Self-centering doweling jig - how does centering work?

The threads reverse at the center section. There is a smooth section in the middle of the threaded rods that ride in a bearing in the center part of the jig, so the center piece never moves on the threaded rods. Since the threads to either side of the center section are revered from each other, both side either move in towards the center or out, as the threads rotate, if that makes sense.

Like Rumpy said - that's the theory. I have one and it never seems to line up perfectly - that's the reality. I don't think that the thread rotation is perfectly in synch. (front

- rear).

Not a bad jig to have around when you need it tho.

Lou

There's another kind of centering jig, too. The kind I'm familiar with doesn't use threaded rods at all, but has two pins, with the drill guide hole perfectly centered between them. So long as the two pins touch opposite faces of the stock, the drill will be centered. No moving parts, no adjustments.

Kevin