Steel Yourself

"Phew, something that's not fibreglass", sighed George.

Materials

Almost all of the chassis is 25.4mm square or round 1.6mm ERW tube. Major cross members are 50mm 2.5mm box section while the VW beam mounts are 40mm 3.0mm box section. Structural panels are 1.6mm sheet steel. Steel cost was about NZ$800.

Construction

The actual chassis build started in August 07 and, after about 200 hours work, was finished in Aug 08.

The build was in three modules: (1) Front VW beam mount plate; (2) tub; and (3) rear suspension box. These were propped on a centreline and joined. All measures and squares were taken from one point – the rear firewall - always, always measuring diagonals.

The Stanley Fat Max level became a new friend. "Stainless steel" 1.6mm cut-off discs and hacksaw made short work of the ERW tube. At NZ$4 apiece the discs also made short work of the budget. One 100mm NZ$35 angle grinder died for the cause.

Of course there were about 500 awkward cuts. Double ‘fish mouths’ were avoided (fussy fabricators look away now) by not taking tubes fully into corners, using square tube for the tricky bits, and partially flattening some round tubes. Nevertheless some of the angles were so incomprehensible that they first required dummy parts made out of wood with a filler end that would mold to the required shape. Sadly elves did not magically turn these into steel.

It was tacked using a cheapo gasless MIG. Ready to spring apart at any second, it was trailered to a local race car engineer who did the full welding, see the update page. While he complained about the galvanised RHS, he took the crappy tacks in his stride and provided the expertise and encouragement that the project needed.

As built

The front is now sheeted rather than diagonally braced. This also gives a strong passenger cell that, in a prang, should resist penetration from suspension parts and be well isolated from the front mounted fuel tank. The firewall provides the bracing above the knees that was missing in the CAD. The complex mount at the front carries the VW beam while the spidery nose piece carries the radiator and body - and is crushable in a frontal impact.

Tubes are coming and going... Those above the engine also tie to the safety belt mounts and are removable. Tubes are ‘doubled’ around the bell housing. The holes in the cross members knock 1.5kg out of the 2.5mm box section. Wishbone bushes fit neatly inside the cross members.

The seatbelt mounts were positioned using a cardboard H point template placed on the seat (in the LVVTA regs). Then followed fiddly juggling of seat runners, 3mm reinforcing plates, anti-crush bushes and extra chassis tubes.

Sadly the Club's technical experts felt the mounts were not quite right. For a four point harness they should be closer together at the shoulder, while the lower mounts should be further forward so that the lap belt sits over the hips (rather than the driver's ample tummy) - to prevent the driver and passenger from submarining under the dashboard in a crash.

By the time it all comes together it is apparent that it is a system, not just a chassis. For example, so much depends on where the seat goes: seat runners -> gearshift cable run -> engine mount. And a cock-up can set plans back by a month. For example, engine too far back and can’t separate the tranny -> move engine mounts -> starter fouls the frame -> swear and throw toys.

But as evidence you can think it out beforehand, the actual build weight was 101kg or within 3% of the CAD estimate.

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