Welding practice today

I work full time, but today I have annual leave (holiday), so I have been practising my TIG welding.

When welding the dropouts and parts of the pivot, I will need to join thick steel plate (4mm or 5mm) to thin wall tubing.  Melting the plate whilst not destroying the tubing is challenging.  My first efforts were, as expected, poor.

Things improved however.

I'm at the stage now where most of my welds are OK, but I still have an occasional disaster.  I'm trying to become consistent, as its possible to ruin hours of work with one bad weld, or by putting too much heat in and distorting the assembly.  Practice, practice...

My provisional design

I am sure that this design will change as the project progresses, hopefully based on comments from previous, more experienced builders.

Design principles:

• Rideability
• Ease of welding / alignment
• Mechanical simplicity
• Low weight

I will use rectangular section steel tubing and steel plate.

• Front part:  30x10x1.5,   40x20x1.5,  40x40x1.5
• Rear part:  40x20x1.5
• Pivot:  Steel plate with two Heim joints.

The wheels will be 20 inch (406) with rims for 50mm (Big Apple) tyres.

The rear hub will be a Sturmey Archer X-SD tricycle drum brake hub, allowing the rear part to be single-sided.

The drive will be a conventional derailleur system, initially with a Flevo bottom bracket for adjustability.

Resources

Information on the web about python construction and riding are concentrated into a few places.  I have found the most useful of these to be:

http://en.openbike.org/wiki/Main_Page

This Wiki has links to all the other resources that I found to be useful.  Thank you to all the python builders who have devoted their time to document what they have done in order to make the task of those who follow so much easier.

The best resources for learning to TIG weld are to be found on Youtube.  There are a large number of useful videos, which I have found to be invaluable.

The workshop

The workshop is very small.  It has a plastic roof, little ventilation and no heating.  It is very hot in summer and very cold in winter.

My steel surface for welding is small - working on assembled sections of the bike will be a challenge.

My welding machine is a cheap DC TIG machine.  The pros of TIG are that there is more control on thin steel sections and it is relatively clean (no fumes) in comparison to MIG and stick.  

The con is that it is difficult to learn.

A little bit about why....

I started cycling about 10 years ago, commuting and easy touring with my partner Sarah, who has always been a keen cyclist.

About 2 years ago Sarah bought a proper road bike and joined a cycling club.  A few months later I did the same.  Sarah has now moved up a gear and participates in Audax cycle events of up to 600km.  I, however, find that the posture of an upright bicycle does not suit me and despite many adjustments, 100km is about the longest distance that I can 'endure'.  I would like to cycle further.

Whilst investigating recumbent bicycles, I came across python recumbents.  The idea that it was not possible to buy one of these (you have to construct it yourself) was very appealing as a project, probably as a stepping stone to constructing a more conventional recumbent.

I have always enjoyed making and modifying things and am a competent bicycle mechanic.  The main barriers were the lack of a suitable workspace and that I cannot weld. I have now made a workshop in a lean-to at the side of our kitchen.  Progress in learning to weld to follow...