Quote:
Originally Posted by Ned Milburn
Single action truss rods need a curved channel. They operate by tightening or loosening to increase pressure against the curve.
Double action truss rods have 2 metal pieces that are solidly fastened at one end, and the other end can be adjusted to slip one metal piece against the other, to adjust the bow in either direction.
There are many modern style double action truss rods that are quite compact and lightweight that out-perform the single action style in so many ways. You can even buy these on e-bay for about 6 or 7 bucks a piece, or you can buy USA made for 30 bucks to 50 bucks or more...
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As I define it, single action only work against the string tension, whereas double action can exert their force either way. The single action rod i use, LMI's TRST, uses two full length pieces of steel, and has the same weight/bulk as most double action systems. I like it because I do not ever expect to need to combat a back bent neck due to my construction technique, and the adjust-ability is smoother, more accurate, and more stable than any double action rod I've tried. Basically, I find double action rods too finicky initially, and too often require attention down the line.