Frame Build Part Two

A very British motorbike

With the engine set up in the jig, the next step is to bend, shape and weld the tubes that make up the Enigma 1050 chassis. These are the materials and processes involved.

T45 steel tube for the Enigma 1050 chassis
The Tubing

Tigcraft have chosen T45 tubing for the Enigma 1050 chassis. The wall thickness of the tube is 16 SWG (Imperial Standard Wire Gauge) which equals 1.626mm. The sheer mass of the engine makes substantial tube necessary. T45 is a cold drawn, seamless tube. The cold drawing process involves taking manufactured tube then drawing it through a die to produce the required diameter and wall thickness. Cold drawing results in dimensionally precise tube with a good surface finish. The process of cold drawing alters the crystal structure of the metal in such a way that the strength of the material is increased.
T45 tube is made from an alloy of steel, carbon and manganese. It has a high strength to weight ratio and, unlike chrome molybdenum steel, does not require heat treatment after welding. T45 tubing is used extensively for bicycle frames, racing car chassis and, of course, motorcycle frames. It is also used widely in the aircraft industry.

Tube Shaping

Dave Pearce of Tigcraft reckons that the Stakesys Hole Saw Tube Notcher is the best two hundred quid he’s ever spent on a piece of tooling. When you join two pieces of tube, they have to meet precisely and this is where the notcher comes in.
“You can use a file and a hacksaw to achieve the same result,” says Dave, “But it takes forever and you end throwing a lot of tube away when you get it wrong.”
To use the notcher, you select a hole saw of the same diameter as the tube you want to prepare, set the angle of the tool to the work to the same as the angle of the tubes to be joined then cut the notch. The tool is powered by an electric drill. The shaft which holds the cutter rotates on needle roller bearings in a substantial aluminium alloy housing which ensures both accuracy and longevity.

Stakesey tube notcher
Tig Welding schematic drawing for Engima 1050 British motorcycle
Tig Welding

TIG welding (Tungsten Inert Gas) is the best method for joining tubes on a motorcycle frame. As the diagram shows, the heat is provided by a tungsten electrode which completes an electrical circuit with the material to be welded. An inert gas (usually but not always Argon) is fed to the weld area through the housing which holds the tungsten electrode. The gas ensures that no oxygen can reach the joint which results in a pure, strong weld. Filler rod is fed manually into the molten pool to complete the joint. The temperature of the arc can reach as much as 3000°C which is some way below Tungsten’s melting point of 3410°C.
Compared to braze welding (also know as bronze welding) TIG adds less metal to the construction and is, therefore, lighter. Dave Pearce reckons that a couple of kilos can be saved by using TIG instead of braze welding.

That’s the basic info. See how it gets put into practice here.

Enigma 1050 – a very British motorcycle being built in Hampshire, Derbyshire, Leicestershire, Berkshire, Wiltshire, Surrey, Sussex, Suffolk, Shropshire and Cambridgeshire.