I have been taking my bike on planes for more then 2 decades now - unfortunately airline restrictions are getting harsher and harsher and as a result it is very difficult getting away without paying extra fees due to the size of the packed bike. It is unfortunately also getting more and more difficult to get bikes on trains, busses or other form of public transport.

The largest part to pack is always the frame.

There are a few commercial solution out there to split a frame so the bike can be packed in an airline compliant way. Unfortunately these are all on the expensive side and honestly what is the point to pay 1000+ Euros (e.g. S&S couplings) if you want to go to places where bikes are potentially stolen, fall of buses or are facing all kind of other threats.

The ultimate trigger for me to get the project going was a trip to India where I wanted to travel by public transport with my partner for about 3 week and then cycle down form Leh back to Delhi. This was simply not feasible without a bike packed in a compact way.

Tools you need:

something to cut Steel tubes: e.g. Hacksaw, tube cutter
a drill for metal, preferable with a stand
a hammer / mallet
sliding caliper

Materials:

a suitable frame
clamps fitting the tube diameter
reinforcements for the tubes (steel tube of fitting diameter)
steel pins

Step 1: Cut the Frame

I used a Voodoo Wanga - a nice old steel frame that I bought second hand a couple of years ago. it has butted main tubes which turned out to be slightly problematic.

If you follow this guide please:

Do not use a super expensive frame - or at least don't blame me if something goes wrong.
I would recommend to do this with a Steel frame only - Titanium should work, Aluminium could, Carbon - I would definitely advise against.
Straight tubes would make the fittings inside the tubes easier.

Before you engage with the project keep in mind you need something to clamp the frame together after it has been cut.

My frames upper tube has an outside diameter of 32mm and the lower tube is 35mm. These are the same measurements that stunt-scooters use for their headset (or at least close enough)

I got the clamps on amazon (31.8mm and 34.8mm). The bigger one actually comes with an adaptor which came in handy as well. Total cost 20 Euros.

As the top tube clamp "only" needs to align the tubes (no pull) it can be a lighter (red)

The bottom tube needs to be able to handle all the pull - so I went for a quite solid one (blue).

(Yes there is torsion on both tubes as well but I found that not relevant so far)

Depending on the frame diameters there are other options out there - don't give up if you have to search a bit longer!

To figure out where to cut the frame check the dimensions you need. Close to the seat tube should be the normal choice. Consider any cable guides, holes for bottle cages, cable routing... Also check - tubes are often deformed close to the seat tube! If you have butted tubes stay close to the seat tube - the tubes are thicker there and will give you less headache.

As soon as you decided where to cut you need to decide how to. Keep in mind that any material that is cut out will be missing and has to be covered by your clamps.

Hacksaw - downside you lose the thickness of the blade (1 mm more if you don't cut clean) in tube length - only a potential problem at the top tube.
Tube cutter - the resulting cut is bent inwards and needs attention so the inserts fit. Also thin steel tubes bend like crazy while being cut - which gave me almost a heart attack - and it takes forever.
I guess you could also use a dremel tool if you have a steady hand - same problem as with the Hacksaw though.

Step 2: Reinforcing the Tubes

When I first assembled the frame I realised (too late!) that the clamps deform the frame. This would make the joint too weak - specially lower tube.

To support the forces applied by the clamp I inserted a steel tube of fitting diameter (made from a table leg - 3 Euros) roughly the length of the clamps (about 5 mm more on each side).
In the down tube I used the spacer that came with the larger clamp and inserted that in between the steel tube and the frame tube but a fitting steel tube would be preferable.

After more testing (light riding and frequent checking) I finally

cut the lower clamp to 75% of its original length (weight saving)
added pins in the lower clamp as this is the one that is pulled apart. As described in the picture the pins go all the way through. Lower one is permanently inserted in the lower half of the clamp. The second one is removable in the upper half of the down tube. The pins are actually made of an old spoke (2mm INOX)

The removable pin is also a safety indicator. It can turn freely in the hole. Should the frame move in the clamp due to stress then the spoke would be squeezed and would no longer turn - this would give an early waning and trigger a detailed check as a failure during a downhill would most likely result in bad injuries. Nothing ever moved so far!

The black marks have the same function for visual inspection.

Step 3: What Is It For?

Folding the bike takes quite a lot of time (30 min if you know exactly what your doing!)

Depending on how small you want to pack you have to:

removing both wheels
removing crank
removing rack
taking care of all the cabeling
removing handlebars
removing fork
removing saddle

If you want to pack your bike in a similar size bag as I used you will need some time and experiments to fit everything - specially the rack is always a headache.

You could off course just split the frame while everything else is still attached (careful with the cables) or do whatever solves the transport problem at hand.

Bottom line this is a hack for travelling and not fit for commuting needs.

Step 4: Experience and What I Would Do Different Next Time

I used the bike for a few rides on my local mountain. Manly off road, mainly up or down. I was avoiding fast downhills on bad roads as the forces on the frame would be much larger.

After my initial testing I found no real limitations and was confident to take the bike to India.

During my trip I covered about 1000km on largely bad roads most time up or down - never extremely steep. I weight about 85kg, luggage 15kg, bike 14kg - so good 120kg system weight. Nothing ever moved or gave me the slightest reason to worry about.

I got loads of jealous comments from other bikers though!