Quote:
Originally Posted by benz
Hi Allen,
Pretty nifty--I wouldn't have thought of covering a piece of rod. I was going to have a little spliced loop that would accommodate the toggle every place that it was necessary. I don't have sails with headboards, but that's a nice way of getting the pull straight. I had considered drilling a small hole in the middle of a metal (bronze, of course) pin, spicing the line over the hole, and then carefully working a cotter pin through both legs of the loop and the hole, thus keeping the pin from slipping out of the splice. It could also be lockstitched that way...
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I thought about a hole in the rod but it would be right where the stress was the highest and I didn't want to compromise the strength. I should have thought about it more as I just ran some numbers for this reply and it isn't that bad, especially if aligned correctly.
I noticed the toggles that SOAK are going to offer are 10mm in diameter and neck down to 7mm. My rod was about 8mm. The dogbone is then about 45% heavier and roughly 60% of the strength of the solid rod. On the other hand, drilling a 1/16 inch hole in a 5/16 rod would decrease its strength only about 3% if aligned perpendicular to the line and would be 68% stronger than the dogbone. It does seem to be very sensitive to the alignment of the hole as aligning it parallel to the line decreases the strength by 34%. In any event, keeping the hole or holes more or less perpendicular is how you would want it and it would still be stronger than a dogbone that necks down to 7mm.
I ran these numbers quickly so I hope I didn't get them wrong. The main point is that most of the strength of a beam comes from the top and bottom surfaces (think I-beam) so that a hole that runs perpendicular to the load doesn't change the strength much. On the other hand, the strength is diameter to the 4th power so a very small increase in diameter makes for a much stronger toggle.
One more point of interest. If aluminum is 2.7 times heavier than oak and 20 times stronger we can increase the diameter of the oak by 2.1x and get the same strength toggle and be only 16% heavier. Not bad.