I work with cast springs often, about 90% percent of my work is done with casted springs from 6150 steel. The quality of the lost wax casting and the foundry’s pour are what make the difference in a cast springs quality. Positioning the spring is critical on locks for maximum energy, if a spring is placed too far or too low by a few MM, can be the difference between a great sparking lock and a mediocre sparking lock. When initially getting started on a lock the first i look over is the spring for kinks, cracks, voids and extra waxed over areas that indicate a correction by the caster (if the original was bent or broken).
CNC machined springs i have found to be heavy at times (not talking about Kibler springs here) because the machining processes used for often doesn’t capture complex designs or at least the techniques used by the designer didn’t consider it, the cutting process used for springs may also be flawed. Machined springs that are sold as ‘tempered’ and ready to drop in often are too hard. Machinist and metallurgist have suggested to me the machining processes used could be work hardening the product from overheating, poor cutters and or the burning of cutting fluid can sometimes carburize areas or of course improper programming can lead to a poor design. Over the years I’ve seen some great ones and some really rough looking ones that were nearly impossible to lighten without removing 30% of the lower leg, these made better use as paper weights than lock springs. Can a CNC spring be superior to cast, of course, it depends on the facts and circumstances of everything else and on any given day a cast spring could be superior to a CNC spring.
The original lock makers designed their springs after long periods of tedious failures and successes in forging springs, imagine how many must have been tossed aside. With casted springs, i do feel we are copying their best designs if the caster has chosen wisely. CNC springs that utilize programming often attempt to correct perceived flaws because well, we often imagine ourselves to be smarter than our predecessors i suppose, so its done.
Forged springs if done carefully and correctly are superior to both Cast and CNC springs, I’m not a metallurgist here just stating what iv’e noticed on my bench. Forged springs crafting techniques are extremely important, getting appropriate shapes and bends are critical or the entire part can be easily ruined with a wonky bend. One of the best springs i have in my shoppe is an original long land mainspring, complete with its elbow bending mark in all, the design of it, the tapering and width of the parts produced a spring that still works from its original temper 270 - 300 years ago with lower quality spring steel. Forged springs made in a die in my opinion are of the best, a lot reasons why, i believe its because of high load compression, temperature resistance during the forging process, and precision in the shaping of the legs, with a slightly oversized die made spring, one can file it in lesser critical areas to lighten it, i was able to accomplish this with a smith who was making rifle locks springs and musket sized springs from a die. A great example of die made springs were by Miroku, these were often very heavy left in a raw unshaped state, important to note that miroku made forged springs and casted ones too, they chose the method best suited for the project.
At the end of the day if the builder knows their craft, they’ll make a high quality product. But if i had my choice and the resources I’d have my springs forged in a die.
