Thomsen Motorsport: Project FVT05 Part 3

Part 3 – Chassis and Transmission Upper Sub-Frame

Construction of the chassis gets underway consisting of over 100 sections of round steel tubing. This part of construction is the most intricate and time-consuming step in the project as each part needs to be cut and welded precisely to from the frame and ultimately, forming the skeleton of the vehicle.

The chassis construction must follow comprehensive Formula Vee rules and guidelines. Specifications such as materials, dimensions, safety considerations, envelope for the driver and attachment of components are all outlined in the rules and must be adhered to.

Following the commencement of the chassis, the upper transmission sub-frame is started. This section supports the engine, gearbox and suspension; which is mounted at the back of the vehicle. The frame is measured and cut accurately as per the dimensions in the SOLIDWORKS drawings. This is completed with some solid welds to ensure the piece is firm, sturdy and will have a decent track life.

SOLIDWORKS was used to create 2D templates for each piece of unique tubing required to form the frame. The templates were printed on sticky paper and placed at the end of tubes to show precisely where cuts should be made. A tube notcher and a bench press with a metal-cutting hole-saw were used to properly cut the ends of each tube.

For tubes that require an edge with a more acute angle; a hand grinder, bench grinder and deburring tool were used to achieve a closer, cleaner edge. This accuracy was again achieved by following the templates created with SOLIDWORKS that were stuck on the end of each tube. Each piece must be welded together in careful order so that every piece fits together to ensure a strong structure for the vehicle. Failure to do so would result in difficult or unstable welds, which definitely needs to be avoided if the chassis is to exactly match the dimensions and measurements as they are on SOLIDWORKS.

The roll hoop is the first section to be bent and pieced together. An external supplier was contracted to create the exact curve of the roll hoop in accordance with the Formula Vee rules and original design in SOLIDWORKS to within 1-2mm. From here, members are tacked to the roll hoop so that a base can be established. Side members are assembled separately instead of adding them piece by piece so that work can be done with more attention to welds and less attention to measurements and angles.

Before assembly could begin, there was a need for a stable and dimensionally accurate base to work from. SOLIDWORKS was used to design a chassis jig, perfectly suited to the dimensions of the frame. It acts like a rotisserie with pivots on each side to suspend the chassis at an accessible angle to enable access to the welding points from a variety of heights and angles. The welding quality is optimised due to the increased comfort of the welder and unobstructed access to the welding points.

With the newly created chassis jig, the roll hoop is suspended at an angle ready for the various steel tubes (members) to be attached. Support and front-lower members are welded first which will make up the frame for the full length of the chassis. From here, the car is built upwards and forwards starting with the front-middle rails. The main four longitudinal rails are attached as well as the support and bracing beams. Once each member is interconnected, the front end of the chassis is complete.

The next post will cover the bodywork plug which involves bogging, sanding, painting and moulding the surface of the plug. This will then form the outer fibreglass shell of the car which will later be attached to the chassis.

For Part 1 & 2 of Project FVT05, click here.