Ariel, it has nothing to do with right or left. It refers to the cutting direction of the bit itself. For instance, in cutting a mortice in solid wood you would probably want an upcut because it cuts in an upward spiral and draws the chips upward out of the hole. On the other hand, if cutting a dado in plywood you might want a downcut because the downward spiral of the bit will be less likely to splinter the plywood layers. There are other uses, but these are just examples. Hope this helps.
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City where the west begins.