Up or Down Spiral Router Bits?
Quality solid carbide spiral bits combine effective chip removal with a continuous shearing action cut not obtained from a standard straight bit. Carbide bits offer smoother cutting action with better results.
Up-cut Bits provide faster cutting while they pull chips up and out of the work or towards the router. They are excellent bits to use when cutting material in a router table since they tend to hold the work piece to the table itself. Ideal for mortise and tenons, grooving, slotting or routing deep blind holes. Down-cut Bits cut slower and push chips away from the router to eliminate top surface splintering. Use for pattern cutting or when going completely through the board as it allows clear vision of the cutting line. Ideal for fine finish work such as veneers, laminates, inlays and repairs because they prevent upper edge tear outs. Use Down-cuts for trimming and sizing.
Compression Bits Cuts through stock and gives clean cuts in both top and bottom. No tear out as bit is designed to pull work into the center of the stock. Ideal for double sided veneer plywood, melamine, and laminates. As for size recommendations, it really depends on the specific application you intend to use the bit for. We find that the 1/8″, 1/4″ and 1/2″ Up-cut and the 1/4″ and 1/2″ Compression bits are the most popular for wood applications.