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Slot Car Body Technical History


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#1 Steve Okeefe

Steve Okeefe

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Posted 06 March 2013 - 08:39 AM

A Short Technical History of

Slot Car Bodies

By Steve Okeefe


 

It seems a contradiction that the body of a slot car, vintage or modern, is among the most ephemeral of components, an expendable item not unlike tires and braid, and yet is the single most important identifying part. If it is true that the clothes make the person, then it is likewise true that the body makes the slot car. Even in the "old days" we didn't speak of the "car with the blue motor", or the "car with chrome plated chassis", so much as referring to it as the "Yellow Lola". Indeed, when speaking of "Ready-to-Run" cars it is very difficult to separate the product as a whole from the body as a part.


Although modern slot car bodies are mere wisps of exotic plastic and paint, and most are a standardized actual size, hardly scale or even recognizable as the prototype they represent, this was not always so. Up through 1966, almost all slot car bodies were accurate scale representations, if not scale models, and through 1965 chassis were built and motors were selected to fit the individual body. This is an important distinction, for during and after 1966, rules increasingly allowed variances from scale (beginning with body width and tire sizes) to accommodate the realities of slot car physics, which unfortunately is utterly indifferent to the disciplines of scale modeling.


Slot car bodies, especially scale bodies, are notoriously difficult to fabricate from scratch at a workbench. In the early 1960s a few brave and skilled scratch builders (Jose Rodriguez among them) would carve and hollow out blocks of soft wood (commonly balsa) into scale size shapes that represented the prototype they were modeling, and then paint and race them!  Most racers on the other hand simply adapted the cheap and plentiful supply of injection molded hard plastic static model bodies.


By the end of 1962, some entrepreneurial types such as Bob Braverman were producing handmade fiberglass copies of their carvings, and the "body business" came into being. Now builders had a choice (albeit small) of bodies purpose-built for slot racing. Looking for an easier way, another bright individual decided to try vacuum-forming heated plastic (typically thick, opaque styrene) over (or into) a custom mold made especially for the purpose.


This worked surprisingly well, but all the bodies up to that point were not much lighter than the injection molded hard plastic static model bodies they replaced, and because they were opaque, still had to be painted on the outside, leaving this meticulous work exposed to the rigors of competitive racing. The only real advantage "purpose-built" slot car bodies had, especially the open top sports cars with driver positions close to the rear axle, was that the interior could be shaped to fit the relatively large motors underneath, usually by making it flush, or nearly flush, with the body itself.


Searching for something thinner (e.g.: lighter) to vacuum-form slot car bodies from, manufacturers discovered newer and tougher classes of plastics, including "Butyrate". Butyrate was tough enough to make a sturdy body only 1/32" (.032") thick! The fact that plastics like Butyrate are commonly transparent is probably a happy coincidence, for now slot car bodies could be painted on the inside, so paint jobs generally lasted the life of the body. Even so, some manufacturers such as Hawk didn't catch on to the transparency thing right away, and made their bodies out of tinted plastic.


A few manufacturers tried forming their clear plastic bodies by pressure-forming (a.k.a. blow molding), as opposed to vacuum-forming, in a manner similar to the way plastic bottles are made. With blow-molding the fine details (body lines, grilles, scoops, gas caps, etc.) are molded into the outside of the body (where they belong) and stand out much better.  Unfortunately, negative molds are considerably more difficult and expensive to make than positive molds, so the blow-molding process didn't work out so well economically for making slot car bodies.


The technological trend was toward lighter, wider and lower bodies, and this was not missed by the manufacturers. It wasn't too long before bodies were being vacuum-formed out of .020", and then .015" thick clear Butyrate. They weren't nearly as sturdy as bodies made of .032" , but their lighter weight contributed significantly to the car's overall performance, and they were cheap, plentiful and easy to replace when inevitably damaged during racing.


Meanwhile, a new and almost incredibly tough plastic called Polycarbonate, trade name Lexan, which had been developed by General Electric in 1953 and patented in 1955, was becoming more available for industrial and private use. Lexan bodies could be made of thinner material than Butyrate bodies, and would still be so sturdy and resilient as to be called nearly "bulletproof". For slot car bodies, Lexan was clearly superior to Butyrate.


In mid 1966, Model Products Corporation (MPC) produced a few vacuum-formed Lexan bodies, but unfortunately they used relatively thick material, which made the bodies far too heavy to be considered for competitive racing; they simply "missed the boat". Superior strength and toughness is not enough; the bodies must also be extremely lightweight. As it turns out, it wasn't until early 1969 that the major slot car body manufacturers such as Lancer and Dynamic "discovered" Lexan.


Continuing the trend toward lighter, lower and wider, serious competition slot car bodies are today made of Lexan only .007" thick, and are in addition just two-thirds as tall, fully 25% wider and weigh less than 1/4 of their mid-sixties .032" thick counterparts. In some cases they do actually resemble the prototype they are supposed to represent well enough to be recognizable, but a resemblance is all it can be called.


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