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broox: Here's what it looks like when closed
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broox: Folded open
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broox: So, let's say you want a dado centered along this line
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broox: Simply line the shorter straight edge up with the center of your desired dado and clamp the jig down
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broox: Fold the hinge over and run your router along the straight edge
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broox: Because the folded over piece is exactly half the width of your router base, your router will be perfectly centered.
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broox: Routing that dado
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broox: And that's it