I don't have a special tool for the job like Eric does, but I just use a small glass bottle. Here's the philosophy on it: the rod is bent because the wood is compressed on the inside of the curve and relaxed on the outside or hump. With arrows no heat is required, but with hickory I can see the benefit. So heat the wood in the area that needs straightening, lay the rod hump upward on a flat table, and rub the small glass bottle lengthwise along the rod to compress the wood. Several strokes, then have a look down the rod to see your progress. If it needs more, reheat and re-burnish. the rod will straighten out wonderously and stay that way. Of course, the same goes for your arrows. Don't store your arrows in their quiver...that's asking for warping.