Pietenpol-List: Turnbuckles and Common Sense
Posted: Mon Feb 18, 2002 11:37 am
Original Posted By: Kent Hallsten
I hate to get involved in this discussion, but I got some advice from afarmer-turned-engineer about 25 years ago that seems to bear on thissubject.Think real hard about what an AN turnbuckle and a home depot turnbucklelooks like. Forget about the materials for now. The ends of the ANturnbuckle are a continuous loop, while both hook and eye end of thehardware store devices are bent wire. Now imagine taking a big pair of slipjoint pliers and unbending the loops. If you can't imagine doing that, youprobably know someone who could. Now think about the ends of the ANhardware, and doing the same thing. I can imagine bending it a bit, andscratching it up, but not opening it. Get out your imaginary welding torchand at least weld the loops closed.Now think about the barrel parts of both turnbuckles. I don't know what thehardware store varity is made of. I'll assume they're forged, sort of likea very light, inexpensive C-clamp, but there's no material specification--itcould be die-cast zinc. Think about the shoulder of the turnbuckle where itbends from the threaded part to the straight part. If there's a problem itwill be at the bend. Remember how the light C-clamp twists when it'sovertightened? Quite honestly, I don't really see the barrel coming apartthat way, but I can certainly imagine a flaw in the casting that lets oneside part. You know what a broken casting looks like: a rough slantedsurface with a view of the crystal structure. If you're even going to thinkabout using one of these, clamp a test piece in your vice, take a slegehammer, and see how it breaks.There are about 30 turnbuckles in the entire airplane. Total cost is lessthan $500, without the 15% AS&S discount. I would love to save the moneyusing hardware store devices on my plane. But for me, it's the hardwarestore stuff that doesn't get past the common sense test.Gene Hubbard ________________________________________________________________________________
I hate to get involved in this discussion, but I got some advice from afarmer-turned-engineer about 25 years ago that seems to bear on thissubject.Think real hard about what an AN turnbuckle and a home depot turnbucklelooks like. Forget about the materials for now. The ends of the ANturnbuckle are a continuous loop, while both hook and eye end of thehardware store devices are bent wire. Now imagine taking a big pair of slipjoint pliers and unbending the loops. If you can't imagine doing that, youprobably know someone who could. Now think about the ends of the ANhardware, and doing the same thing. I can imagine bending it a bit, andscratching it up, but not opening it. Get out your imaginary welding torchand at least weld the loops closed.Now think about the barrel parts of both turnbuckles. I don't know what thehardware store varity is made of. I'll assume they're forged, sort of likea very light, inexpensive C-clamp, but there's no material specification--itcould be die-cast zinc. Think about the shoulder of the turnbuckle where itbends from the threaded part to the straight part. If there's a problem itwill be at the bend. Remember how the light C-clamp twists when it'sovertightened? Quite honestly, I don't really see the barrel coming apartthat way, but I can certainly imagine a flaw in the casting that lets oneside part. You know what a broken casting looks like: a rough slantedsurface with a view of the crystal structure. If you're even going to thinkabout using one of these, clamp a test piece in your vice, take a slegehammer, and see how it breaks.There are about 30 turnbuckles in the entire airplane. Total cost is lessthan $500, without the 15% AS&S discount. I would love to save the moneyusing hardware store devices on my plane. But for me, it's the hardwarestore stuff that doesn't get past the common sense test.Gene Hubbard ________________________________________________________________________________