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Model A chassis, introduction:
In this series we will follow
the construction of a Model A chassis. This isn't intended to be the
definitive how-to, as there are multiple correct ways to perform any
of the individual steps in this process, and we will not assume that
our way is the only way. In this introduction, we will prepare the
chassis for boxing.
One advantage we do have is a jig to which we can clamp the rails, which minimises the distortion that is inevitably created when so much welding is performed. This isn't a production jig, but it is square and dimensionally accurate to less than half a millimetre. The rails are RodTech reproductions, pressed out of 4 mm plate; the attendant boxing plates are also 4 mm, 25% heavier and stronger than original Model A rails.
Given that a stock, 76 year old Model A chassis, with stress cracks and serious rust, fetches about the same price as a the RodTech components, and that the guidelines allow the use of repro rails, that decision is a no-brainer. Some states have different rules relating to repro chassis - if you are planning a new chassis, check first.
These rails were purchased 5 years ago, and as a result of sitting in a damp shed, are covered in a light film of surface rust, which requires mechanical removal, with a wire brush and sanding discs. New rails are shiny steel, so that step is normally not necessary.
Model A Fords have a simple chassis, consisting of steel channel, or C-section longitudinal rails, and formed channel cross members that are riveted to the rails. The chassis were designed to flex a lot, as the suspension was quite rigid. Our setup is going to have a RodTech independent front suspension (IFS) and a Jag rear, both supple examples of modern suspension, so a more rigid chassis is required.
The V8 engine has heaps more torque than the original 4 banger; another reason to box the rails. Boxing refers to converting the rails from C-section to a box section, by welding on a 4th side, the full length of the rails.
The jig was a fortunate find; not everyone will have access to such a handy item. This one will have at least 3 chassis on it in the next 6 months, so if you and some friends are considering new chassis, it might be worth your while to build your own. You might also put rotisserie style pivots at the ends too - the possibilities are endless.
Before we began boxing, we examined the rails for over-stamping, a situation that happens in production, where the extremities of a fold are bent at more than 90º. We pounded the rails with a 4 lb hammer until the folds were 90º - a straight edge confirmed how straight the top and bottoms were. See illustration 1.
Root nuts have been around for decades, but some rodders prefer to weld in chunks of steel and drill and tap the holes after the boxing is in place. Either will work, but we find Root nuts a cleaner and simpler solution. If the rails had been made from RHS we would not have been able to use Root nuts, but then we wouldn't have such a large weld along each join either.
After the boxing plate had been tack welded to the rails, the rails fitted the jig without any force required to bend the rails to conform to the shape of the jig. That is important, as our next step is to remove the rails and weld them full length, outside the jig.◄
Accreditation: The Editor.