BLEVEN’S TECH TIPS

Tech Tips May 2004

Nuts About Bolts? Or About Nuts and Bolts

Everyone knows all about bolts, right? Bolts come in many sizes and many lengths. They have different grip lengths, different hardnesses, and different shear strengths. Theycome in nylon, bronze, nickel-copper, stainless steel, brass, aluminum, titanium, silicon bronze, nickel-copper, fiberglass, Teflon, ceramic, pvc, and even in wood. Some bolts are drilled, some have cut threads, and some rolled threads. There are different bolt heads, different thread lengths, and different threads per inch counts. There are carriage bolts, stove bolts, allen head bolts, recessed bolts, toggle bolts and spring bolts, tapered bolts and split bolts. Bolts even come with nylon stop pins set into their threads, or, with self-sealing heads. Bolts are designed for specific jobs. Proper selection of bolts for an airplane is of course critical. Those who have this understanding will consider the job of each bolt subconsciously. Improper use or application invites failure down the road. A bolt that is too hard may snap like a piece of glass. One that is too soft can stretch and become loose. If the bolt’s grip length is too short, the threads will probably wear into the part the bolt is securing. If the threads are not completely through the nut, the nut will not have the same strength that the bolt has. I recently discovered that if I used a stainless steel nylon lock nut on a stainless steel bolt, about one in five would broach the threads. Go figure. I am still learning.

Bolts can be used in both a shearing load and at the same time, in a tension load. When this is done, each of the resulting loads will compromise the rating of the other. As an example, if the bolt in question is used to solidly support two brackets, as in a bushing between, with a rotating pulley, or with a bell crank on the bushing, the shearing strength of the pulley load would be reduced because of the tension load on the bolt. For the most part, this type of application will have more benefits than otherwise. We should have a good understanding of the loads placed upon these bolts and use the right bolt and nut for the job. Also, we must tension it properly for the application.

Did I forget to mention that rivets also carry the same ratings, those being for head dimensions, diameters, lengths, and hardness? And again, shear and tension must be equal to the intended loads. Oftentimes, a bolt or rivet is used as both a fastener and a means of enhancing the strength of the bracket it is attached to. This is another reason for not straying from aircraft quality parts and fasteners, for to do so could shorten the life of more than just the aircraft.

The proper fit of the bolt to the hole is every bit as important as is its strength. And also, let us not forget the importance of the nuts we use. They too come in quite a variety. There are fiber stop nuts, nylon stop nuts, metal lock nuts, castle head nuts, shackle nuts, clip nuts, and nutserts, as well as some I probably have forgotten.

You might note from reading these tech tips, that the subject matter I select stems from various parts of my life experiences, sometimes from things I’ve read, sometimes from what people have told me. Til next time….

Dick i.d.k.s. about this either NEXT TIME WHEEL ALIGNMENT!!!!!