![]() While I’m talking about bolt locking techniques, I’ll share another interesting one: For double nut connections involving the use of a jam nut & a standard nut, it REALLY matters what order you install them in. Double Nutted joints with jam nuts are affected by order of clamping. *F) Alternate Testing Video #2 making the counter argument in favor of split washers. *E) Alternate Testing Video #1 making the counter argument in favor of split washers. Since this one is sure to stir things up when you mention it the guys at the office, I‘ve provided my sources below.Ī) Article 1 n and Article 2 on and Article 3 on, all condeming split washersī) pdf file from condeming split washersĭ) Awesome video showing actual testing and how preload decay charts are generated. No amount of vibration will break this kind of connection: When lives are on the line you may want to employ a ‘positive locking device’ such as a castle nut or a slotted nut. Serrated flange nuts are probably the best way to go. If you have some money to burn then wedge lock (Nord-lock) washers & ![]() Not to worry, there are better locking options available. Chemical lockers like Loctite, deformed thread lock nuts, and Nyloc nuts should be your everyday go-to locking devices. When he compared the preload decay of a bolt & split washer combo to bolt by its lonesome, he found that the split washer caused the connection to loosen sooner, as seen below.* His second discovery was made by plotting the bolt tension vs vibration cycles to create a ‘preload decay chart’. The first thing he discovered was that transverse vibration loads generate a much greater loosening effect than do axial vibrations. He invented a machine specifically for testing the effect of vibrations on threaded fasteners. The evidence against split washers started stacking up in the 1960’s when a gentleman named Gerhard Junker published some of his lab experiments. The only time a split washer might prove useful would be for fastening onto soft easily deformed surfaces such as wood, where the washers springiness & sharp edges could actually work. The problem is that split washers make for poor springs and bottom out after only a small percentage (on order of 10%) of a bolt’s total clamping load. In practice a split washer is unable to gain any purchase against hard surfaces and does not actually prevent rotation. ![]() ![]() At this point the sharp edges of the washer are supposed to dig into the nut and mounting surface to prevent counter-clockwise rotation. In theory split washers (aka lock washers or helical spring washers) are supposed to work by squishing flat between the nut and the mounting surface when you tighten them. ![]() And yet I see these things in use everywhere, so what gives? Split washers have been experimentally proven to be ineffective locking devices and can even aid self loosening over time. When faced with contradictory test results, if we assume the methodology and integrity of all sources are without fault, it is reasonable to conclude that your results may vary. Many factors could significantly affect testing results including variances from manufacturing process, fastener & clamped materials, heat treating, surface finishes, ambient conditions, and bolt diameter.ġ. In the interest of transparency and good scientific discussion, I’ve provided links to all sources mentioned at the end of point #1. UPDATED MARCH 2017: It has come to my attention that there is testing data available that makes the counter argument to my first point in this article. What follows are 10 tricks on this ‘basic’ subject that might surprise you! You’d expect an engineer to know everything about a basic subject like nuts and bolts right? Well fasteners are one of those topics that seem simple at first but turn out to have much more depth than you expected. ![]()
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