Thursday, December 8, 2016

Front End 1 : Go Aluminum

Tubular Steel
So the front axle of the Stevenson formula calls for a tubular steel "drop axle". This usually is fabricated using a tube bender and a welding fixture, or cut and weld angles of tubing. Sometimes builders use square tubing to avoid having to fab mounting brackets, square tubing weighs a bit more so there is a penalty- but it saves time and is more accurate to have a flat surface to mount things to like leaf springs and trailer bolts. If you do some research you may find that vintage Ford designs of drop axles have various sections, designs, and weights depending on the purpose.

This requires a fixture, a welder, and a margin of error. The point is to establish jounce clearance above the axle for the chassis, and to allow a half-round leaf spring (or springs) to cushion the ride vertically. The pros-and-cons of doing this are debatable, suffice to say that this technique works well enough for most cyclekart builders.

Leaf springs are relatively challenging to find in small sizes. But this is one of the fun elements of this hobby - finding your own answer to the problems at hand. If you have the ability to have a local shop oil quench some mild steel, it's easy enough to make your own half-round springs for a nominal price. I leave it to you to find out more. One clue I can offer is that horse-drawn buggy supply companies offer a menu of springs of all sizes...and purposes.

And finally there are modern version of half-round leaf springs that are made from carbon fiber.

Air Trekkers CZ Carbon-Fiber Leaf Springs

Below is the concept for the Type 69 axle, an all aluminum tube axle with kingpin joints derived from a square tube section of aluminum. It is strong, flexible, and will be easy to adjust. In hindsight, it could have been a square section which would have been easier to make square to the brackets. At the end though the round shape gives me the flexibility to change the caster angle at any time - an ongoing topic with cycle kartery.

The spacer in the middle keeps the axle from shifting, I am using trailer bolts to lock the front leaf springs to the axle. The trailer bolts are easy to find at any hardware store.

The measurement for the axle was off the first time I cut it, because I forgot to factor in the length of the spindles. So i had to cut down the length to count for the very long Azusa spindles. To keep the front axle from shifting left-to-right, or twisting, there are two 'set screws' that lock the axle to this spacer collar, which frictions against the 'washer plate' on the top.

Choosing aluminum here saved me alot of weight. The steel axle as specified weighed 10 lbs without any hardware. It was strong, but not light. The aluminum version here weighs 4 lbs without hardware, but includes the kingpins and has a measure of flex.


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