Adding the rear frame to the plug

Up to now all bonding has been done horizontally on a flat table to ensure the frame will be straight and level. To mount the rearframe the plug is put vertically onto a table using reference lines on the table surface.


Lots of weights and straight-edged objects are used to ensure that the frame will end up in one line.
From the front:

To the rear:

It should be one straight line.

Making the front part of the foam plug

The bike will be a one-off, so building over a positive plug is the easiest way to build it.
I use PU foam that is relatively stiff. It is easy to shape by cutting and sanding.
First the design is outlined on the foam.



Then the foam is cut to shape:

The intermediate head tube is bonded to the foam parts.

And the front tube and head tube are bonded to the foam.
All connections are bonded with epoxy, filled with glass spheres and cotton. The uncured epoxy is covered with peelply to make a nice bondable surface.

Building the front tube of the frame

The stoker cranks are mouted on an extendable boom. For simplicity I use a readymade boom from a recumbent supplier. On the front of the frame I need a tube that slides around this boom.

To do this a carbon fibre tubes with integrated clamping flanges has been made using the boom as a mould. As it is nice to be able to separate mould and tube, I cover the boom in cling film.

A couple of hours work later 6 layers of 200gr/m2 carbonfibre cloth are covered with peelply in a vacuum bag.

The end result is 130 gram of very stiff clamping tube.

Preparing the metal parts

Building starts with preparing the metal parts. I use the rear frame and the head tube of the Santos frame, and a straight aluminium tube as head tube for the handlebars.

The first work is chopping up a perfectly good frame. The first strokes of the saw are difficult, then there is no way back anymore.


All parts are covered in a thin layer of glass / epoxy. This increases the bonding between the fibre parts and the metal, and it prevents electrical contact between carbon fibre and metal, which could lead to galvanic corrosion.

After laminating the glass the parts are cured at room temperature in a vacuumbag. The vaccuum pump is made from a fridge compressor. Using vacuum increases the quality of the laminate considerably.

Why a homebuild bike?

Years ago a made many bikes, all of them recumbent like the tandem shown here. I love to design and build, and I love the feeling that I am travelling on someting that I made myself.

Commercial products are quite expensive (the Pino is not available below 3000 euro), and designed with an adult stoker in mind. So I decided on starting out from scratch.

The most important design requirements:

• Not to much work to build, use off the shelf parts where possible
  
• Carbon fibre composite construction, as I love the material
• Total length less that 2 meters for transport on a bike rack on the car
  
• Suitable for kids from 3 to about 10 years old
• Stoker freewheel, so the kid does not have to pedal
• Elegant lines

Making a good rear triangle is a lot of work in carbon fiber, so I decided on using a good mountainbike rear frame instead. I contacted Santos Bikes, a dutch builder of custom bicycles. For years we have been riding one of their tandems.

I asked for a damage frame with an intact rear triangle. They liked the idea, and in the end I got an almost perfect new frame with a slight blemisch in exchange for a CD with photographs from our recent Thailand trip. A really nice deal.

A lot of design work resulted in this drawing:

I admit, it is sketchy, but for me enough to build a bicycle.

What is a semi-recumbent tandem?

A semi-recumbent tandem is a tandem bicycle with a recumbent front rider, and a normal positioned rear rider. Usually, the rear rider is the captain (steering) and the front rider is the stoker. Commercial products are the Pino by Hase and the Viewpoint made by Bilenky.

After a couple of years touring with a normal tandem and the kids (now 3 and 5) in a chariot, we need a new solution that allows our eldest to pedal and offers more space than the chariot she has outgrown. The most common solution is a trailerbike behind a conventional upright bike. There are several drawbacks:

• the child is behind you out of view
• the child can not do anything else when riding
• the stability of the combination is limited, especially with full luggage
• I do not own a proper upringt bike, so a new bike is due anyway
  

For us the semi-recumbent a clearly the better solution. The child is on the chair in front of you, seatbelts prevent an accidental drop, and reading or drawing while riding is not a problem.