Hossack is not always as simple as it looks!

My first attempt at a Hossack front end was designed to be built as much as possible out of stock material - tube and box section - as possible. The ball joints were bought from a friendly neighbourhood motor factor for the princely sum of 600 baht (about €12).

The reasoning was that I wanted a reasonably skilled Thai fabricator to be able to build it without needing a well equipped machine shop.

The result was a little complicated to build. Quite a lot of jigging would be required.
The keen eyed amongst you will also notice that the bottom ball joint is in compression. After discussions with Arthur about reducing pre-load, it dawned on me that this type of ball joint was not designed to be loaded in compression. Shock loading it in compression could possibly pop the back out of the ball joint causing the ball joint to come apart.

After talking to my fabricator, I discovered that he was capable of fairly tricky sheet metal work. Here is an example of his work.

I set out to redesign the front end with the same dimensions, the bottom ball joint in tension and a fork fabricated from sheet metal. This is the result

As you can see the location of the ball joint centres is the same. This moves the mounts quite close together. Under braking, the inertia of the bike pushing of the ball joint will tend to twist the shaft of the ball joint, putting considerable force into the bridge of the fork.

This style of ball joint just doesn’t lend itself to this type of design. The risk is also that the stiction in the ball joints will adversely affect steering feel.

I had a meeting with my builder. Being a chopper artist he hated the look of the ball joints. He also pointed out the difficulty of fabricating both the tube fork and the sheet fork. He suggested I consider machining the front fork from solid billet. Once I had scraped myself off the floor and stopped choking, he explained that he had a friend with a CNC machine that could handle Solid Works models. He showed me a part his friend had machined for him for a chopper. It had cost under €20 but was being sold in the chopper catalogues in the US for about $300.

So back to the drawing board I went (there’s an expression that needs updating) and came up with the following rough sketch.