Small Penny-Farthing.


This project came about after two different sized bicycle wheels were spotted while clearing out the garage.

A slightly insane project and the most useless thing I've ever made, but it did provide some fun machining and required some interesting design work in places.

 

 

 

 

 

 

 

 

Inspiration parts.

The plan was to base the design around a 700c front wheel and a 12" rear wheel.

The frame would be a 1" steel pipe curved to suit and fitted with the forks from the 12" wheeled bike to hold the rear wheel. A pair of standard front forks and headset would be used to steer.

The resulting cycle would be small. A puny-farthing.

 

 

 

 

 

 

 

 

The front axle would need to transmit the power from the pedals and so a new hub was machined. This was a simple stepped axle to locate the bearings and pedals, but it also had to have some way of attaching the spokes.

The solution was to make 2 discs from a slice of 50mm bar. These were bored 20mm to fit the axle and drilled to take the spokes.

Disc being bored to fit the axel.

 

 

 

 

 

 

 

 

The spoke holes marked out

Marking out the 18 spoke holes was done by using the computer to plot a circle with lines every 20. This was glued to a piece of board and attached to the rear of the headstock of the lathe. A height gauge was used as a pointer.

 

The results from this marking out were relatively accurate and good enough for locating the spokes which could always be adjusted to compensate when building the wheel. 

2 of these discs were made.

The holes were drilled and then counter-sunk to accommodate the curve at the root of the spokes.

 

 

 

 

 

 

 

 

A piece of 1" steel bar was cut to length and centre drilled in each end.

A reduced diameter section was machined on each end of the shaft to a diameter of 20mm, to locate in the hole in the centre of the discs. The shoulders were machined to leave a distance between the discs of 65mm.

 

 

 

 

 

 

 

 

The 2 discs were brazed onto the shaft up against the shoulders. The assembly was then mounted between centres on the lathe. In this setting some shoulders were machined for the bearings and pedals. The chosen bearings had an ID of 17mm and the pedals needed a shaft of 15mm to be held in place with cotters.

 

 

 

 

 

 

 

 

Method of checking bearing fit without removing shaft from lathe

 

Finished end detail with step for bearing and pedal.

Also in this setting the centre of the shaft was reduced in diameter using a profiling tool.

 

 

 

 

 

 

 

 

The milling machine was used to cut slots for the cotter pins,

Photo showing pedal and bearing fitted to one end of the shaft.

 

 

 

 

 

 

 

 

Once the axle was complete it was assembled into a rim and adjusted to run true.

The easiest way to re-spoke a wheel is to copy another one. If one isn't available then the best place to go is Shelden Brown's bicycle pages which are an unbeatable web source for all bike related stuff.

 

 

 

 

 

 

 

 

The front forks were modified to take the front wheel.

The wheel would need to be removable to enable a puncture to be fixed etc...

The front bearings were housed in aluminium blocks which were bored to be a push fit round the bearings.

 

 

 

 

 

 

 

 

The forks had the drop outs cut off and the end filed square. A piece of steel bar was cut to size and pinned in place on the end of the forks. Then it was brazed in place.

Finally the pins were ground off and the bearings checked for alignment.

 

 

 

 

 

 

 

 

The frame brazed.

The seat post was just cut and brazed to the frame.

The frame of the puny-farthing was a 1" piece of steel tube bent to suite using a vice and a piece of scaffold tubing to progressively get the required shape.

The headstock was also a piece of scaffold tubing bored to take some standard bearing cups. It was then brazed to the main frame tube and braced for extra strength.

 

 

 

 

 

 

 

 

Two old cottered pedals were fitted to the front axle. The pedal with the crown gear had the gear sawn off and the remaining area faced flat on the milling machine.

 

 

 

 

 

 

 

 

This photo shows the completed assembly before painting. A rear brake was fitted before a test ride.

The test ride confirmed two things.

  1. The bike was as awful to ride as expected.
  2. The pedal cranks were too long resulting in the rider's knees nearly touching the handlebars and too much foot movement for a given speed.

 

 

 

 

 

 

 

 

To fix the pedal crank length a 1.5" piece was removed from crank arm, near the pedal end where stresses were lowest.

It was important that the crank axis and pedal pivot were in-line so that the pedal would not rotate under the foot. So a piece of wood was used with two lengths of threaded rod to align the two holes. In this setting the two parts were welded back together

 

 

 

 

 

 

 

 

 

 

The finished bike

Truly useless and a dreadful ride !

 

 

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