Sweeps were used from the beginning of automobiles, although there was no standard for them in the early days. Initially they were just sawed out of mahogany as either true radii or as very large “French curves.” A French curve has a constantly changing radii (this could be a predictable change like one unit up, two units over, two units up four units over, three units up nine units over, etc. or something else).
In 1927 Harley Earl, who was working for Don Lee in CA designing car bodies for the new wealth in Hollywood, was offered a job to set up the first design studio in Detroit for GM. The first car entirely designed in a studio was the 1927 LaSalle, which had cues from European cars (Hispano-Suiza specifically).
As a kid Harley had vacationed in an area near a river where the bank had a damp clay that could be molded, so he started molding cars out of it, along side the bank. Zipping forward to Harley at GM . . . he decided to use clay to show the actual car, and then a way of "quantifying" the curves.
He drew on the system that was used for railroad track layouts (a similar system is used in auto road development), and came up with a numbered set of true radii from 1 to 100 that indicated the number of 1/8" rises over a 60" cord in a true arc or "sweep". It stuck and became the standard.
a) Sweeps: It varies in numbers of pieces depending on the set, up to 85 pieces. The radii go from 7200" to 42". These are now available in anodized aluminum or aluminum-clad plastic.
Aluminum clad plastic: 4mm thick, parallel (same sweep number on inside and outside of sweep): Full set is 85 pieces. Made in the USA, Milled surfaces for higher accuracy in viewing contours. Now in stock and available for immediate delivery. $3,000 for full set; $2,000 for half set (every other number).
Aluminum: Call for price.
b) Radius gauges: Developed by Fay to nest right in the middle with a dozen radii from 36" to .750".
c) Standard machinists radii sets that go from 1/2" down to 1/64". These can be purchased from any machinists supplier.
With these three sets, you have every radius you’ll ever need, and a standard in quantifying radii which parallels the manufacturers. For street-rodders drastically cutting cars or complete new redesigns, these systems are a must.
Buy one or a complete set. Call to order (413) 477-6449.
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