tue, 26 Jun 2012 20:35:02 +0000, xpzzzz wrote:
On Tue, 26 Jun 2012 19:57:20 +0000, James Waldby wrote:
Your description isn't clear enough for me to tell what you mean or what
you want to do.

http://www.bikecult.com/works/archiv...tonminiKD.html

Cut is to be in the main tube somewhat forward of the place where the
(nearly) horizontal joins; I have removed the rack section rearward of
the three-tube junction, and the rod will start there and run forward
through the (nearly horizontal) tube towards the cut.

It looks like cutting perpendicular to the axis of the big tube
is the easiest thing to do, and if you use a coupler like the one
shown in http://en.wikipedia.org/wiki/Bicycle_Torque_Coupling
probably is what you would have to do. However, it probably
would make sense to get oval tubes from junk bikes, make up
several junctions with cuts at different angles, then stress
them (with known weights) until they break.

--
jiw