Brodhead Pietenpol Association

Original Posted By: owner-pietenpol-list-server(at)matronics.com
Hi DJ,You need a little more information - specifically, how many threads will youhave engaged? Threaded holes typically fail by shearing across the threadroots, so you will need to calculate the area of the thread roots,multiplied by the number of threads engaged, multiplied by a healthy safetyfactor. 7075 is not too bad for fatigue (for aluminum), but with cutthreads you will have some significant stress risers. Personally, I wouldtry to have a factor of safety of at least 5. If the Lift struts let go,you will have a very bad day.Given a choice between aluminum and steel for such a part, I would go withsteel due to its increased fatigue resistance, unless you have a largesafety margin. What about corrosion? What will this block be attached to?Steel or aluminum lift struts? If steel struts, then definitely make thisblock of steel to avoid dis-similar metals setting up galvanic corrosion.If aluminum then I would lean towards an aluminum block, preferably with abarrier of oil on the steel threads of the strut fork to avoid corrosion.Jack Phillips -----Original Message-----

Original Posted By: "DJ Vegh"
DJ,Jack is correct in saying that it's based on the thread failure. However,and this may not answer you question directly, the height of a basic nut hasbeen determined so that failure based on the area of threads is greater thanthe failure based on the cross-section of the bolt. This is not a absoulteengineering solution, but it helps one visualize the strength of the threadscompaired to the strenght of the body of the bolt.To determine failure, you have to figure the problem three ways: 1) willthe threads shear off of the threaded rod, 2) will the threads shear off ofthe threaded hole, or 3) will the rod fail in tension at it's smallestdiameter (which is likely the minor diameter of the rod's threads). Trylooking at pages 1490 from the Machinery's Handbook (I have edition 26)which has all the formulas for this and specifically has formulas for whenthe material of the threaded hole is weaker than the threaded rod.Robert HainesDu Quoin, Illinois

Original Posted By: Michael D Cuy